Vitamins & Supplements · Amino acid
Carnitine
L-carnitine · also called L-carnitine, acetyl-L-carnitine (ALC)
Carnitine is a vitamin-like compound the body makes to burn fat for energy. People who eat meat also get most of theirs from food, especially red meat. In trials, pills gave a small average fall in weight, and mixed results for the heart; evidence for nerve pain and memory is weak. Gut bacteria turn carnitine into TMAO, so people with heart disease or on thyroid medicine should ask a doctor 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 Carnitine
Carnitine is a vitamin-like compound that helps the body burn fat for energy. The body makes it, and meat is a rich source. Pills show small, mixed results for weight and heart measures, and the gut-bacteria (TMAO) question needs a doctor for people with heart disease.
What carnitine is
Carnitine is a vitamin-like compound made from the amino acids lysine and methionine. Its main job is to carry long-chain fats into the mitochondria, the cell's energy units, where they are burned. Inherited problems with carnitine can cause low blood sugar, weak heart muscle and liver disease.
Supplements come as L-carnitine, acetyl-L-carnitine and other forms. Acetyl-L-carnitine is a derived form that has been studied for nerve pain and brain conditions.
Food and the body's own supply
In people who eat meat, about 75% of carnitine comes from food and about 25% is made in the body (2019 review). Papers on carnitine describe red meat as an abundant source. Amounts per portion are not given here because the official NIH fact sheet could not be opened.
Food carnitine and supplement carnitine are not the same thing. Gut bacteria handle them differently depending on a person's usual diet.
What the research shows
The best-studied uses are body weight (small average fall), heart attack and heart failure (mixed, older evidence), nerve pain with acetyl-L-carnitine (very uncertain), and blood markers in type 2 diabetes (small). No clear benefit was found for dementia or for people on dialysis.
Most results are from supplements in people with a health condition, not from healthy people eating meat.
At a glance
Traditional uses history, not proof
- Made in the body and eaten in meat
- Sold as a fat-burning and sports supplement
Studied for research
- Role in the body and food sources, high certainty
- Inherited carnitine shortage, high certainty that it exists
- Body weight, low certainty
- Heart attack and heart failure, low certainty
- Type 2 diabetes and liver blood markers, low certainty
- Nerve pain (acetyl-L-carnitine), very low certainty
- Memory and dementia, insufficient evidence
Main compounds
- L-carnitine
- Acetyl-L-carnitine
- TMAO (gut-bacteria product)
Common forms
- Food (mostly meat)
- Capsules, tablets and powders of L-carnitine or acetyl-L-carnitine
Research links: 2020 meta-analysis: L-carnitine and weight (37 trials) · 2019 Cochrane review: acetyl-L-carnitine for diabetic nerve damage · 2013 review: L-carnitine after a heart attack · 2019 trial: gut bacteria, carnitine and TMAO · 2001 trial: L-carnitine and thyroid hormone · Research Library · Genes & Biomarkers Library
What it is and its history
- Accepted scientific name
- Carnitine (L-carnitine, 3-hydroxy-4-trimethylammoniobutanoate), a vitamin-like amino acid derivative
- Synonyms
- L-carnitine
- Common names
- Carnitine (English); L-carnitine (English); Acetyl-L-carnitine (ALC) (English (a derived form)); Carnitina (Spanish)
- Family or group
- Amino acid derivative made from lysine and methionine; vitamin-like but not a vitamin.
- Look-alikes and adulterants
- Name: Acetyl-L-carnitine; Note: A form derived from carnitine; studied for nerve pain and brain conditions. Results should not be moved between forms.; Name: Propionyl-L-carnitine and L-carnitine L-tartrate; Note: Other forms named in the exercise review. Not compared here.
- Sustainability and conservation
- Not assessed.
