Vitamins & Supplements · Omega-3 oil
Fish oil
Marine omega-3 oil (EPA and DHA) · also called Omega-3 fish oil, EPA and DHA oil, aceite de pescado
Fish oil is a supplement that supplies the omega-3 fats EPA and DHA, which also come from oily fish. It reliably lowers blood triglycerides, but large reviews found little or no effect on deaths or overall heart events, and the evidence is weak or against for depression, ADHD and eye disease. Fish oil has been linked to more atrial fibrillation and may affect bleeding, so ask a doctor or pharmacist before using it.
General information, not medical advice. Last substantive update · Not medically reviewed. A named clinician has not signed off on this page. How this page is made
About Fish oil
Fish oil is a supplement that supplies the omega-3 fats EPA and DHA. It reliably lowers blood triglycerides. For heart attacks, depression, ADHD and eye disease the evidence is weak, mixed or against. The main cautions are atrial fibrillation, bleeding with blood thinners, and fish allergy.
What fish oil is
Fish oil is the oil from fish, sold as capsules and liquids. NCCIH says it supplies EPA and DHA, the two omega-3 fats most research is about. Fish liver oils such as cod liver oil are different: they also carry vitamins A and D. Krill oil, algal oil and flaxseed oil are other omega-3 supplements.
Products come in different chemical forms, mainly ethyl esters (common in concentrated products and prescription medicines) and triglycerides. A 2013 review says the form, whether you take it with food, and how the product is made all change how much EPA and DHA is absorbed, but it does not rank them.
Where the same fats come from in food
The NHS lists oily fish as herring (including kippers), pilchards, salmon, sardines, sprats, trout and mackerel, and says fresh and canned tuna do not count. It advises at least 2 portions of fish a week, one of them oily; a portion is about 140 g cooked. NCCIH says US guidelines recommend 8 ounces or more of seafood a week for adults.
Amounts of EPA and DHA per portion were not available for this page, because the USDA table could not be reached. They vary with the species, how it was farmed and whether it is canned. See the oily fish page for the food side.
What the research shows
The clearest result is that fish oil lowers triglycerides, by about 15% in a 2020 Cochrane review. For the heart, the same review found little or no effect on deaths, strokes or overall heart events, and a possible small drop in coronary events. A purified-EPA prescription drug lowered heart events in a drug-maker-funded trial, but a large prescription EPA plus DHA trial did not.
Evidence is very low for depression, against a benefit for ADHD symptoms and for slowing macular degeneration, and low for arthritis pain and memory. In pregnancy, a Cochrane review found fewer preterm births but more births after 42 weeks. Most of these results are for supplements; they do not show that people who already eat fish gain more.
Product quality
Three laboratory studies disagree. A 2015 New Zealand study found only 3 of 32 products had as much EPA and DHA as the label and most were oxidised. A 2016 Australian and New Zealand study of 10 products and a 2022 French study of 20 found products mostly met their labels and oxidation limits. The 2016 study says it aims to assist industry.
Food versus pills
Fish brings protein, vitamin D and other nutrients along with omega-3, and people who eat fish tend to have healthier lifestyles, so results for fish do not automatically carry over to capsules (NCCIH). Almost all trial results above are for capsules. This page gives no amounts to take; if you wonder about your own needs, ask a doctor, pharmacist or dietitian.
At a glance
Traditional uses history, not proof
- Eating oily fish for the heart
- Sold as capsules and liquids for heart, mood, joints and memory
Studied for research
- Source of EPA and DHA, high certainty
- Blood triglycerides, high certainty
- Heart events, mixed certainty
- Pregnancy and early birth, moderate certainty
- Arthritis pain and memory, low certainty
- Depression, very-low certainty
- ADHD, macular degeneration and cancer prevention, evidence against
Main compounds
- EPA (eicosapentaenoic acid)
- DHA (docosahexaenoic acid)
- Ethyl ester and triglyceride forms
Common forms
- Softgel capsules
- Liquid oils
- Prescription omega-3 medicines (different products)
Research links: 2020 Cochrane review: omega-3 and cardiovascular disease (86 trials) · 2019 VITAL trial: marine omega-3 and heart disease and cancer · 2021 review: omega-3 and atrial fibrillation · 2021 Cochrane review: omega-3 for depression · NCCIH: Omega-3 Supplements, What You Need To Know · Research Library · Genes & Biomarkers Library
What it is and its history
- Accepted scientific name
- Fish oil (marine omega-3 oil)
- Common names
- Fish oil (English); Omega-3 fish oil (English); EPA and DHA oil (English); Marine omega-3 (English); Aceite de pescado (Spanish); Aceite de pescado omega-3 (Spanish)
- Family or group
- Omega-3 fatty acid oil. NCCIH lists fish oil with fish liver oils (cod liver oil), krill oil, algal oils and flaxseed oil as the main omega-3 supplement types.
- Harvest and processing
- Not researched for this page. The prescription label says its omega-3 is obtained from the oil of several fish sources.
- Look-alikes and adulterants
- Name: Cod liver oil and other fish liver oils; Note: NCCIH says these also contain vitamins A and D in amounts that vary by product. They have their own page.; Name: Krill oil; Note: NCCIH says krill oil contains omega-3 in phospholipid form. It has its own page.; Name: Algal oil; Note: NCCIH says algal oils are a vegetarian source of DHA, and some also contain EPA. It has its own page.; Name: Flaxseed oil; Note: NCCIH says flaxseed oil contains ALA, the plant omega-3, not EPA or DHA.
- Sustainability and conservation
- Not assessed. The NHS notes that choosing a wide range of fish helps avoid overfishing, a point about eating fish, not about supplements.
What is inside, and how it may work
What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.
Main compounds
| Compound | Family | Where it is concentrated | Activity studied | Level of evidence |
|---|---|---|---|---|
| EPA (eicosapentaenoic acid) | long-chain omega-3 fatty acid | The prescription label states about 465 mg EPA and 375 mg DHA in each 1-gram capsule of its medicine; ordinary supplements vary and the label must be checked. | One of the two omega-3 fats most research is about (NCCIH). Purified EPA ethyl ester as a prescription drug lowered heart events in REDUCE-IT. 19 18 5 | Human data |
| DHA (docosahexaenoic acid) | long-chain omega-3 fatty acid | See EPA entry. | The other main omega-3 fat; the NHS and NCCIH link omega-3 intake to a baby's nervous system development. AREDS2 tested DHA plus EPA for AMD without benefit. 19 20 2 | Human data |
| Ethyl ester form | chemical form | Not read from a source. | A form used in concentrated products and prescription medicines. The label says EPA and DHA were absorbed from ethyl esters, with EPA rising in a dose-dependent way. 18 14 | Human data |
| Triglyceride, free fatty acid and phospholipid forms | chemical form | Not read from a source. | A 2013 review says the chemical form affects absorption but does not give a ranking. 14 | Human data |
Mechanisms, receptors and pathways
| Target or pathway | Gene or receptor | What was found | Level |
|---|---|---|---|
| Triglyceride lowering | Possible: DGAT enzyme, liver fat burning, lipoprotein lipase (per the prescription label) | The label says the mechanism is not completely understood, and lists possible actions: less fat made in the liver and more activity of the enzyme that clears blood fats. 18 | Human data |
| Absorption of EPA and DHA | Not applicable | The amount absorbed depends on chemical form, food eaten with it, and how the product is made. 14 | Human data |
| Nervous system and retina | Not applicable | The NHS says long-chain omega-3 helps a baby's nervous system develop. DHA is said to be concentrated in the retina, but no source read for this page confirms it. 20 | Human data |
Absorption, metabolism and elimination
- Absorption
- From the prescription label: EPA and DHA were absorbed from ethyl esters in healthy volunteers and people with high triglycerides; serum EPA rose in a dose-dependent way, DHA less so. A 2013 review adds that absorption depends on chemical form, taking it with food and fat, and product design.
- Distribution
- Not covered in the sources read. The label notes EPA and DHA appear in breast milk.
- Metabolism
- Not covered.
- Elimination
- Not covered.
- Bioavailability
- Varies with form and meal (2013 review); the review does not rank the forms.
Isolated compounds versus whole extracts
Fish oil is not the same as eating fish. NCCIH says that for some conditions the evidence for benefits from seafood is stronger than the evidence for omega-3 supplements, other nutrients in seafood may play a role, some benefits may come from eating seafood instead of less healthy foods, and people who eat seafood tend to have healthier lifestyles. Almost all trial results on this page are for capsules, not fish. See the oily fish page for the food side.
Nutritional composition
No per-portion amounts of EPA and DHA in fish are given on this page. The USDA FoodData Central table could not be queried (rate limit) and the NIH Office of Dietary Supplements page was blocked. What was read: NHS oily fish list and portion size (about 140 g cooked), and NCCIH on sources.
2 high certainty1 moderate certainty2 mixed findings2 low certainty1 very low certainty3 evidence against
What was looked at
The 11 benefits and uses checked for Fish oil, each with how strong the evidence is. Tap one to open it.
- A source of EPA and DHA (and how food compares)High certainty
- Lowering blood triglyceridesHigh certainty
- Heart attacks, strokes and other heart eventsMixed findings
- DepressionVery low certainty
- ADHD in children and teenagersEvidence against
- Pregnancy: early birth and baby developmentModerate certainty
- Joint pain in rheumatoid arthritisLow certainty
- Memory and dementiaLow certainty
- Age-related macular degeneration (AMD)Evidence against
- Dry eyeMixed findings
- Cancer preventionEvidence against
Lab markers tracked in the studies
Blood triglyceridesMajor cardiovascular events (heart attack, stroke, heart death)Depression rating scoresPreterm birth (before 37 weeks)
What is Fish oil good for?
The main studied uses and how strong the human evidence is for each. Most results are for capsules, in adults.
Benefits, one by one
Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.
A source of EPA and DHA (and how food compares)
High certaintyFish oil is a supplement made from the oil of fish. It supplies two long-chain omega-3 fats, EPA and DHA. The same fats come from seafood, especially oily fish such as salmon, mackerel, sardines and herring. NCCIH says that for some conditions the evidence for eating seafood is stronger than the evidence for supplements, and that other nutrients in fish, or eating fish instead of less healthy foods, may play a part.
2 studiesFish oil products: capsules and liquids, in ethyl-ester or triglyceri…
Studies, doses and limits
What the trials found
NCCIH says EPA and DHA are found in seafood, especially cold-water fish such as salmon, mackerel and tuna, and in fish oil supplements, while a different omega-3 (ALA) comes from plants such as flaxseed. The NHS lists oily fish as herring (including kippers), pilchards, salmon, sardines, sprats, trout and mackerel, and says fresh and canned tuna do not count as oily fish. The NHS says a healthy diet should include at least 2 portions of fish a week, one of them oily, and that a portion is about 140 g cooked. NCCIH adds that US dietary guidelines recommend 8 ounces or more of seafood a week for adults. Amounts of EPA and DHA per portion of each fish were not read for this page, because the USDA table could not be reached; they vary with species, farming and canning.
