Fish Oil: What It Is, Evidence, Forms and Safety
Fish oil explained in plain language: what it contains, what large reviews and trials found, how EPA and DHA differ from the oil weight, forms, side effects, medicine cautions and safety.
Content last updated . This page has not been medically reviewed.
What is Fish oil good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Supplies EPA and DHA
Established roleFish oil is a source of the long-chain omega-3 fats EPA and DHA.
Supplements: Supplies the fats; whether extra helps depends on the use and is often unproven in well-nourished people.
Lowering blood triglycerides
Clinically supportedEPA and DHA lower blood triglycerides (a blood fat) by about 15% on average. Very high levels are treated with prescription products under medical care.
Supplements: Established effect on a blood measure; it is not by itself a proven health outcome.
Heart and circulation
Preliminary or mixedLarge reviews found little or no effect on overall death or heart events, and a possible small effect on coronary events.
Supplements: Mixed: not a proven way to prevent heart attacks or strokes in most adults.
Brain and nervous system development
Established roleThe NHS notes omega-3 supports a baby's nervous system development in pregnancy and breastfeeding.
Supplements: Normal role; extra fish oil in adults has early, mixed evidence for memory or decline.
Pregnancy and early development
Preliminary or mixedReviews of omega-3 in pregnancy gave mixed results for preterm birth and birth weight and limited evidence for child thinking skills.
Supplements: Mixed. Fish liver oils such as cod liver oil should be avoided in pregnancy because of vitamin A (NHS); that is a different product.
Mood and depression
Preliminary or mixedA 2021 review found any effect on depression may be too small to matter.
Supplements: Uncertain, low-quality evidence.
Joint pain in rheumatoid arthritis
Preliminary or mixedReviews suggest omega-3-rich foods may reduce joint pain and swelling, with low-quality evidence.
Supplements: Low-quality, mixed; do not change prescribed medicines.
Eye health (dry eye, macular degeneration)
Preliminary or mixedThe DREAM trial in 535 people found fish oil no better than placebo for dry eye, and AREDS2 found no extra benefit for macular degeneration.
Supplements: No benefit shown in the large trials read.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Health goals (4)
- Heart HealthPreliminary or mixed
Large reviews of fish oil supplements in adults mostly found little or no effect on death or overall heart events, with a possible small effect on coronary events. Results are mixed.
- Brain HealthPreliminary or mixed
A 2022 review suggested omega-3s may protect against cognitive decline in healthy people but had no effect in people already diagnosed with Alzheimer's. Evidence is early and mixed.
- Joint SupportPreliminary or mixed
A 2022 review of 30 studies in rheumatoid arthritis suggested omega-3-rich foods may improve pain and joint swelling; another 2021 review found lower pain but rated the evidence low.
- Mood BalancePreliminary or mixed
A 2021 review of 35 studies found any effect on depression may be too small to matter, with low-quality evidence. Some reviews suggest EPA may work better, and perhaps alongside antidepressants.
Body systems (6)
- Cardiovascular SystemPreliminary or mixed
Large reviews of fish oil supplements in adults mostly found little or no effect on death or overall heart events, with a possible small effect on coronary events. Results are mixed. It does lower blood triglycerides by about 15% on average.
- Heart & CirculationPreliminary or mixed
Large reviews of fish oil supplements in adults mostly found little or no effect on death or overall heart events, with a possible small effect on coronary events. Results are mixed.
- Nervous SystemEstablished role
The NHS notes omega-3 supports a baby's nervous system development in pregnancy and breastfeeding. This is a normal role of omega-3; it does not show extra supplements help people who already eat enough.
- Bones, Joints & MusclesPreliminary or mixed
A 2022 review of 30 studies in rheumatoid arthritis suggested omega-3-rich foods may improve pain and joint swelling; another 2021 review found lower pain but rated the evidence low.
- Brain & FocusPreliminary or mixed
Some reviews suggest a possible protective effect on cognitive decline in healthy people, but evidence is early and mixed; a 2023 review found no evidence fish oil-type supplements improve ADHD symptoms.
- Stress & MoodPreliminary or mixed
Evidence for depression is uncertain; a 2021 review found any effect may be too small to matter.