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 |
|---|---|---|---|---|
| L-carnitine | amino acid derivative | Not read from a source. | The form tested for body weight, heart conditions, diabetes markers, liver enzymes and sperm quality. 16 5 15 11 | Human data |
| Acetyl-L-carnitine (ALC) | carnitine derivative | Not read from a source. | Derived from carnitine; tested for nerve pain and dementia. 13 6 | Human data |
| Trimethylamine-N-oxide (TMAO) | gut-bacteria product | Not applicable | Made when gut bacteria and the liver process carnitine (and choline); linked to artery disease in mice and in observational human data. 8 9 | Mouse and human observational |
Mechanisms, receptors and pathways
| Target or pathway | Gene or receptor | What was found | Level |
|---|---|---|---|
| Fat transport into mitochondria (the carnitine shuttle) | CPT I, CACT and CPT II enzymes; OCTN2 (SLC22A5) transporter takes carnitine into cells | A 2019 review says carnitine moves long-chain fats across the mitochondrial membrane so they can be burned (beta-oxidation). 1 | Human data |
| The body's own carnitine making | TMLD, HTMLA, TMABADH and BBD enzymes | The body makes carnitine from lysine and methionine in four enzyme steps (2019 review). 1 | Human data |
| Gut-bacteria breakdown to TMA and TMAO | Gut bacteria; one species (Emergencia timonensis) turns gamma-butyrobetaine into TMA | Gut bacteria turn carnitine into gamma-butyrobetaine and then TMA; TMAO follows. The second gut step is switched on by an omnivorous diet and by regular carnitine (2019 trial). 9 8 | Human data |
| Thyroid hormone entry into cells | Not specified | The authors of the 2001 trial say carnitine blocks thyroid hormone from entering cell nuclei in some tissues. 3 | Human (as stated by the authors) |
Absorption, metabolism and elimination
- Absorption
- Not described in the abstracts read.
- Distribution
- The transporter OCTN2 takes carnitine into cells (review).
- Metabolism
- Gut bacteria convert carnitine to gamma-butyrobetaine and TMA (2019 trial).
- Elimination
- Kidney reabsorption helps keep carnitine levels steady (review).
- Bioavailability
- Not compared across forms in the sources read.
Isolated compounds versus whole extracts
Food carnitine (mostly from meat) and supplement carnitine are not the same thing, and diet changes what gut bacteria do: the 2019 tracer study found people who regularly eat meat make far more TMAO from the same dose than vegans or vegetarians. No trial comparing food and pill sources was read.
Nutritional composition
No food amounts per portion are given: the NIH Office of Dietary Supplements fact sheet was blocked, and no other source read gives per-portion figures. Two papers describe carnitine as abundant in red meat; a 2019 review says meat eaters get about 75% of their carnitine from food.
2 high certainty7 low certainty1 very low certainty2 not enough evidence
What was looked at
The 12 benefits and uses checked for Carnitine, each with how strong the evidence is. Tap one to open it.
- What carnitine does in the body and where it comes fromHigh certainty
- Body weight and body fatLow certainty
- Inherited carnitine shortageHigh certainty
- Painful nerve damage (acetyl-L-carnitine)Very low certainty
- After a heart attackLow certainty
- Chronic heart failureLow certainty
- Dementia and memory (acetyl-L-carnitine)Not enough evidence
- Male infertility (sperm quality)Low certainty
- Exercise performance and recoveryLow certainty
- Blood sugar and cholesterol in type 2 diabetesLow certainty
- Liver blood testsLow certainty
- People having long-term kidney dialysisNot enough evidence
Lab markers tracked in the studies
Body weight (kg)Fat mass (kg)Nerve pain scoreHeart ejection fractionHbA1cLDL cholesterolLiver enzymes ALT and ASTSperm motility and shapeQuality of life in dialysis (SF-36)
What is Carnitine good for?
The main studied uses and how strong the human evidence is for each. Most results are for pills taken by people with a health condition, not for healthy people.
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.
What carnitine does in the body and where it comes from
High certaintyCarnitine carries fats into the cell's energy units so they can be burned for energy. People who eat meat get about three quarters of their carnitine from food; the body makes the rest.
3 studiesCarnitine as a nutrient from food. Forms in supplements (L-carnitine,…
Studies, doses and limits
What the trials found
A 2019 review says that in people who eat meat about 75% of carnitine comes from the diet and about 25% is made in the body. Two research papers (2013 and 2019) describe carnitine as a nutrient abundant in red meat. Exact amounts per portion were not read, because the NIH fact sheet could not be opened.
Results
The normal job of carnitine is established. The sources read do not show that extra carnitine from pills gives more energy in people who already have normal levels.
Effect sizes as reported
No effect sizes apply: this is normal biology, not a trial result.
Why this rating
High that this is carnitine's role and that most comes from food in meat eaters (a review of the biology). Not a claim that pills add energy.
Form and dose studied
Carnitine as a nutrient from food. Forms in supplements (L-carnitine, acetyl-L-carnitine) are covered under the uses below.
Who was studied
Everyone.
Limits
The role is described in a narrative review, read from the abstract. Food amounts per portion were not read.
Why researchers looked
People ask whether they get enough carnitine, and whether extra helps energy.
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Established physiology
Carnitine shuttles long-chain fats across the membrane of the mitochondria (the cell's energy units), where they are burned. Three enzymes make up this shuttle. The body makes carnitine from lysine and methionine in four steps, and a transporter called OCTN2 takes it into cells.