Results
Fish oil does supply EPA and DHA. Whether extra EPA and DHA from pills helps people who already eat enough is a separate question, answered use by use below.
Effect sizes as reported
No effect sizes apply; these are statements about what the oil contains and where else the fats come from.
Why this rating
High that fish oil supplies EPA and DHA and that oily fish is a food source (health-agency statements). This is not a claim that supplements improve health.
Form and dose studied
Fish oil products: capsules and liquids, in ethyl-ester or triglyceride form (see About tab). Amounts are not advised on this page.
Who was studied
General adults; pregnancy and children have their own guidance (see Safety tab).
Limits
Health-agency pages, not trials. Food and supplement are not interchangeable: food brings protein, vitamin D and other nutrients, and people who eat fish tend to have healthier lifestyles (NCCIH).
Why researchers looked
Many people take fish oil to get EPA and DHA when they do not eat much fish.
Traditional use
Eating oily fish is long-standing food advice. Fish oil capsules are a modern way to get the same two fats.
Proposed mechanism Established nutrition
The NHS says long-chain omega-3 helps a baby's nervous system develop during pregnancy and breastfeeding. Other roles of EPA and DHA in the body were not researched for this page.
A proposed mechanism does not show that the effect happens in people.
Fish liver oils (such as cod liver oil) are a different product with vitamins A and D; see Safety tab.
Lowering blood triglycerides
High certaintyTriglycerides are a type of fat in the blood. A 2020 Cochrane review found that raising long-chain omega-3 lowered triglycerides by about 15%, in a way that depended on the amount, with high-certainty evidence. Prescription omega-3 medicines are approved for very high triglycerides. This is a lab marker: it does not by itself show fewer heart attacks.
4 studiesFish-oil capsules in most trials; prescription EPA-only or EPA plus D…
Studies, doses and limits
What the trials found
The Cochrane review (86 trials, 162,796 people) found that increasing long-chain omega-3, mostly from supplement trials, cut triglycerides by about 15% with high-certainty evidence, and had little or no effect on other blood fats or body fat. An American Heart Association advisory says prescription omega-3 at large amounts reduced triglycerides by at least 30% in people with very high levels (500 mg per dL or more) and that EPA plus DHA products raised LDL cholesterol while EPA alone did not. The prescription label says the medicine is an add-on to diet for adults with severe high triglycerides (500 mg per dL or more) and that LDL cholesterol should be monitored. NCCIH says prescription products are not the same as ordinary supplements, so their effects may differ.
Results
A real, reliable lowering of triglycerides. The size depends on the amount and on starting levels. It is a blood marker; lower triglycerides from omega-3 have not been shown to prevent heart attacks in the large trials (see next item).
Effect sizes as reported
About 15% lower triglycerides in the Cochrane review; at least 30% lower with prescription amounts in very high triglycerides (AHA advisory).
Why this rating
High-certainty (GRADE) rating in the Cochrane review for the 15% fall; the larger fall is for prescription products in a different group of patients.
Form and dose studied
Fish-oil capsules in most trials; prescription EPA-only or EPA plus DHA products in the larger-fall trials. Trial amounts are in the studies table.
Who was studied
Adults, with and without high triglycerides. Prescription products are for adults with severe high triglycerides under medical care.
Limits
Marker not outcome. Review mixes supplement and food trials. The prescription statements apply to medicines, not to ordinary fish oil.
Why researchers looked
High triglycerides raise heart risk, and omega-3 fats change how the liver makes and clears them.
Traditional use
Lowering triglycerides is the best-supported use of omega-3, and the one for which prescription products exist.
Proposed mechanism Regulator label hypothesis
The label for a prescription omega-3 medicine says how it works is not completely understood. Possible actions include less fat made in the liver and more activity of the enzyme that clears blood fats.
A proposed mechanism does not show that the effect happens in people.
EPA plus DHA prescription products can raise LDL cholesterol (label, AHA). Atrial fibrillation and bleeding cautions are on the Safety tab. Anyone with high triglycerides should have it managed by a doctor.
Heart attacks, strokes and other heart events
Mixed findingsMany people take fish oil to protect the heart. The largest review (86 trials, 162,796 people) found little or no effect on deaths from any cause, on heart and circulation events overall, or on stroke. It found a possible small drop in coronary heart disease events (low certainty). One purified-EPA prescription drug did lower events in one large trial, but a large trial of a prescription EPA plus DHA product did not.
6 studiesFish-oil capsules in most trials; REDUCE-IT used purified EPA ethyl e…
Studies, doses and limits
What the trials found
Cochrane 2020: all-cause death RR 0.97 (high certainty), cardiovascular events RR 0.96 (high), cardiovascular death RR 0.92 (moderate), coronary heart disease events RR 0.91 (low), stroke RR 1.02 (moderate), arrhythmia RR 0.99 (low). VITAL (25,871 people without known heart disease): no significant fall in major cardiovascular events (HR 0.92, 0.80 to 1.06) or cancer; heart attacks were fewer (HR 0.72, a secondary result). REDUCE-IT (8,179 statin-treated people with high triglycerides): purified EPA ethyl ester, a prescription drug, lowered events (HR 0.75), but more people were hospitalised for atrial fibrillation (3.1% vs 2.1%); it was funded by the drug maker. STRENGTH (13,078 similar people): prescription EPA plus DHA versus corn oil, no difference (HR 0.99), with more stomach side effects. A 2024 review of 15 trials found slightly fewer major events (RR 0.95) and more atrial fibrillation (RR 1.25), and said the benefit came mainly from prescription EPA ethyl ester.
Results
Mixed. Ordinary fish oil capsules have not been shown to prevent heart attacks or strokes in most adults. A small benefit for coronary events is possible. A prescription EPA drug helped one high-risk group in a drug-company trial.
Effect sizes as reported
See text: Cochrane RRs 0.91 to 1.02 depending on outcome; VITAL HR 0.92; REDUCE-IT HR 0.75; STRENGTH HR 0.99; 2024 review RR 0.95.
Why this rating
High-certainty evidence of little or no effect on death and overall events, low-certainty for a small coronary benefit, and large prescription-drug trials that disagree (one positive, drug-maker funded; one null).
Form and dose studied
Fish-oil capsules in most trials; REDUCE-IT used purified EPA ethyl ester and STRENGTH used an EPA plus DHA carboxylic acid prescription product. Amounts are in the studies table.
Who was studied
Adults from healthy to high heart risk; some trials only in people on statins with high triglycerides.
Limits
Different products and amounts across trials. STRENGTH used corn oil as its comparator. Only abstracts were read.
Why researchers looked
People who eat a lot of fish seem to have less heart disease, so researchers tested the oil.
Traditional use
Eating fish for the heart is long-standing advice; the NHS says oily fish may help prevent heart disease.
Proposed mechanism Preliminary mechanism
Not established. Lower triglycerides is one known effect (see above), but the trials read do not show that it explains any heart benefit.
A proposed mechanism does not show that the effect happens in people.
More atrial fibrillation was seen in several large trials; see Safety tab.
Depression
Very low certaintyA 2021 Cochrane review of 35 trials found a small fall in depression scores with omega-3 compared with placebo, but the evidence is very low certainty, the effect is probably too small to matter, and it may be biased toward a benefit. There was no clear difference in remission or response. Omega-3 should not replace depression treatment.
2 studiesOmega-3 products of many types, including fish-oil capsules; trial am…
Studies, doses and limits
What the trials found
The Cochrane review (34 trials, 1,924 people, vs placebo) found depression scores lower by SMD -0.40 (-0.64 to -0.16), roughly 2.5 points on a scale where 3 points is the smallest change that matters; remission OR 1.13 (0.74 to 1.72) and response OR 1.20 (0.80 to 1.79), low certainty. Adverse events were similar (OR 1.27, 0.99 to 1.64, very low certainty). One tiny trial of 40 people compared omega-3 with an antidepressant and could not tell them apart. NCCIH adds that some reviews suggest EPA may work better than DHA and that omega-3 may be best used alongside antidepressants, but that more good trials are needed.
Results
Uncertain, probably a very small effect. People with depression should ask a doctor about proven treatment.
Effect sizes as reported
SMD -0.40 (-0.64 to -0.16) vs placebo, very-low certainty; remission OR 1.13.
Why this rating
The Cochrane authors rate the main result very-low certainty (large differences between trials, bias toward benefit, imprecise).
Form and dose studied
Omega-3 products of many types, including fish-oil capsules; trial amounts varied.
Who was studied
Adults with major depression.
Limits
Heterogeneous trials; possible publication bias; only abstract read.
Why researchers looked
The Cochrane authors say various lines of evidence suggest a role for omega-3 in depression, but that the evidence is far from conclusive.
Traditional use
Fish oil is often marketed for mood. The research does not support it as a treatment on its own.
Proposed mechanism Not established
Not established. Researchers suggest effects on brain cell membranes and inflammation, but no source read shows this explains any benefit.
A proposed mechanism does not show that the effect happens in people.
Side effects were similar to placebo but the estimate is imprecise.
ADHD in children and teenagers
Evidence againstA 2023 Cochrane review of 37 trials found high-certainty evidence that omega-3 and other polyunsaturated fat supplements do not improve parent-rated ADHD symptoms in children and teenagers. Three small trials gave a low-certainty hint of benefit.
2 studiesOmega-3 alone in 19 trials, omega-3 plus omega-6 in 6, omega-6 in 2.
Studies, doses and limits
What the trials found
The review included 37 trials and about 2,374 children. Parent-rated total ADHD symptoms did not differ from placebo (SMD -0.08, -0.24 to 0.07; 16 studies, 1,166 children; high certainty); inattention and hyperactivity also did not differ. A low-certainty analysis of 3 studies (191 children) found more improved with supplements (RR 1.95). Side effects likely did not differ (moderate certainty).
Results
Evidence against a benefit for ADHD symptoms.
Effect sizes as reported
Total symptoms SMD -0.08 (-0.24 to 0.07), high certainty.
Why this rating
High-certainty (GRADE) finding of no effect on the main parent-rated outcome.
Form and dose studied
Omega-3 alone in 19 trials, omega-3 plus omega-6 in 6, omega-6 in 2.
Who was studied
Children and teenagers aged 18 and under diagnosed with ADHD.
Limits
Small trials, short follow-up, varied products.