Body parts (4)
- HeartDocumented risk
A 2021 analysis of 7 large trials found more atrial fibrillation (an irregular heartbeat) with marine omega-3 supplements, with a higher signal in trials using more than 1 g a day. People with a heart rhythm condition should ask their clinician.
- Nervous SystemEstablished role
The NHS notes omega-3 supports a baby's nervous system development. This is a normal role of omega-3 and not proof that supplements add benefit.
- BrainPreliminary or mixed
The brain is rich in DHA and the NHS notes omega-3 supports a baby's nervous system development. Extra fish oil in adults has only early, mixed evidence for cognition.
- JointsPreliminary or mixed
A 2022 review of 30 studies in rheumatoid arthritis suggested omega-3-rich foods may improve pain and joint swelling; another 2021 review found lower pain but rated the evidence low.
Functional actions (4)
- Cardiovascular SupportPreliminary or mixed
Large reviews of fish oil supplements in adults mostly found little or no effect on death or overall heart events, with a possible small effect on coronary events. Results are mixed.
- Joint SupportPreliminary or mixed
A 2022 review of 30 studies in rheumatoid arthritis suggested omega-3-rich foods may improve pain and joint swelling; another 2021 review found lower pain but rated the evidence low.
- Mood SupportPreliminary or mixed
A 2021 review found any mood effect may be too small to be meaningful, with low-quality evidence.
- Nervous System SupportEstablished role
Omega-3 supports a baby's nervous system development (NHS). Supplements are not shown to add benefit beyond adequate intake.
Root causes (1)
- Medication Side EffectsDocumented risk
Prescription omega-3 labels say omega-3 acids may prolong bleeding time and people on anticoagulant or antiplatelet drugs should be monitored. Ask a pharmacist before combining, and do not stop prescribed medicine on your own.
Biomarkers (1)
- TriglyceridesClinically supported
EPA and DHA from supplements lowered blood triglycerides by about 15% on average in a 2020 review. Prescription omega-3 products are approved only for very high triglycerides under medical care.
Conditions & symptoms (8)
- HypertriglyceridemiaClinically supported
Supplements lowered triglycerides by about 15% on average; prescription omega-3 ethyl esters are approved as an add-on to diet for severe hypertriglyceridemia (500 mg/dL or more) under medical care. The effect on heart outcomes was not determined.
- Allergy To FishDocumented risk
Prescription omega-3 labels advise caution in people with known fish or shellfish hypersensitivity.
- Atrial FibrillationDocumented risk
Trials found more atrial fibrillation with marine omega-3 supplements, higher above 1 g a day; prescription labels mention possible more frequent recurrences in people with existing AF.
- Coronary Heart DiseasePreliminary or mixed
Reviews show a possible slight reduction in coronary events (low certainty) but little or no effect on overall death or heart events.
- Prolonged Bleeding TimeDocumented risk
Prescription omega-3 labels say omega-3 acids may prolong bleeding time, within normal limits in trials; monitor people on anticoagulant or antiplatelet drugs.
- Depressive DisorderPreliminary or mixed
A 2021 review found any effect may be too small to matter, with low-quality evidence.
- Premature BirthPreliminary or mixed
A 2018 review found fewer preterm births with omega-3 in pregnancy, while a 2016 AHRQ review found no effect on premature birth: mixed.
- Rheumatoid ArthritisPreliminary or mixed
Reviews suggest less pain and joint swelling with omega-3-rich foods; evidence is low quality.
Documented risks and interactions (3)
- Irregular heartbeat risk (atrial fibrillation). Large trials linked marine omega-3 supplements to more atrial fibrillation, more at higher intakes.
- Bleeding time and blood thinners. Prescription omega-3 labels say omega-3 acids may prolong bleeding time and that people on anticoagulants should be monitored.
- Fish and shellfish allergy. Prescription omega-3 labels advise caution in people with known fish or shellfish hypersensitivity.
Quick safety points first
- Fish or shellfish allergy. The prescription omega-3 labels say people with a known fish or shellfish allergy should be told about possible allergic reactions and should stop the product and seek medical attention if a reaction occurs. [1] Over-the-counter fish oil has no such label text in the sources we read, so ask an allergist or pharmacist first. In a US emergency, call 911.