A proposed mechanism does not show that the effect happens in people.
See the Safety tab for the gut-bacteria (TMAO) question.
Body weight and body fat
Low certaintyAcross dozens of trials, L-carnitine pills gave a small average fall in weight: about 1 kg more than placebo. The effect was seen mainly in people with overweight or obesity.
2 studiesL-carnitine taken by mouth in many forms and amounts across trials. A…
Studies, doses and limits
What the trials found
Two 2020 meta-analyses of randomised trials found the same thing. The first (37 trials, 2,292 people) found weight fell by 1.21 kg, BMI by 0.24 and fat mass by 2.08 kg compared with placebo; waist and body fat percent did not change. The second (43 trials) found a similar fall in weight (1.13 kg), BMI and fat mass, with no clear change in body fat percent or waist, and only in people with overweight or obesity. It also found no change in people having haemodialysis.
Results
A small average fall in body weight and fat mass in adults with overweight or obesity; no clear change in waist size or body fat percent. Trials differed a lot from one another.
Effect sizes as reported
Weight about -1.2 kg (95% CI -1.73 to -0.68) and -1.13 kg (-1.59 to -0.67); BMI -0.24 and -0.36 kg/m2; fat mass -2.08 and -1.16 kg.
Why this rating
Two consistent meta-analyses, but trials differed a lot (I2 up to 85% for BMI), the average change is small, and the abstracts do not give the size of each trial. The second review found the effect only alongside lifestyle changes.
Form and dose studied
L-carnitine taken by mouth in many forms and amounts across trials. Amounts are not compared here.
Who was studied
Adults, mostly with overweight or obesity.
Limits
Both reviews were read from abstracts only. The change of about 1 kg is small and may not matter to many people.
Why researchers looked
Carnitine moves fat into the cell's energy units, so it has long been sold for fat loss.
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Hypothesis
The idea is that more carnitine helps cells burn fat. This has not been shown to be the reason for the small average change.
A proposed mechanism does not show that the effect happens in people.
Taking pills for weight loss is a question for a doctor; see the Safety tab.
Inherited carnitine shortage
High certaintyRare inherited conditions stop the body from making, absorbing or using carnitine. They can cause low blood sugar, a weak heart and liver problems. These need medical care, not shop supplements.
2 studiesMedical treatment is directed by specialists; it is not covered here.
Studies, doses and limits
What the trials found
A 2019 review says inherited disorders of carnitine making, transport or use share low blood sugar without ketones, heart muscle disease and liver disease. MedlinePlus Genetics (page updated 2023-11-27) says primary carnitine deficiency affects about 1 in 100,000 newborns worldwide, can show up as brain dysfunction, a weak and enlarged heart, vomiting, muscle weakness and low blood sugar, can be set off by fasting or infections, and carries a risk of sudden death. Some people have no signs.
Results
A true carnitine shortage is rare and serious, and it is a medical diagnosis. It is a different situation from a healthy person asking whether pills help.
Effect sizes as reported
No effect sizes: these are descriptions of an inherited condition.
Why this rating
High that these inherited conditions exist and what they cause (a review and a national health database).
Form and dose studied
Medical treatment is directed by specialists; it is not covered here.
Who was studied
Newborns, children and adults with rare gene changes.
Limits
Read from a review abstract and a health-information page. This item does not describe treatment.
Why researchers looked
It shows what carnitine is needed for, and why a true shortage is serious.
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Established physiology
Gene changes in the carnitine transporter (SLC22A5, protein OCTN2) leave cells short of carnitine, so fats cannot enter the energy units. Fat then builds up in the liver, heart and muscle.
A proposed mechanism does not show that the effect happens in people.
Do not try to treat suspected carnitine deficiency yourself. Get urgent medical help for the signs listed on the Safety tab.
Painful nerve damage (acetyl-L-carnitine)
Very low certaintyAcetyl-L-carnitine, a form made from carnitine, has been tested for pain from nerve damage caused by diabetes or HIV medicines. One review says it helped; a stricter review says the evidence is very uncertain.
2 studiesAcetyl-L-carnitine by mouth, in amounts from 1,500 to 3,000 mg a day …
Studies, doses and limits
What the trials found
A 2019 review pooled 4 randomised trials (nerve damage from diabetes or HIV drugs) and found pain fell about 20% more than with placebo. Several of its authors report fees and grants from the maker. A 2019 Cochrane review of diabetic nerve damage (4 trials, 907 people) found pain on a 100 mm scale was 9 mm lower than with placebo (95% CI -16.76 to -1.57), but rated this very-low certainty and said it is very uncertain whether acetyl-L-carnitine reduces pain. Two of the four trials were funded by the manufacturer.