Why researchers looked
Children with ADHD have been found to have lower blood omega-3, so researchers asked whether adding it would help.
Traditional use
Fish oil is often sold for children's focus. Trials do not back this.
Proposed mechanism Not established
Not established.
A proposed mechanism does not show that the effect happens in people.
Side effects did not differ from placebo.
Pregnancy: early birth and baby development
Moderate certaintyA 2018 Cochrane review of 70 trials found that omega-3 given in pregnancy lowered the chance of preterm birth (high-quality evidence), but made going past 42 weeks more likely. It found very few differences in children's later thinking, vision or language. Fish liver oils such as cod liver oil are a different product and the NHS says to avoid them in pregnancy.
3 studiesOmega-3 long-chain fatty acids as supplements (mostly fish oil) or fo…
Studies, doses and limits
What the trials found
Cochrane 2018 (70 trials, 19,927 women): preterm birth before 37 weeks RR 0.89 (0.81 to 0.97) and before 34 weeks RR 0.58 (0.44 to 0.77), both high-quality evidence; births after 42 weeks RR 1.61 (1.11 to 2.33), moderate quality; low birth weight RR 0.90 (0.82 to 0.99); possible small rise in large babies (RR 1.15, 0.97 to 1.36, not significant). For children, there were very few differences in thinking, vision, language and growth (mostly low or very-low quality). NCCIH reports that a 2016 US government review (AHRQ) of 143 studies found longer pregnancies but no effect on premature birth risk, and a 2020 review found limited evidence for children's thinking skills, so the findings are not fully consistent.
Results
Reviews agree on little proof for children's development. They disagree somewhat on preterm birth. This is a decision for a pregnancy care team, not for self-treatment.
Effect sizes as reported
Preterm birth <37 weeks RR 0.89; <34 weeks RR 0.58; >42 weeks RR 1.61.
Why this rating
Cochrane rates preterm birth high quality, but another large review (AHRQ, as reported by NCCIH) did not find the same, and child outcomes are low quality.
Form and dose studied
Omega-3 long-chain fatty acids as supplements (mostly fish oil) or food; amounts varied.
Who was studied
Pregnant women, mostly in higher-income countries; nearly half at higher risk.
Limits
Mixed supplements and foods; fish liver oils not tested; some attrition bias.
Why researchers looked
Eating fish in pregnancy has been linked to longer pregnancies and better birth outcomes (Cochrane background), and the NHS says omega-3 helps a baby's nervous system develop.
Traditional use
The NHS says long-chain omega-3 is important in pregnancy because it helps a baby's nervous system develop; its advice is to eat oily fish within limits.
Proposed mechanism Preliminary mechanism
Not established in the sources read.
A proposed mechanism does not show that the effect happens in people.
Pregnancy cautions and the NHS warning on fish liver oils are on the Safety tab.
Joint pain in rheumatoid arthritis
Low certaintyA 2022 review of 30 trials in inflammatory joint diseases, mostly rheumatoid arthritis, found less pain and fewer swollen and tender joints with omega-3 and other polyunsaturated fat supplements. It was most evident with fish-source oils and mostly in trials of large amounts. The evidence is low quality, and it does not replace arthritis medicines.
2 studiesOral omega-3 (fish or plant source) and omega-6 supplements; mostly l…
Studies, doses and limits
What the trials found
The meta-analysis (30 randomised trials, 710 treated and 710 control) found significant improvements in pain, swollen and tender joint counts, the Disease Activity Score in 28 joints, and a disability questionnaire; the blood marker ESR fell but CRP did not. More measures improved with animal-source (fish) than plant-source oils. Most studies used large daily amounts (see studies table). NCCIH also reports a 2021 review of 12 studies that found less pain but rated the evidence low.
Results
Possible modest help with symptoms, with low-quality evidence, as an extra to prescribed treatment. NCCIH says not to change prescribed arthritis medicines.
Effect sizes as reported
Standardised mean differences favoured supplements (values not in the abstract).
Why this rating
Many small trials of mixed quality; mostly large amounts; includes omega-6 trials.
Form and dose studied
Oral omega-3 (fish or plant source) and omega-6 supplements; mostly large daily amounts (see studies table).
Who was studied
Adults with inflammatory rheumatic diseases, mostly rheumatoid arthritis.
Limits
Mixed quality, short trials, abstract only.
Why researchers looked
Omega-3 is often tested for a possible effect on joint inflammation.
Traditional use
Fish oil has long been used for sore joints.
Proposed mechanism Not established
Not established in the sources read.
A proposed mechanism does not show that the effect happens in people.
Check with your rheumatology team before adding a supplement.
Memory and dementia
Low certaintyA 2022 review found that eating fish up to about two portions a week was linked to a lower risk of Alzheimer's disease, and that raising EPA and DHA helped executive function (planning and attention) but not overall thinking scores. Fish intake studies are observational, so they cannot prove fish itself protects the brain.
2 studiesFish intake (food) and EPA/DHA supplements; amounts varied.
Studies, doses and limits
What the trials found
The review combined observational studies of fish intake and trials of EPA/DHA supplements. Among studies with low or moderate risk of bias, fish intake of up to 2 portions a week was linked to 10% lower all-cause dementia (0.79 to 1.02, not statistically significant, 5 studies) and 30% lower Alzheimer's risk (0.54 to 0.89, 3 studies). Changes in EPA and DHA status improved executive function but not overall cognitive performance. NCCIH reports that supplements had no effect in people already diagnosed with Alzheimer's disease.
Results
Early and mixed. Not proven to prevent memory loss, and no benefit in people already diagnosed.
Effect sizes as reported
Alzheimer's 30% lower with fish intake (0.54 to 0.89); dementia 10% lower (not significant).
Why this rating
Low: observational fish-intake results and few supplement trials.
Form and dose studied
Fish intake (food) and EPA/DHA supplements; amounts varied.
Who was studied
Older adults, with and without memory problems.
Limits
Fish intake is not fish oil; few studies; observational data cannot show cause.
Why researchers looked
Observational studies suggest people who eat more fish keep their memory longer.
Traditional use
"Fish is brain food" is an old saying; the research is early.
Proposed mechanism Not established
Not established.
A proposed mechanism does not show that the effect happens in people.
No special safety signal beyond those on the Safety tab.
Age-related macular degeneration (AMD)
Evidence againstIn the AREDS2 trial of 4,203 people at risk, adding DHA plus EPA to the standard eye vitamin formula did not slow progression to advanced AMD. Other studies read by NCCIH also have not shown a benefit.
2 studiesDHA plus EPA capsules added to the AREDS vitamin formula.
Studies, doses and limits
What the trials found
AREDS2 randomised 4,203 people aged 50 to 85 at risk of advanced AMD to DHA plus EPA, lutein plus zeaxanthin, both, or placebo, on top of an eye vitamin formula. Five-year progression to advanced AMD was 31% with placebo and 31% with DHA plus EPA (HR 0.97, 98.7% CI 0.82 to 1.16). NCCIH says other omega-3 studies have not shown a benefit on AMD progression.
Results
Evidence against a benefit of omega-3 for slowing AMD in people at risk.
Effect sizes as reported
HR 0.97 (98.7% CI 0.82 to 1.16) for DHA plus EPA vs placebo.
Why this rating
A large randomised trial found no effect; NCCIH reports other studies agree.
Form and dose studied
DHA plus EPA capsules added to the AREDS vitamin formula.
Who was studied
People with large drusen (early or intermediate AMD signs).
Limits
One large trial; everyone also took the AREDS vitamins.
Why researchers looked
AREDS2 asked this because observational data suggested that eating more omega-3-rich food might lower AMD risk.
Traditional use
Omega-3 is often added to eye supplements.
Proposed mechanism Not established
Not established.
A proposed mechanism does not show that the effect happens in people.
None specific to this use.
Dry eye
Mixed findingsNCCIH reports that a one-year NIH-funded trial of 535 people with moderate to severe dry eye (the DREAM study) found omega-3 no better than placebo, while a 2022 review of 8 small studies suggested symptoms may improve. The original DREAM paper could not be read for this page.
1 studiesOmega-3 capsules and, in two studies, eye drops.
Studies, doses and limits
What the trials found
This item rests on the NCCIH page only: DREAM (535 people, 12 months) found no benefit over placebo, a follow-up of 43 people found no difference after another 12 months, and a 2022 review of 8 studies (1,107 people; capsules or eye drops) suggested improvement but noted differing sizes, lengths and possible bias. The DREAM paper and the 2022 review abstract were not read.
Results
Mixed; the largest trial reported no benefit.
Effect sizes as reported
Not read.
Why this rating
One large null trial versus small positive studies; only a secondary report was read.
Form and dose studied
Omega-3 capsules and, in two studies, eye drops.
Who was studied
Adults with dry eye disease.
Limits
Not verified against the original papers.
Why researchers looked
Small studies suggested omega-3 might ease dry eye symptoms (NCCIH).
Traditional use
Omega-3 is a common over-the-counter suggestion for dry eyes.
Proposed mechanism Not established
Not established.
A proposed mechanism does not show that the effect happens in people.
None specific.
Cancer prevention
Evidence againstIn the VITAL trial of 25,871 people, marine omega-3 capsules did not lower the number of cancers diagnosed or deaths from cancer compared with placebo.
2 studiesMarine omega-3 capsules.
Studies, doses and limits
What the trials found
VITAL (median 5.3 years): invasive cancer was diagnosed in 820 people taking omega-3 and 797 taking placebo (HR 1.03, 0.93 to 1.13); death from cancer HR 0.97 (0.79 to 1.20). A 2024 meta-analysis of 15 heart trials also found no overall difference in cancer.
Results
No benefit shown.
Effect sizes as reported
Cancer HR 1.03 (0.93 to 1.13).
Why this rating
Large randomised trial with no effect; a review of heart trials agrees. Follow-up of about five years may be too short for cancer.
Form and dose studied
Marine omega-3 capsules.
Who was studied
Older adults without prior cancer or heart disease.
Limits
Five-year follow-up; one large trial.
Why researchers looked
Observational studies had linked fish intake to lower cancer risk.
Proposed mechanism Not established
Not established.
A proposed mechanism does not show that the effect happens in people.
None specific.
Connections to the rest of health
How Fish oil connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.