- Blood thinners and surgery. Prescription omega-3 labels say omega-3 acids may prolong bleeding time and that people on anticoagulants or antiplatelet drugs should be monitored. [2] NCCIH advises telling your providers about every supplement well before an operation. [3] Never stop a prescribed medicine on your own; ask the prescriber or a pharmacist; see medication interactions.
- Fish liver oil is a different product. The NHS says to avoid fish liver oil supplements in pregnancy because they are high in vitamin A. [4] See cod liver oil.
What fish oil is
Fish oil supplements contain the long-chain omega-3 fats EPA and DHA. [5] In the US they are sold as dietary supplements, and the FDA says the companies, not the agency, are responsible for evaluating safety and labeling before marketing. [6] That is different from prescription omega-3 medicines, which are approved drugs for specific conditions; see prescription omega-3 vs supplements. Fish as a food is covered in oily fish.Food first?
NCCIH says that for some health conditions the evidence for benefit from seafood is stronger than for omega-3 supplements, partly because seafood has other nutrients and fish eaters tend to have healthier lifestyles. [5] The NHS says a balanced diet should include at least 2 portions of fish a week, including 1 of oily fish. [4] See omega-3 supplements vs eating fish.What the evidence shows
Evidence labels used here: evidence in adequately nourished people, mixed, established effect on a blood measure, insufficient evidence. Prescription EPA-only and mixed products are different interventions.| Question | What the source found | Label |
|---|---|---|
| Death and heart events | Cochrane review (2020), 86 trials, 162,796 adults, 12 to 88 months: little or no effect on all-cause death (risk ratio 0.97) or cardiovascular events (0.96); slightly fewer coronary heart disease events (0.91, low certainty). [7] | Evidence in adequately nourished people: mostly no clear benefit |
| General population | VITAL trial, 25,871 adults, 1 g a day of marine omega-3s, median 5.3 years, placebo-controlled: no significant drop in major cardiovascular events (hazard ratio 0.92, 95% CI 0.80 to 1.06) or cancer. Heart attack hazard ratio 0.72 was a secondary result. [8] | Mixed |
| Triglycerides (a blood measure) | EPA and DHA lowered triglycerides by about 15% in a dose-dependent way (high certainty). [7] | Established effect on this blood measure; not itself a health outcome |
| Dry eye | DREAM trial, 535 adults with moderate-to-severe dry eye, 12 months: supplements were no more helpful than placebo. [5] | No benefit shown |
| Depression, ADHD | 2021 review of 35 studies on depression: if there is an effect it may be too small to be meaningful; 2023 review on ADHD in children: no evidence symptoms improve. [5] | Low or insufficient |
For more by condition, see omega-3 evidence by use and fish oil and heart attacks and strokes.
Amounts: study and official amounts, not advice
Trials used very different amounts. VITAL used 1 g a day of marine omega-3s. [8] The Cochrane review included trials from 0.5 g to more than 5 g a day of long-chain omega-3, and overall effects on heart outcomes did not differ by dose (the triglyceride effect did). [7] EFSA (EU, 2012) concluded that supplemental EPA plus DHA up to 5 g a day does not raise safety concerns for adults; it also said the data were not enough to set a tolerable upper intake level. [9] A recommended intake of EPA plus DHA from the NIH Office of Dietary Supplements could not be verified, because that site blocked our download. A clinician or pharmacist decides what is right for a person.EPA and DHA versus "fish oil 1000 mg"
The front of a bottle may say "fish oil 1,000 mg", but the omega-3 is only part of that weight. As a made-up example, a capsule could hold 1,000 mg of oil and a smaller amount of EPA plus DHA; the Supplement Facts line for EPA and DHA is the number to read. A 2022 study of top-selling fish oil products found that fatty acid content matched the label in all capsules but fell short of the label in about one third of the liquid (syrup) products tested. [10] See how to read a fish oil label.Forms
Omega-3 oils come as ethyl esters, free fatty acids, triglycerides and phospholipids. A 2014 review found apparent absorption seemed lowest for the ethyl ester form and highest for free fatty acids, but the studies were too different to draw firm conclusions, and no conclusion could be made for triglyceride versus phospholipid in humans. [11] A four-week trial in 66 healthy adults with matched EPA plus DHA (1.3 g a day) found no significant difference in plasma levels between ethyl ester fish oil, triglyceride fish oil and krill oil. [12] Blood levels are a biomarker, not a health outcome.Side effects and other cautions
- Common effects are usually mild: unpleasant taste, bad breath, bad-smelling sweat, headache, heartburn, nausea and diarrhea. [5]
- Atrial fibrillation. A 2021 meta-analysis of 7 trials (81,210 adults) found marine omega-3 supplements linked to more atrial fibrillation (hazard ratio 1.25), higher in trials above 1 g a day (1.49). [13] People with a heart rhythm condition should talk with their clinician. See fish oil and atrial fibrillation.