Results
Some pain reduction in some trials, but the strongest review calls the evidence very uncertain. Results for acetyl-L-carnitine should not be applied to plain L-carnitine.
Effect sizes as reported
Pooled pain reduction 20.2% (8.3% to 32.1%) in one review; mean difference -9.16 mm on a 100 mm scale (-16.76 to -1.57) in the Cochrane review.
Why this rating
The Cochrane reviewers rate the pain result very-low certainty (high risk of bias, inconsistent results, little data on function). Industry funding and ties in the trials and in one review.
Form and dose studied
Acetyl-L-carnitine by mouth, in amounts from 1,500 to 3,000 mg a day in the Cochrane trials. Not a dosing statement.
Who was studied
Adults with painful diabetic or HIV-drug nerve damage.
Limits
Few trials; no standard symptom scales; the benefit is small and uncertain.
Why researchers looked
Acetyl-L-carnitine is thought to protect nerves, so it has been tested in nerve pain (neuropathy).
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Hypothesis
Proposed: neuroprotective and nerve-growth effects (described in the Cochrane review). Not proven in people.
A proposed mechanism does not show that the effect happens in people.
Headache, facial tingling and stomach upset were reported; see the Safety tab.
After a heart attack
Low certaintyA 2013 review of 13 trials found fewer deaths, fewer abnormal heart rhythms and less angina with carnitine in people who had a heart attack. The death result was borderline and the authors call for new trials.
1 studiesL-carnitine; route (mouth or injection) and amounts are not given in …
Studies, doses and limits
What the trials found
A 2013 systematic review pooled 13 controlled trials (3,629 people after a heart attack). Carnitine was linked with fewer deaths (OR 0.73, 95% CI 0.54 to 0.99), fewer abnormal heart rhythms (RR 0.35) and less angina (RR 0.60). There was no clear fall in heart failure or in second heart attacks. The authors say bigger modern trials are needed.
Results
Fewer deaths, abnormal rhythms and angina, with a borderline death result. The authors say large trials in the modern era are still needed.
Effect sizes as reported
All-cause death OR 0.73 (0.54 to 0.99); arrhythmias RR 0.35 (0.21 to 0.58); angina RR 0.60 (0.50 to 0.72); heart failure RR 0.85 (0.67 to 1.09); second heart attack RR 0.78 (0.41 to 1.48).
Why this rating
Pooled trials with different designs, a borderline death result, and a review that itself calls for large modern trials. Read from the abstract only.
Form and dose studied
L-carnitine; route (mouth or injection) and amounts are not given in the abstract.
Who was studied
Adults after a heart attack.
Limits
Not a reason to take carnitine after a heart attack. Medicines and care for heart attacks are decided with a cardiologist.
Why researchers looked
The heart muscle burns fat for fuel, so carnitine has been tested in heart disease.
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Hypothesis
Not established in the abstract.
A proposed mechanism does not show that the effect happens in people.
The gut-bacteria (TMAO) question on the Safety tab is relevant for people with heart disease.
Chronic heart failure
Low certaintyA 2017 review of 17 trials found better heart pumping measures and lower BNP markers with L-carnitine added to usual care, but no clear difference in deaths or in the 6-minute walk.
1 studiesL-carnitine added to usual heart-failure care; amounts not given in t…
Studies, doses and limits
What the trials found
A 2017 meta-analysis of 17 randomised trials (1,625 people with chronic heart failure) found higher ejection fraction (+4.14 percentage points), more blood pumped per beat and per minute, and lower BNP and NT-proBNP markers. There were no significant differences in all-cause death, 6-minute walk or side effects.
Results
Better heart-function measures and lower blood markers, but no proof of longer life or better walking.
Effect sizes as reported
Ejection fraction +4.14 points; stroke volume +8.21 ml; NT-proBNP -510 pg/ml; death: no significant difference.
Why this rating
Improvements in measurements, not in survival or walking distance; the abstract does not describe trial quality or funding.
Form and dose studied
L-carnitine added to usual heart-failure care; amounts not given in the abstract.
Who was studied
Adults with chronic heart failure.
Limits
Read from the abstract only.
Why researchers looked
Carnitine has been tested as an add-on to usual heart-failure care.
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Hypothesis
Not established in the abstract.
A proposed mechanism does not show that the effect happens in people.
People with heart failure take several medicines; ask a doctor or pharmacist before adding any supplement.