Explore every connection: goals, body systems, organs, symptoms, genes
A. Wellness goals
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Heart Health | High certainty | A source of EPA and DHA (and how food compares): Fish oil is a supplement made from the oil of fish. It supplies two long-chain omega-3 fats, EPA and DHA. The same fats come from seafood, especially oily fish such as salmon, mackerel, sardines and herring. NCCIH says that for some conditions the evidence for eating seafood is stronger than the evidence for supplements, and that other nutrients in fish, or eating fish instead of less healthy foods, may play a part. | 19 20 | |
| Brain Health | High certainty | A source of EPA and DHA (and how food compares): Fish oil is a supplement made from the oil of fish. It supplies two long-chain omega-3 fats, EPA and DHA. The same fats come from seafood, especially oily fish such as salmon, mackerel, sardines and herring. NCCIH says that for some conditions the evidence for eating seafood is stronger than the evidence for supplements, and that other nutrients in fish, or eating fish instead of less healthy foods, may play a part. | 19 20 | |
| Heart Health | Demonstrated clinical effect | High certainty | Lowering blood triglycerides: Triglycerides are a type of fat in the blood. A 2020 Cochrane review found that raising long-chain omega-3 lowered triglycerides by about 15%, in a way that depended on the amount, with high-certainty evidence. Prescription omega-3 medicines are approved for very high triglycerides. This is a lab marker: it does not by itself show fewer heart attacks. | 1 16 18 19 |
| Heart Health | Mixed findings | Heart attacks, strokes and other heart events: Many people take fish oil to protect the heart. The largest review (86 trials, 162,796 people) found little or no effect on deaths from any cause, on heart and circulation events overall, or on stroke. It found a possible small drop in coronary heart disease events (low certainty). One purified-EPA prescription drug did lower events in one large trial, but a large trial of a prescription EPA plus DHA product did not. | 1 9 5 11 17 19 | |
| Mood Balance | Very low certainty | Depression: A 2021 Cochrane review of 35 trials found a small fall in depression scores with omega-3 compared with placebo, but the evidence is very low certainty, the effect is probably too small to matter, and it may be biased toward a benefit. There was no clear difference in remission or response. Omega-3 should not replace depression treatment. | 4 19 | |
| Focus Memory | Evidence against | ADHD in children and teenagers: A 2023 Cochrane review of 37 trials found high-certainty evidence that omega-3 and other polyunsaturated fat supplements do not improve parent-rated ADHD symptoms in children and teenagers. Three small trials gave a low-certainty hint of benefit. | 7 19 | |
| Womens Wellness | Moderate certainty | Pregnancy: early birth and baby development: A 2018 Cochrane review of 70 trials found that omega-3 given in pregnancy lowered the chance of preterm birth (high-quality evidence), but made going past 42 weeks more likely. It found very few differences in children's later thinking, vision or language. Fish liver oils such as cod liver oil are a different product and the NHS says to avoid them in pregnancy. | 10 19 20 | |
| Joint Support | Low certainty | Joint pain in rheumatoid arthritis: A 2022 review of 30 trials in inflammatory joint diseases, mostly rheumatoid arthritis, found less pain and fewer swollen and tender joints with omega-3 and other polyunsaturated fat supplements. It was most evident with fish-source oils and mostly in trials of large amounts. The evidence is low quality, and it does not replace arthritis medicines. | 15 19 | |
| Brain Health | Low certainty | Memory and dementia: A 2022 review found that eating fish up to about two portions a week was linked to a lower risk of Alzheimer's disease, and that raising EPA and DHA helped executive function (planning and attention) but not overall thinking scores. Fish intake studies are observational, so they cannot prove fish itself protects the brain. | 8 19 | |
| Memory Support | Low certainty | Memory and dementia: A 2022 review found that eating fish up to about two portions a week was linked to a lower risk of Alzheimer's disease, and that raising EPA and DHA helped executive function (planning and attention) but not overall thinking scores. Fish intake studies are observational, so they cannot prove fish itself protects the brain. | 8 19 | |
| Healthy Aging | Evidence against | Age-related macular degeneration (AMD): In the AREDS2 trial of 4,203 people at risk, adding DHA plus EPA to the standard eye vitamin formula did not slow progression to advanced AMD. Other studies read by NCCIH also have not shown a benefit. | 2 19 | |
| Healthy Aging | Mixed findings | Dry eye: NCCIH reports that a one-year NIH-funded trial of 535 people with moderate to severe dry eye (the DREAM study) found omega-3 no better than placebo, while a 2022 review of 8 small studies suggested symptoms may improve. The original DREAM paper could not be read for this page. | 19 | |
| Preventive Wellness | Evidence against | Cancer prevention: In the VITAL trial of 25,871 people, marine omega-3 capsules did not lower the number of cancers diagnosed or deaths from cancer compared with placebo. | 9 17 |
B. Body systems
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Heart Circulation | Biological association | High certainty | Studied for: A source of EPA and DHA (and how food compares) Studied for: Lowering blood triglycerides | 19 20 1 16 18 9 5 11 17 |
| Nervous System | Biological association | High certainty | Studied for: A source of EPA and DHA (and how food compares) Studied for: ADHD in children and teenagers | 19 20 7 10 8 |
| Cardiovascular System | Biological association | High certainty | Studied for: Lowering blood triglycerides Studied for: Heart attacks, strokes and other heart events | 1 16 18 19 9 5 11 17 |
| Stress Mood | Biological association | Very low certainty | Studied for: Depression | 4 19 |
| Brain Focus | Biological association | Very low certainty | Studied for: Depression Studied for: ADHD in children and teenagers | 4 19 7 8 |
| Reproductive System | Biological association | Moderate certainty | Studied for: Pregnancy: early birth and baby development | 10 19 20 |
| Bones Joints Muscles | Biological association | Low certainty | Studied for: Joint pain in rheumatoid arthritis | 15 19 |
| Eyes | Biological association | Evidence against | Studied for: Age-related macular degeneration (AMD) Studied for: Dry eye | 2 19 |
| Whole Body Balance | Biological association | Evidence against | Studied for: Cancer prevention | 9 17 |
E. Health conditions
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Atrial fibrillation | Adverse effect or risk | Documented risk | More atrial fibrillation in large trials, higher with larger amounts. Preparation or compound: Marine omega-3 supplements |
6 18 |
| Longer bleeding time | Drug or supplement interaction | Documented risk | Label: may prolong bleeding time; monitor with blood thinners. Preparation or compound: Omega-3 acids |
18 |
| Fish or shellfish allergy | Regulator label | Label advises caution; risk not known. Preparation or compound: Fish oil |
18 | |
| High triglycerides | Clinical trial evidence | Omega-3 lowered triglycerides by about 15% in a Cochrane review. Preparation or compound: Fish oil |
1 16 | |
| ADHD | Clinical trial evidence against | High-certainty evidence of no effect on parent-rated symptoms. Preparation or compound: Omega-3 supplements |
7 |
I. Biomarkers
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Blood triglycerides | Biological association | High certainty | Measured in trials: lower. A lab change is not the same as a health benefit. | 1 16 |
| Major cardiovascular events (heart attack, stroke, heart death) | Biological association | Mixed findings | Measured in trials: little or no change for ordinary fish oil; lower in one prescription EPA trial. A lab change is not the same as a health benefit. | 1 9 5 11 |
| Depression rating scores | Biological association | Very low certainty | Measured in trials: slightly lower (very-low certainty). A lab change is not the same as a health benefit. | 4 |
| Preterm birth (before 37 weeks) | Biological association | Moderate certainty | Measured in trials: lower. A lab change is not the same as a health benefit. | 10 19 |
K. Biological pathways
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Vitamin D | Preliminary mechanism | Human | The VITAL trial gave vitamin D3 and marine omega-3 together in a two-by-two design; cod liver oil also contains vitamin D. | 9 19 |
| Vitamin A | Preliminary mechanism | Human | Fish liver oils carry vitamin A; the NHS limits it in pregnancy. | 20 |
L. Active compounds
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| EPA (eicosapentaenoic acid) | Biological association | Human | One of the two omega-3 fats most research is about (NCCIH). Purified EPA ethyl ester as a prescription drug lowered heart events in REDUCE-IT. | 19 18 5 |
| DHA (docosahexaenoic acid) | Biological association | Human | The other main omega-3 fat; the NHS and NCCIH link omega-3 intake to a baby's nervous system development. AREDS2 tested DHA plus EPA for AMD without benefit. | 19 20 2 |
| Ethyl ester form | Biological association | Human | A form used in concentrated products and prescription medicines. The label says EPA and DHA were absorbed from ethyl esters, with EPA rising in a dose-dependent way. | 18 14 |
| Triglyceride, free fatty acid and phospholipid forms | Biological association | Human | A 2013 review says the chemical form affects absorption but does not give a ranking. | 14 |
Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 26, 2026).
Evidence at a glance: what the research found for 11 outcomes
Each outcome below is one thing researchers measured. Certainty is how far the evidence can be trusted, not how well it works. The full studies are on the next tab.
The evidence
The research centre for Fish oil. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.
Evidence by outcome
Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).
How we rate evidence
High certainty
Several well-run trials or reviews agree; further research is unlikely to change the picture much.
Moderate certainty
Good trials point the same way, but some doubt remains.
Low certainty
Small, short or inconsistent trials. The finding could change with better research.
Very low certainty
Very little or very weak human data. Treat as a possibility only.
Mixed findings
Trials or reviews disagree with each other.
Not enough evidence
Not enough human research to say either way.
Evidence against
Good research found no benefit, or found harm.
We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We started from our existing fish oil summary, then read the NCCIH omega-3 page, the NHS fish page and a US prescription omega-3 label, and re-read PubMed abstracts for reviews and trials. Only abstracts were read for studies. The NIH Office of Dietary Supplements page and the EFSA opinion were blocked and are marked unread.