- Quality. A study of Chinese-market products found 65.2% of capsules met a national oxidation standard and EPA content matched the label in 64% of capsules. [14] Results differ by country; see quality testing and certifications.
- Pregnancy, children, kidney or liver conditions. We did not find fish-oil-specific advice for these groups in the sources we read, so ask a clinician. See pregnancy and breastfeeding safety and omega-3 cautions.
Related
Krill oil, algal oil, fish oil vs krill oil, fish oil vs algal oil, omega-3 safety and interactions.Frequently asked questions
Does fish oil prevent heart attacks?
Reviews are mixed. Cochrane found little or no effect on overall death and cardiovascular events and a possible slight effect on coronary events (low certainty). [7] VITAL, in people without a prior event, found no significant drop in its main combined heart outcome. [8]
Does fish oil lower triglycerides?
On average, about 15% in a Cochrane review, in a dose-dependent way. [7] Very high triglycerides are managed with prescription products under medical care. [5]
Is fish oil safe every day?
Side effects are usually mild. [5] Higher amounts are linked in trials with more atrial fibrillation, [13] and bleeding cautions apply with some medicines. [2] Check with a pharmacist.
Is fish oil better than eating fish?
NCCIH says that for some conditions the evidence for seafood is stronger than for supplements. [5]
Is fish oil the same as cod liver oil?
No. Cod liver oil is a fish liver oil that also supplies vitamins A and D in amounts that vary by product. [5]
References
- FDA-approved prescribing information, Vascepa (icosapent ethyl), DailyMed. Read 2026-10-22.
- FDA-approved prescribing information, omega-3-acid ethyl esters capsules (generic prescription product), DailyMed, revised 5/2026. Read 2026-10-22.
- NCCIH, Using Dietary Supplements Wisely. Read 2026-10-22.
- NHS, Fish and shellfish. Read 2026-10-22.
- NCCIH, Omega-3 Supplements: What You Need To Know. Read 2026-10-22.
- FDA, Dietary Supplements. Read 2026-10-22.
- Abdelhamid AS et al., Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease, Cochrane Database Syst Rev 2020. Read 2026-10-22.
- Manson JE et al., Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer (VITAL), N Engl J Med 2019. Read 2026-10-22.
- EFSA, EFSA assesses safety of long-chain omega-3 fatty acids (2012 news story). Read 2026-10-22.
- Assessment of the safety of dietary fish oil supplements in terms of content and quality, 2022. Read 2026-10-22.
- Hawthorne/Ghasemifard et al., Omega-3 long chain fatty acid "bioavailability": a review of evidence and methodological considerations, Prog Lipid Res 2014. Read 2026-10-22.
- Schuchardt/Köhler et al., Similar EPA and DHA plasma levels achieved with fish oil or krill oil in a randomized double-blind four-week bioavailability study, 2015. Read 2026-10-22.
- Gencer B et al., Effect of Long-Term Marine n-3 Fatty Acids Supplementation on the Risk of Atrial Fibrillation in Randomized Controlled Trials of Cardiovascular Outcomes, Circulation 2021. Read 2026-10-22.
- Systematically Investigating the Qualities of Commercial Encapsulated and Industrial-Grade Bulk Fish Oils in the Chinese Market, 2025. Read 2026-10-22.