Study library: every study we checked 20
| Study | Design | People | Product, dose, length | Result |
|---|---|---|---|---|
| Abdelhamid 2020 Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev · PMID 32114706 · DOI |
Systematic review meta analysis |
162796 86 randomised trials lasting 12 to 88 months in adults at varying heart risk; most (65) used capsules, others used fish-rich foods or dietary advice |
Long-chain omega-3 (EPA and DHA) and plant omega-3 (ALA); mostly fish-oil capsules Capsules; some food and advice trials Ranged from 0.5 g a day to more than 5 g a day of long-chain omega-3 (19 trials gave at least 3 g) 12 to 88 months · vs Usual or lower intake, or placebo |
Raising long-chain omega-3 made little or no difference to deaths, heart events, stroke or rhythm problems. It may slightly lower deaths and events from coronary heart disease, and it lowered triglycerides by about 15% in a dose-dependent way (high certainty). All-cause death RR 0.97; cardiovascular events RR 0.96; cardiovascular death RR 0.92; coronary heart disease events RR 0.91; stroke RR 1.02; arrhythmia RR 0.99; triglycerides about 15% lower (All-cause death 0.93 to 1.01 (high certainty); cardiovascular events 0.92 to 1.01 (high); cardiovascular death 0.86 to 0.99 (moderate); coronary events 0.85 to 0.97 (low); stroke 0.94 to 1.12 (moderate); arrhythmia 0.92 to 1.06 (low)) Methods, limits and fundingOutcomes: All-cause death, heart and circulation events, stroke, rhythm problems, body fat, blood fats Limitations: Only 28 of 86 trials had low risk of bias. Mixes capsules, foods and advice. Mostly high-income countries. Abstract only was read. Funding and conflicts: The authors declare no known conflicts of interest. Read: abstract |
| Age-Related Eye Disease Study 2 Research Group 2013 Lutein + zeaxanthin and omega-3 fatty acids for age-related macular degeneration: the Age-Related Eye Disease Study 2 (AREDS2) randomized clinical trial. JAMA · PMID 23644932 · DOI |
Randomised controlled trial |
4203 People aged 50 to 85 at risk of advanced age-related macular degeneration (AMD) |
DHA plus EPA (also lutein and zeaxanthin in other arms), added to the AREDS vitamin formula Capsules DHA 350 mg plus EPA 650 mg a day as studied in the trial Median 5 years · vs Placebo |
Adding DHA plus EPA did not reduce progression to advanced AMD (31% vs 31% over 5 years). Hazard ratio 0.97 (98.7% CI 0.82 to 1.16) Methods, limits and fundingOutcomes: Progression to advanced AMD Limitations: All took a background vitamin formula, so this tests omega-3 as an extra. Only AMD progression was measured. Funding and conflicts: PubMed lists NIH extramural and intramural research support. Read: abstract |
| Albert 2015 Fish oil supplements in New Zealand are highly oxidised and do not meet label content of n-3 PUFA. Sci Rep · PMID 25604397 · DOI |
Laboratory analysis n/a |
32 32 encapsulated fish oil supplements on the New Zealand market |
Fish oil capsules Capsule · vs Label claims and recommended oxidation limits |
Only 3 of 32 products had as much EPA and DHA as labelled; 69% had less than two thirds of the labelled amount. Most exceeded recommended oxidation levels. Price, best-before date and country of origin did not predict quality. 3 of 32 met or exceeded label; 83% above the recommended peroxide level; 25% above the anisidine limit; 50% above the total oxidation limit; 8% met all limits Methods, limits and fundingOutcomes: EPA and DHA content versus label; oxidation markers Limitations: One country, 2015 market. A later industry-linked study (below) found the opposite using different laboratories. Funding and conflicts: Research support from non-US government sources is listed in PubMed; no conflicts are stated in the abstract. Read: abstract |
| Appleton 2021 Omega-3 fatty acids for depression in adults. Cochrane Database Syst Rev · PMID 34817851 · DOI |
Systematic review meta analysis |
1964 35 randomised trials in adults with major depression (34 vs placebo, 1,924 people; 1 vs an antidepressant, 40 people) |
Omega-3 polyunsaturated fatty acids (various products, including fish-oil types) Capsules and liquids Varied between trials Varied · vs Placebo; one trial against an antidepressant |
A small to modest fall in depression scores versus placebo, judged very-low certainty and unlikely to be clinically meaningful. No clear difference in remission or response. Side effects were similar but imprecise. Depression scores SMD -0.40 (about 2.5 points on the 17-item Hamilton scale; the smallest change that matters is 3 points); remission OR 1.13; response OR 1.20; adverse events OR 1.27 (Scores -0.64 to -0.16; remission 0.74 to 1.72; response 0.80 to 1.79; adverse events 0.99 to 1.64) Methods, limits and fundingOutcomes: Depression scores; remission; response; quality of life; adverse events Limitations: Very-low to low certainty; large differences between trials; the result may be biased toward a benefit. Only one tiny trial against antidepressants. Funding and conflicts: The authors state no conflicts in the abstract (Cochrane). Read: abstract |
| Bhatt 2019 Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia. N Engl J Med · PMID 30415628 · DOI |
Randomised controlled trial |
8179 Adults on a statin with high triglycerides (135 to 499 mg per dL); 70.7% had established cardiovascular disease, the rest had diabetes and other risk factors |
Icosapent ethyl (highly purified EPA ethyl ester), a prescription medicine Prescription capsule (not an ordinary fish oil) 2 g twice a day (4 g a day) as studied in the trial Median 4.9 years · vs Placebo |
Fewer heart and circulation events with icosapent ethyl than placebo. More people were hospitalised for atrial fibrillation or flutter (3.1% vs 2.1%). Serious bleeding was 2.7% vs 2.1% (not statistically different). Main events HR 0.75 (17.2% vs 22.0%); cardiovascular death HR 0.80 (Main events 0.68 to 0.83; cardiovascular death 0.66 to 0.98) Methods, limits and fundingOutcomes: Cardiovascular death, heart attack, stroke, revascularisation, unstable angina; hospital stays for atrial fibrillation; serious bleeding Limitations: Tests a purified EPA-only prescription drug in people already on statins. The result should not be assumed to apply to ordinary fish oil capsules, which mix EPA and DHA. Funding and conflicts: Funded by Amarin Pharma, the maker of the drug. Read: abstract |
| Gencer 2021 Effect of Long-Term Marine ɷ-3 Fatty Acids Supplementation on the Risk of Atrial Fibrillation in Randomized Controlled Trials of Cardiovascular Outcomes: A Systematic Review and Meta-Analysis. Circulation · PMID 34612056 · DOI |
Systematic review meta analysis |
81210 7 large randomised trials of marine omega-3 for heart outcomes (at least 500 people, at least 1 year); trials in people already in atrial fibrillation were left out |
Marine omega-3 (fish-oil type) supplements Capsules 58,939 people were in trials testing 1 g a day or less, 22,271 in trials testing more than 1 g a day Weighted average 4.9 years · vs Placebo or control |
Marine omega-3 was linked to more atrial fibrillation, and the risk was greater in trials that tested larger daily amounts. All trials HR 1.25; trials of 1 g a day or less HR 1.12; trials of more than 1 g a day HR 1.49; rise per extra 1 g a day HR 1.11 (All 1.07 to 1.46; 1 g or less 1.03 to 1.22; more than 1 g 1.04 to 2.15; per 1 g 1.06 to 1.15) Methods, limits and fundingOutcomes: New atrial fibrillation (an irregular heartbeat) Limitations: Atrial fibrillation was reported in different ways across trials. Trials were designed to look at heart outcomes, not heart rhythm. Funding and conflicts: Research support from the US NIH is listed in PubMed; no conflicts are stated in the abstract. Read: abstract |
| Gillies 2023 Polyunsaturated fatty acids (PUFA) for attention deficit hyperactivity disorder (ADHD) in children and adolescents. Cochrane Database Syst Rev · PMID 37058600 · DOI |
Systematic review meta analysis |
2374 37 trials in children and adolescents (18 and under) with ADHD; 36 compared with placebo |
Polyunsaturated fatty acids: 19 trials used omega-3 alone, 6 omega-3 plus omega-6, 2 omega-6 Supplements Varied 2 weeks to 6 months · vs Placebo, or the same other treatment in both groups |
High-certainty evidence of no effect on parent-rated total ADHD symptoms, inattention or hyperactivity. A low-certainty result in 3 small trials suggested more children improved. Side effects were no different. Total symptoms SMD -0.08; inattention SMD -0.01; hyperactivity SMD 0.09; improved vs placebo RR 1.95 (low certainty, 3 studies) (Total symptoms -0.24 to 0.07 (16 studies, 1,166 children); inattention -0.20 to 0.17; hyperactivity -0.04 to 0.23; improved 1.47 to 2.60) Methods, limits and fundingOutcomes: Parent-rated ADHD symptoms, inattention, hyperactivity, side effects Limitations: Small trials, short follow-up, and very different products and selection criteria. Funding and conflicts: One author is a former Cochrane editor but was not involved in editing this review; no other conflicts stated. Read: abstract |
| Kosti 2022 Fish intake, n-3 fatty acid body status, and risk of cognitive decline: a systematic review and a dose-response meta-analysis of observational and experimental studies. Nutr Rev · PMID 34605891 · DOI |
Systematic review meta analysis |
Observational studies of fish intake and dementia, and randomised trials of EPA/DHA supplements on thinking test results | Fish intake (observational) and EPA/DHA supplements (trials) Food and supplements Up to 2 portions of fish a week in the observational analysis Varied · vs Lower or no fish intake; placebo |
Eating up to about 2 portions of fish a week was linked to lower Alzheimer's risk and, less clearly, lower all-cause dementia risk. Raising EPA/DHA status helped executive function but not overall thinking performance. All-cause dementia 10% lower (not statistically significant); Alzheimer's disease 30% lower (Dementia 0.79 to 1.02 (5 studies); Alzheimer's 0.54 to 0.89 (3 studies)) Methods, limits and fundingOutcomes: All-cause dementia, Alzheimer's disease, executive function, overall cognitive performance Limitations: Fish intake results are observational, so they cannot prove cause. Few studies. Abstract only was read. Funding and conflicts: No conflicts are stated in the abstract. Read: abstract |
| Manson 2019 Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer. N Engl J Med · PMID 30415637 · DOI |
Randomised controlled trial |
25871 Men aged 50 and over and women aged 55 and over in the USA, not selected for heart disease; 5,106 were Black participants |
Marine n-3 (omega-3) capsules, with or without vitamin D3 (two-by-two design) Capsule 1 g a day of marine n-3 (and 2,000 IU a day of vitamin D3 in the other arm) as studied in the trial Median 5.3 years · vs Placebo |
No lower rate of major cardiovascular events or of cancer than placebo. Heart attacks were less common (a secondary result). No extra bleeding or other serious side effects were seen. Major cardiovascular events HR 0.92; cancer HR 1.03; total heart attack HR 0.72; stroke HR 1.04; death from any cause HR 1.02 (Major events 0.80 to 1.06; cancer 0.93 to 1.13; heart attack 0.59 to 0.90; stroke 0.83 to 1.31; any-cause death 0.90 to 1.15) Methods, limits and fundingOutcomes: Major cardiovascular events; invasive cancer; heart attack; stroke; death; bleeding Limitations: Heart attack was a secondary result and the main result was not significant. Healthy older adults, so it does not apply to people with known heart disease. Funding and conflicts: Funded by the National Institutes of Health and others. Read: abstract |
| Middleton 2018 Omega-3 fatty acid addition during pregnancy. Cochrane Database Syst Rev · PMID 30480773 · DOI |
Systematic review meta analysis |
19927 70 randomised trials in pregnant women at low, mixed or high risk of poor outcomes |
Omega-3 long-chain fatty acids as supplements (mostly fish oil) or food Capsules and food Varied During pregnancy · vs Placebo or no omega-3 |
Preterm birth before 37 weeks and before 34 weeks were less common (high-quality evidence). Pregnancy was longer and more babies went past 42 weeks (moderate quality). Few differences in children's thinking, vision, language or growth, mostly low-quality evidence. Preterm birth <37 weeks RR 0.89; <34 weeks RR 0.58; past 42 weeks RR 1.61; low birth weight RR 0.90; large for gestational age RR 1.15 (not significant) (<37 weeks 0.81 to 0.97; <34 weeks 0.44 to 0.77; >42 weeks 1.11 to 2.33; low birth weight 0.82 to 0.99; LGA 0.97 to 1.36) Methods, limits and fundingOutcomes: Preterm birth, birth weight, length of pregnancy, baby and mother outcomes, child development Limitations: Mixed risk of bias (some attrition). Trials mix supplements and foods. Child outcomes are mostly low quality. This review does not test fish liver oils. Funding and conflicts: The conflict statement lists grant funding to one author's institution; the funder is cut off in the text read. No sponsor is shown in the abstract. Read: abstract |
| Nicholls 2020 Effect of High-Dose Omega-3 Fatty Acids vs Corn Oil on Major Adverse Cardiovascular Events in Patients at High Cardiovascular Risk: The STRENGTH Randomized Clinical Trial. JAMA · PMID 33190147 · DOI |
Randomised controlled trial |
13078 Statin-treated adults at high cardiovascular risk with high triglycerides and low HDL cholesterol; 70% had diabetes |
Omega-3 carboxylic acid (EPA plus DHA), a prescription formulation Prescription capsule 4 g a day as studied in the trial Stopped early; 1,384 events had occurred · vs Corn oil (meant as an inert comparator) |
No difference in the main outcome (12.0% vs 12.2%). Stomach side effects were more common with omega-3 (24.7% vs 14.7%). The trial stopped early because benefit looked unlikely. Main outcome HR 0.99 (0.90 to 1.09) Methods, limits and fundingOutcomes: Cardiovascular death, heart attack, stroke, revascularisation, unstable angina; stomach side effects Limitations: Corn oil was chosen as an inert comparator; the abstract does not test whether it is truly neutral. Prescription formulation at a high amount, not an ordinary fish oil. Funding and conflicts: The abstract lists payments to authors from several drug companies, including AstraZeneca, and one author founded the company that developed the tested product. The sponsor is not named in the abstract. Read: abstract |
| Nichols 2016 Australian and New Zealand Fish Oil Products in 2016 Meet Label Omega-3 Claims and Are Not Oxidized. Nutrients · PMID 27827947 · DOI |
Laboratory analysis n/a |
10 10 fish oil capsule products bought in Melbourne in 2016 (5 standard, 5 concentrates) |
Fish oil capsules Capsule · vs Label claims and recommended oxidation limits |
All 10 products met or exceeded their label claims (EPA plus DHA averaged 109% of label) and all met the peroxide limit; 8 of 10 met the anisidine limit, the other two contained flavourings that interfere with the test. EPA plus DHA averaged 109% of label (range 99% to 119%); peroxide value met in 10 of 10 Methods, limits and fundingOutcomes: Omega-3 content versus label; oxidation markers Limitations: Only 10 products. The abstract says the paper was written to assist industry; the authors state no conflict of interest. Funding and conflicts: The abstract says the study aims to assist industry; the authors state no conflict of interest. Read: abstract |
| Pasini 2022 Assessment of Lipid Quality in Commercial Omega-3 Supplements Sold in the French Market. Biomolecules · PMID 36291569 · DOI |
Laboratory analysis n/a |
20 20 unflavoured omega-3 supplements sold in France |
Omega-3 supplements Various · vs Label claims and industry (GOED) oxidation limits |
Only 2.5% of the supplements did not meet their label claim for omega-3 content, and all complied with the industry oxidation limits. All 20 products within oxidation limits; 2.5% fell short of label claims Methods, limits and fundingOutcomes: Fatty acid content versus label; oxidation markers Limitations: Only 20 products; not limited to fish oil. The oxidation limits come from an industry group (GOED). Funding and conflicts: The authors declare no conflicts of interest. Read: abstract |
| Schuchardt 2013 Bioavailability of long-chain omega-3 fatty acids. Prostaglandins Leukot Essent Fatty Acids · PMID 23676322 · DOI |
Narrative review |
Review of studies on how EPA and DHA are absorbed | EPA and DHA in different chemical forms (ethyl esters, triglycerides, phospholipids, free fatty acids) · vs Different forms and ways of taking |
Absorption varies with the chemical form, with whether the capsule is taken with food and how much fat the food contains, and with how the product is made (for example emulsified). The authors say bioavailability has been neglected and may explain neutral results in some trials, and call for systematic study. Not applicable (narrative review) Methods, limits and fundingOutcomes: Absorption (bioavailability) of EPA and DHA Limitations: A narrative review; the abstract gives no numbers and does not rank forms. Abstract only was read. Funding and conflicts: Not stated in the abstract. Read: abstract |
| Sigaux 2022 Impact of type and dose of oral polyunsaturated fatty acid supplementation on disease activity in inflammatory rheumatic diseases: a systematic literature review and meta-analysis. Arthritis Res Ther · PMID 35526074 · DOI |
Systematic review meta analysis |
1420 30 randomised trials (710 treated, 710 controls) in inflammatory rheumatic diseases, most in rheumatoid arthritis |
Oral polyunsaturated fatty acids (omega-3 from animal and plant sources, and omega-6) Oral supplements Most studies used more than 2 g a day Subgroups: 3 to 6 months did best · vs Control (placebo or usual) |
Less pain and fewer swollen and tender joints, and lower disease activity scores, with supplementation. Erythrocyte sedimentation rate fell but C-reactive protein did not. More measures improved with animal-source (fish) than plant-source oils. Standardised mean differences favouring supplements (exact values not in the abstract) Methods, limits and fundingOutcomes: Pain, swollen and tender joint counts, disease activity scores, questionnaire scores, blood inflammation markers Limitations: Trials of mixed quality, mostly high amounts. Includes omega-6 trials. Abstract only was read. Funding and conflicts: The authors state no competing interests; several report consulting fees from drug companies. Read: abstract |
| Skulas-Ray 2019 Omega-3 Fatty Acids for the Management of Hypertriglyceridemia: A Science Advisory From the American Heart Association. Circulation · PMID 31422671 · DOI |
Consensus statement |
Adults with high or very high triglycerides (American Heart Association science advisory) | Prescription omega-3 fatty acids (EPA plus DHA, or EPA only) Prescription capsules Pharmacological amounts above 3 g a day of EPA plus DHA, as discussed in the advisory |
In very high triglycerides, prescription EPA plus DHA reduces triglycerides by at least 30% while raising LDL cholesterol; EPA alone did not raise LDL. The advisory concludes prescription omega-3 is an effective and safe option for lowering triglycerides. Triglycerides at least 30% lower in very high triglycerides (prescription) Methods, limits and fundingOutcomes: Triglycerides, LDL cholesterol, other blood fats, heart events Limitations: An expert advisory, not a new trial. It is about prescription products at amounts above ordinary supplements. Funding and conflicts: Written by American Heart Association experts; individual author conflicts are not shown in the abstract. Read: abstract |
| Yan 2024 Efficacy and Safety of Omega-3 Fatty Acids in the Prevention of Cardiovascular Disease: A Systematic Review and Meta-analysis. Cardiovasc Drugs Ther · PMID 36103100 · DOI |
Systematic review meta analysis |
15 randomised trials of omega-3 for preventing cardiovascular disease (number of people not given in the abstract) | Several omega-3 types: prescription EPA ethyl ester, EPA plus DHA ethyl esters, and others Capsules Varied; meta-regression by amount was done Varied · vs Control (placebo or usual care) |
Slightly fewer major cardiovascular events, heart attacks and cardiovascular deaths. More atrial fibrillation. No clear differences in heart failure, stroke, death from any cause, stomach problems, bleeding or cancer overall. The authors say the heart benefit came mainly from prescription EPA ethyl ester, and that prescription EPA ethyl ester had a higher bleeding risk. Major events RR 0.95; heart attack RR 0.90; cardiovascular death RR 0.94; atrial fibrillation RR 1.25 (Major events 0.91 to 0.99; heart attack 0.83 to 0.98; cardiovascular death 0.88 to 0.99; atrial fibrillation 1.10 to 1.41) Methods, limits and fundingOutcomes: Major cardiovascular events, heart attack, heart failure, atrial fibrillation, stroke, death; stomach problems, bleeding, cancer Limitations: Only 15 trials, with different omega-3 products. Abstract only was read. It reaches a slightly more favourable result than the 2020 Cochrane review, mainly because of the prescription EPA trials. Funding and conflicts: PubMed lists non-US government research support; no conflicts are stated in the abstract. Read: abstract |
| s-dailymed-omega3-ee DailyMed: prescribing information, omega-3-acid ethyl esters capsules (Strides Pharma; revised 05/2026) · Source |
Regulator statement n/a |
Methods, limits and fundingRead: full-text | ||
| s-nccih-omega3 NCCIH: Omega-3 Supplements: What You Need To Know (last updated November 2024) · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text | ||
| s-nhs-fish NHS: Fish and shellfish (page last reviewed 26 June 2026) · Source |
Health agency n/a |
Methods, limits and fundingRead: full-text |
What we do not know yet
- Amounts of EPA and DHA per portion of fish could not be read (the USDA table was not reachable).
- The NIH Office of Dietary Supplements fact sheet and the EFSA opinion could not be read, so no official upper intake limit is quoted as verified.
- The DREAM dry-eye trial paper was not read; the dry-eye finding relies on NCCIH.
- No trial was read comparing food omega-3 with fish oil pills directly.
- Pollutants in fish oil capsules and warfarin blood-test effects were not researched.
How new research is added
New studies are found by a saved PubMed search and placed in a review queue before the page changes.
Lab markers
What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".
Metabolic 1
Blood triglycerides
Lower in trials
A type of fat in the blood, measured after fasting. High levels raise heart risk.
High certaintyResults and what it means
Why it was measured
Omega-3 fats lower triglycerides, and prescription products are approved for very high levels.
Statistical vs. clinical meaning
A reliable marker change. It does not by itself prove fewer heart attacks.
Safety implication
EPA plus DHA prescription products can raise LDL cholesterol; ask a doctor if triglycerides are high.
| Study | Result | People | Product |
|---|---|---|---|
| 1 | About 15% lower triglycerides, dose-dependent (high certainty) | Adults in many trials, mostly supplement trials | Long-chain omega-3 (EPA and DHA), mostly fish-oil capsules |
| 16 | At least 30% lower triglycerides in very high triglycerides; LDL cholesterol rose with EPA plus DHA but not with EPA alone | Adults with triglycerides of 500 mg per dL or more | Prescription omega-3 at amounts above ordinary supplements |
Other 3
Major cardiovascular events (heart attack, stroke, heart death)
Little or no change for ordinary fish oil; lower in one prescription EPA trial in trials
A combined count of heart attacks, strokes and deaths from heart causes.
Mixed findingsResults and what it means
Why it was measured
This is the outcome that matters most to people taking fish oil for the heart.
Statistical vs. clinical meaning
Ordinary fish oil: no clear effect. Prescription EPA: benefit in one funded trial, not matched by the other prescription trial.
Safety implication
More atrial fibrillation in several trials; see Safety tab.
| Study | Result | People | Product |
|---|---|---|---|
| 9 | HR 0.92 (0.80 to 1.06), not significant | 25,871 adults without known heart disease | Marine omega-3 capsules vs placebo |
| 5 | HR 0.75 (0.68 to 0.83) for the main combined outcome | 8,179 statin-treated adults with high triglycerides | Prescription purified EPA ethyl ester vs placebo |
| 11 | HR 0.99 (0.90 to 1.09), no difference | 13,078 statin-treated adults at high risk | Prescription EPA plus DHA vs corn oil |
| 1 | Cardiovascular events RR 0.96 (0.92 to 1.01), high certainty of little or no effect | 86 trials, 162,796 adults | Long-chain omega-3, mostly capsules |
Depression rating scores
Slightly lower (very-low certainty) in trials
Scores on questionnaires such as the Hamilton Depression Rating Scale, filled in by a clinician.
Very low certaintyResults and what it means
Why it was measured
To see whether omega-3 reduces depressive symptoms.
Statistical vs. clinical meaning
Probably too small to matter, and may be biased toward benefit.
Safety implication
Side effects were similar to placebo but imprecise.
| Study | Result | People | Product |
|---|---|---|---|
| 4 | SMD -0.40 (-0.64 to -0.16), about 2.5 Hamilton points; the smallest important change is 3 points | 33 trials, 1,848 adults with major depression | Omega-3 supplements vs placebo |
Preterm birth (before 37 weeks)
Lower in trials
A baby born before 37 weeks of pregnancy.
Moderate certaintyResults and what it means
Why it was measured
Omega-3 has been tested to see whether it lengthens pregnancy.
Statistical vs. clinical meaning
Cochrane rates this high quality; another review reported by NCCIH did not agree, so we say moderate.
Safety implication
More births after 42 weeks (RR 1.61).
| Study | Result | People | Product |
|---|---|---|---|
| 10 | RR 0.89 (0.81 to 0.97) | 26 trials, 10,304 women | Omega-3 long-chain fatty acids vs none |
Safety
What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.
Main points to know 4
- Fish oil can raise the chance of an irregular heartbeat (atrial fibrillation). A 2021 review of 7 large trials (81,210 people) found marine omega-3 supplements were linked to more atrial fibrillation (HR 1.25), and the risk looked higher in trials that tested larger daily amounts. A 2024 review of 15 trials also found more atrial fibrillation (RR 1.25). In REDUCE-IT, hospital stays for atrial fibrillation or flutter were 3.1% with a prescription EPA drug and 2.1% with placebo. The prescription omega-3 label says there may be more frequent recurrences in people who already have atrial fibrillation. Meta analysis of randomised trials and regulator label 6 17 5 18
- Fish oil may prolong bleeding time; tell your doctor if you take blood thinners. The prescription omega-3 label says omega-3 acids may prolong bleeding time (within normal limits and without clinically significant bleeding in trials) and that people taking anticoagulants or anti-platelet drugs should be monitored. VITAL found no excess bleeding. A 2024 review found no overall difference in bleeding but said prescription EPA ethyl ester had a higher bleeding risk. Tell your doctor or pharmacist, and before any operation. Regulator label, randomised trial and meta analysis 18 9 17
- Fish or shellfish allergy. The prescription label says it is not known whether people allergic to fish or shellfish are at higher risk of a reaction to omega-3 from fish oil, and advises caution. Reports after approval include allergic reactions (anaphylaxis, hives). Ask a doctor first if you have a fish or shellfish allergy. Regulator label 18
- Fish liver oils (cod liver oil) are not the same as fish oil. NCCIH says fish liver oils contain vitamins A and D as well as EPA and DHA, and that vitamins A and D can be harmful in excessive amounts. The NHS says to avoid fish liver oil supplements in pregnancy, because too much vitamin A can harm an unborn baby, and not to exceed 1.5 mg of vitamin A a day from food and supplements together. Ordinary fish oil capsules are made from the oil of the fish body, not the liver, but check the label. Health agency guidance 19 20
Side effects 4
| Effect | How often | Severity and recovery | Evidence |
|---|---|---|---|
| Fishy taste, bad breath, bad-smelling sweat, heartburn, nausea, diarrhoea and headache In a depression review, side effects with omega-3 were similar to placebo but the numbers were imprecise. | The prescription label lists belching (eructation), indigestion and taste changes as the most common side effects (above 3% and more than placebo). In STRENGTH, stomach side effects were 24.7% with a prescription EPA plus DHA product versus 14.7% with corn oil. | Usually mild Not stated in the sources read. | Health agency, regulator label and randomised trial 19 18 11 |
| Atrial fibrillation (irregular heartbeat) Trials were designed to look at heart outcomes, so rhythm was reported in different ways. | HR 1.25 across 7 large trials; larger in trials testing larger daily amounts (details in studies table). | Can be serious; needs medical care Not stated in the sources read. | Meta analysis of randomised trials 6 17 |
| Longer bleeding time; higher bleeding risk with prescription EPA ethyl ester | Label: bleeding time stayed within normal limits in trials. Prescription EPA ethyl ester had a higher bleeding risk in a 2024 review; VITAL (capsules) showed no excess bleeding. | Usually within normal limits, but a concern with blood thinners Not stated. | Regulator label and meta analysis 18 17 9 |
| Raised liver blood tests (ALT) and, with EPA plus DHA prescription products, raised LDL cholesterol | Label: ALT rose in some patients; it advises periodic ALT and AST checks in people with liver impairment, and periodic LDL monitoring. | Lab changes; not described as liver damage Not stated. | Regulator label (prescription product) 18 16 |
Liver
The prescription omega-3 label says ALT (a liver blood test) rose in some patients without a matching rise in AST, and advises periodic ALT and AST tests in people with liver impairment. No cases of liver injury from ordinary fish oil were found in the sources read. The liver-safety reference LiverTox was not opened for this page. 18
How often. No frequency for ordinary fish oil was found.
Monitoring. The label (prescription product) advises periodic ALT and AST checks in liver impairment.
This is a safety connection. It is not evidence that Fish oil supports liver health.
Medicines and supplements 5
| With | Why it matters | Importance | Evidence | What to do |
|---|---|---|---|---|
| Anticoagulants and anti-platelet drugs (for example warfarin-type blood thinners, aspirin-type drugs) prescription | Omega-3 acids may prolong bleeding time (stated on the label). | The label says prolongation stayed within normal limits and caused no clinically significant bleeding in trials, but that trials of omega-3 with anticoagulants have not been done thoroughly, and advises periodic monitoring. | Regulator label Low certainty 18 | Tell your doctor or pharmacist before taking fish oil with a blood thinner. |
| Statins (simvastatin, atorvastatin, rosuvastatin) prescription | No change in how the statins were absorbed or cleared. | The label reports 14-day studies in healthy adults where omega-3 ethyl esters did not change levels of these three statins. Many people in the large trials took statins with omega-3. | Regulator label (healthy volunteer studies) Moderate certainty 18 | No change needed was reported for these three statins; still tell your pharmacist about all supplements. |
| Warfarin (effect on INR blood-clotting tests) prescription | Not established. | The label names anticoagulants as a group. Studies of warfarin dose or INR changes with fish oil were not found in the sources read, so a specific effect is not confirmed. | Gap Not enough evidence | Ask your clinic whether extra INR checks are wanted. |
| Cod liver oil and other products with vitamin A or vitamin D supplement | Fish liver oils add vitamins A and D, which build up if too much is taken. | NCCIH says vitamins A and D can be harmful in excessive amounts. The NHS sets a 1.5 mg a day limit for vitamin A from food and supplements combined. | Health agency guidance Moderate certainty 19 20 | Count all products that contain vitamin A or D; ask a pharmacist. |
| Meals that contain fat food | A 2013 review says taking omega-3 capsules with food, and with fat in the food, changes how well EPA and DHA are absorbed. | This affects how much EPA and DHA gets into the blood, not safety. The review calls for more systematic study. | Narrative review Low certainty 14 | Follow the label or ask a pharmacist. |
Who should check first 5
| Situation | Advice | Evidence |
|---|---|---|
| Pregnancy and breastfeeding | A 2018 Cochrane review of omega-3 in pregnancy found fewer preterm births but more births after 42 weeks (see Benefits). The NHS says to avoid fish liver oil supplements, such as cod liver oil, in pregnancy because of vitamin A. The prescription label says data are insufficient to identify a risk of birth defects and that EPA and DHA appear in breast milk. Ask a doctor or midwife before using any supplement. | Systematic review, health agency guidance and regulator label 10 20 18 |
| Children and teenagers | The prescription label says safety and effectiveness in children have not been established. A 2023 Cochrane review found side effects no different from placebo in children with ADHD, but no benefit for symptoms. The NHS gives limits on oily fish for children (boys up to 4 portions a week, girls no more than 2). Ask a doctor or pharmacist before giving a child a supplement. | Regulator label, systematic review and guidance 18 7 20 |
| People with a fish or shellfish allergy | Use only with medical advice (see Safety highlights). | Regulator label 18 |
| People with atrial fibrillation or other heart rhythm problems | Fish oil has been linked to more atrial fibrillation in trials, and the label links omega-3 to more frequent recurrences in people who already have it. Ask your cardiologist before using fish oil. | Meta analysis and regulator label 6 18 |
| People with liver disease, bleeding problems, or about to have surgery | The label advises periodic liver tests in liver impairment and monitoring with drugs that affect clotting. No source read gave specific surgery advice. Ask your doctor. | Regulator label 18 |
Overdose, product quality and regulators
Summary. Fish oil is generally tolerated at the amounts studied, with mostly mild stomach and taste side effects. The main concerns are atrial fibrillation at larger amounts, effects on bleeding time, and, for fish liver oils, too much vitamin A or D.
Animal. The prescription label reports rat and rabbit studies that found no harm to the fetus at the amounts tested; this is regulator information about a medicine.
High dose or long term signals. Atrial fibrillation risk rose with larger daily amounts in trials (HR 1.49 in trials testing larger amounts versus 1.12 in trials testing smaller amounts; the cut-off is in the studies table). Stomach side effects were common with a large prescription amount.
Overdose response. Not described in the sources read. If someone has taken a lot of a fish liver oil product, call poison control.
Genotoxicity. Not researched.
Three product-testing studies gave different answers. Quality seems to depend on the market and the product, so a general verdict cannot be given.
Label accuracy and oxidation: New Zealand 2015. Only 3 of 32 products had as much EPA and DHA as labelled, and most had gone off beyond recommended limits (oxidation markers). 3
Label accuracy and oxidation: Australia and New Zealand 2016. All 10 products tested met their label claims and the peroxide limit. The abstract says it was written to assist industry. 12
Label accuracy and oxidation: France 2022. Only 2.5% of 20 supplements fell short of label claims and all met industry oxidation limits. 13
Pollutants. The NHS says oily fish tend to have more pollutants than other seafood, hence portion limits for some groups. Whether fish oil capsules carry pollutants or heavy metals was not researched for this page. 20
| Body | Action | Date |
|---|---|---|
| NHS (England) (United Kingdom) | Says to eat at least 2 portions of fish a week including 1 of oily fish (a portion is about 140 g cooked); to avoid fish liver oil supplements in pregnancy; and not to have more than 1.5 mg of vitamin A a day from food and supplements together. Oily fish limits apply to girls, women who may become pregnant, and pregnant or breastfeeding women. source | 2026-06-26 |
| NCCIH (US National Institutes of Health) (United States) | States that side effects of omega-3 supplements are usually mild (taste, bad breath, smelly sweat, headache, heartburn, nausea, diarrhoea), that US dietary guidelines advise 8 ounces or more of seafood a week for adults, and that fish liver oils carry vitamins A and D that can be harmful in excess. source | 2024-11 |
| US FDA (prescribing information on DailyMed) (United States) | For a prescription omega-3 ethyl ester medicine: indicated as an add-on to diet for adults with very high triglycerides (500 mg per dL or more); cautions on fish and shellfish allergy, recurrent atrial fibrillation or flutter, bleeding time with anticoagulants, liver tests and LDL cholesterol; safety in children not established. This is not a statement about over-the-counter fish oil. source | 2026-05 |
When to get medical help
- A fast, pounding or irregular heartbeat, chest pain, fainting or breathlessness: get medical help straight away.
- Bleeding that will not stop, blood in vomit, urine or stools, black stools, or a large unexplained bruise (especially if you take a blood thinner): see a doctor.
- Swelling of the lips, face or throat, hives or trouble breathing after taking fish oil (possible allergy): call emergency services.
- Severe or lasting stomach pain, vomiting or diarrhoea: stop and see a doctor.
- Someone has swallowed a large amount of a product that contains vitamin A or D (such as cod liver oil): call poison control or emergency services.
Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.
General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.
Frequently asked questions
What is fish oil?
Is fish oil the same as cod liver oil, krill oil or flaxseed oil?
No. NCCIH says cod liver oil is a fish liver oil with added vitamins A and D, krill oil carries omega-3 as phospholipids, algal oil is a vegetarian source of DHA, and flaxseed oil gives the plant omega-3 ALA instead of EPA and DHA.
Does fish oil lower triglycerides?
Does fish oil prevent heart attacks?
Is eating fish better than taking fish oil?
Does fish oil help depression?
Does fish oil help children with ADHD?
No benefit was found. A 2023 Cochrane review rated as high certainty that omega-3 and similar supplements do not improve parent-rated ADHD symptoms.
Is fish oil safe in pregnancy?
Can fish oil cause an irregular heartbeat?
Does fish oil interact with blood thinners?
Does fish oil help the eyes?
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Editorial transparency
- Written by
- AlternativeMed editorial team. Research compiled with AI assistance, then checked against the sources listed.
- Medical review
- None. This page has not been reviewed by a physician or pharmacist.
- First published
- 2026-10-26
- Last substantive update
- 2026-10-26
- How we research
- We started from our existing fish oil summary, then read the NCCIH omega-3 page, the NHS fish page and a US prescription omega-3 label, and re-read PubMed abstracts for reviews and trials. Only abstracts were read for studies. The NIH Office of Dietary Supplements page and the EFSA opinion were blocked and are marked unread.
- How we rate evidence
- See "How we rate evidence" in the Evidence tab.
- Independence
- No product is promoted on this page. No affiliate links are shown. Two prescription-drug trials are flagged for drug-company links.
Sources 20
Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.
- Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ et al.. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease.. Cochrane Database Syst Rev. 2020. PMID 32114706. DOI 10.1002/14651858.CD003177.pub5. (abstract)
- Age-Related Eye Disease Study 2 Research Group. Lutein + zeaxanthin and omega-3 fatty acids for age-related macular degeneration: the Age-Related Eye Disease Study 2 (AREDS2) randomized clinical trial.. JAMA. 2013. PMID 23644932. DOI 10.1001/jama.2013.4997. (abstract)
- Albert BB, Derraik JG, Cameron-Smith D, Hofman PL, Tumanov S, Villas-Boas SG et al.. Fish oil supplements in New Zealand are highly oxidised and do not meet label content of n-3 PUFA.. Sci Rep. 2015. PMID 25604397. DOI 10.1038/srep07928. (abstract)
- Appleton KM, Voyias PD, Sallis HM, Dawson S, Ness AR, Churchill R et al.. Omega-3 fatty acids for depression in adults.. Cochrane Database Syst Rev. 2021. PMID 34817851. DOI 10.1002/14651858.CD004692.pub5. (abstract)
- Bhatt DL, Steg PG, Miller M, Brinton EA, Jacobson TA, Ketchum SB et al.. Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia.. N Engl J Med. 2019. PMID 30415628. DOI 10.1056/NEJMoa1812792. (abstract)
- Gencer B, Djousse L, Al-Ramady OT, Cook NR, Manson JE, Albert CM. Effect of Long-Term Marine ɷ-3 Fatty Acids Supplementation on the Risk of Atrial Fibrillation in Randomized Controlled Trials of Cardiovascular Outcomes: A Systematic Review and Meta-Analysis.. Circulation. 2021. PMID 34612056. DOI 10.1161/CIRCULATIONAHA.121.055654. (abstract)
- Gillies D, Leach MJ, Perez Algorta G. Polyunsaturated fatty acids (PUFA) for attention deficit hyperactivity disorder (ADHD) in children and adolescents.. Cochrane Database Syst Rev. 2023. PMID 37058600. DOI 10.1002/14651858.CD007986.pub3. (abstract)
- Kosti RI, Kasdagli MI, Kyrozis A, Orsini N, Lagiou P, Taiganidou F et al.. Fish intake, n-3 fatty acid body status, and risk of cognitive decline: a systematic review and a dose-response meta-analysis of observational and experimental studies.. Nutr Rev. 2022. PMID 34605891. DOI 10.1093/nutrit/nuab078. (abstract)
- Manson JE, Cook NR, Lee IM, Christen W, Bassuk SS, Mora S et al.. Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer.. N Engl J Med. 2019. PMID 30415637. DOI 10.1056/NEJMoa1811403. (abstract)
- Middleton P, Gomersall JC, Gould JF, Shepherd E, Olsen SF, Makrides M. Omega-3 fatty acid addition during pregnancy.. Cochrane Database Syst Rev. 2018. PMID 30480773. DOI 10.1002/14651858.CD003402.pub3. (abstract)
- Nicholls SJ, Lincoff AM, Garcia M, Bash D, Ballantyne CM, Barter PJ et al.. Effect of High-Dose Omega-3 Fatty Acids vs Corn Oil on Major Adverse Cardiovascular Events in Patients at High Cardiovascular Risk: The STRENGTH Randomized Clinical Trial.. JAMA. 2020. PMID 33190147. DOI 10.1001/jama.2020.22258. (abstract)
- Nichols PD, Dogan L, Sinclair A.. Australian and New Zealand Fish Oil Products in 2016 Meet Label Omega-3 Claims and Are Not Oxidized.. Nutrients. 2016. PMID 27827947. DOI 10.3390/nu8110703. (abstract)
- Pasini F, Gomez-Caravaca AM, Blasco T, Cvejic J, Caboni MF, Verardo V.. Assessment of Lipid Quality in Commercial Omega-3 Supplements Sold in the French Market.. Biomolecules. 2022. PMID 36291569. DOI 10.3390/biom12101361. (abstract)
- Schuchardt JP, Hahn A.. Bioavailability of long-chain omega-3 fatty acids.. Prostaglandins Leukot Essent Fatty Acids. 2013. PMID 23676322. DOI 10.1016/j.plefa.2013.03.010. (abstract)
- Sigaux J, Mathieu S, Nguyen Y, Sanchez P, Letarouilly JG, Soubrier M et al.. Impact of type and dose of oral polyunsaturated fatty acid supplementation on disease activity in inflammatory rheumatic diseases: a systematic literature review and meta-analysis.. Arthritis Res Ther. 2022. PMID 35526074. DOI 10.1186/s13075-022-02781-2. (abstract)
- Skulas-Ray AC, Wilson PWF, Harris WS, Brinton EA, Kris-Etherton PM, Richter CK et al.. Omega-3 Fatty Acids for the Management of Hypertriglyceridemia: A Science Advisory From the American Heart Association.. Circulation. 2019. PMID 31422671. DOI 10.1161/CIR.0000000000000709. (abstract)
- Yan J, Liu M, Yang D, Zhang Y, An F. Efficacy and Safety of Omega-3 Fatty Acids in the Prevention of Cardiovascular Disease: A Systematic Review and Meta-analysis.. Cardiovasc Drugs Ther. 2024. PMID 36103100. DOI 10.1007/s10557-022-07379-z. (abstract)
- . DailyMed: prescribing information, omega-3-acid ethyl esters capsules (Strides Pharma; revised 05/2026). . . (full-text)
- . NCCIH: Omega-3 Supplements: What You Need To Know (last updated November 2024). . . (full-text)
- . NHS: Fish and shellfish (page last reviewed 26 June 2026). . . (full-text)
Where to buy
Check the label first. Whatever you buy, look for these:
- EPA and DHA amounts per serving, not just the total fish oil
- Whether it is triglyceride form or ethyl ester form
- A third-party testing mark (IFOS, USP or NSF) for purity
- Fish or shellfish allergy information, and how many softgels make a serving
Talk to a pharmacist or doctor before you start any supplement, especially if you take medicines. See the Safety tab for interactions.
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