Dementia and memory (acetyl-L-carnitine)
Not enough evidenceA Cochrane review of 11 trials in Alzheimer's disease found no benefit on thinking, severity or daily function. It is an older review (searched to 2003).
1 studiesAcetyl-L-carnitine by mouth; amounts not given in the abstract.
Studies, doses and limits
What the trials found
The Cochrane review (11 trials, all in Alzheimer's disease) found no benefit on cognition, severity of dementia or daily function. A doctor-rated overall impression was better at 12 and 24 weeks, but not at 52 weeks, and the authors say it may be chance. They found no evidence to recommend routine use. Adverse events did not differ between groups.
Results
No clear benefit for memory or dementia in Alzheimer's disease.
Effect sizes as reported
Overall impression OR 2.33 at 12 weeks (1.25 to 4.35) and OR 3.91 at 24 weeks (1.32 to 11.54); no benefit on cognition, severity or function.
Why this rating
Old review (2003), mostly completer analyses, many comparisons so a chance finding is possible; no newer review was read.
Form and dose studied
Acetyl-L-carnitine by mouth; amounts not given in the abstract.
Who was studied
People with Alzheimer's disease.
Limits
Does not cover healthy people or other kinds of dementia.
Why researchers looked
Acetyl-L-carnitine is marketed for the brain and memory.
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Hypothesis
Proposed: acts on brain chemicals and cell energy. Not shown to help in these trials.
A proposed mechanism does not show that the effect happens in people.
No difference in side effects was found in the review.
Male infertility (sperm quality)
Low certaintyIn men with infertility of unknown cause, L-carnitine or acetyl-L-carnitine improved sperm movement and shape in 8 trials, but did not raise sperm count or clearly raise pregnancy rates.
1 studiesL-carnitine or L-acetylcarnitine by mouth; amounts not given in the a…
Studies, doses and limits
What the trials found
A 2020 systematic review and meta-analysis of 8 randomised trials found carnitines significantly improved total sperm motility, progressive (forward) motility and normal shape, with no effect on sperm concentration. Five trials measured pregnancy; there was no demonstrable effect, though numbers were small.
Results
Better sperm movement and shape, but no proof of more pregnancies.
Effect sizes as reported
Not given as numbers in the abstract.
Why this rating
Eight small trials, pregnancy rates were not improved, and the review notes limited evidence.
Form and dose studied
L-carnitine or L-acetylcarnitine by mouth; amounts not given in the abstract.
Who was studied
Men with idiopathic (unexplained) infertility.
Limits
Sperm test changes are not the same as a baby. One author reports research funding from AstraZeneca.
Why researchers looked
The review notes that carnitine is normally abundant in the fluid of the male reproductive tract, and that it acts as an antioxidant in the body.
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Hypothesis
Proposed: carnitine acts as an antioxidant and lowers damage from reactive oxygen to sperm. Not proven.
A proposed mechanism does not show that the effect happens in people.
Couples trying to conceive should see a doctor about causes.
Exercise performance and recovery
Low certaintyEleven small trials gave mixed results. Some found better results in short, hard exercise; none found improvements in moderate exercise.
2 studiesL-carnitine, L-carnitine L-tartrate and glycine-propionyl-L-carnitine…
Studies, doses and limits
What the trials found
A 2021 systematic review of 11 trials found some improved results in high-intensity exercise (lower perceived effort, more power in short tests) but no improvement in moderate exercise. A 2020 review of healthy people taking carnitine for 12 weeks or more found muscle carnitine rose when it was taken with carbohydrate, muscle mass and effort tolerance improved in a group of very old women (centenarians), and muscle strength did not change in older women.
Results
Mixed and small. Benefits, where seen, were for hard exercise and specific groups.
Effect sizes as reported
No pooled numbers.
Why this rating
Small trials with different tests; a narrative review; few people in each.
Form and dose studied
L-carnitine, L-carnitine L-tartrate and glycine-propionyl-L-carnitine across trials; amounts are not compared here.
Who was studied
Healthy adults, athletes and a few older groups.
Limits
Results from one form do not carry to another; pooled analysis was not done.
Why researchers looked
Sold to athletes for fat burning and endurance.
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Hypothesis
Proposed: carnitine helps muscles burn fuel and recover. Muscle carnitine rose when taken with carbohydrate (2020 review).
A proposed mechanism does not show that the effect happens in people.
Fasting TMAO rose in the long trials; see Safety.
Blood sugar and cholesterol in type 2 diabetes
Low certaintyA 2024 meta-analysis of 21 trials found small average falls in HbA1c, fasting glucose and LDL cholesterol in people with type 2 diabetes. Results differed a lot between trials.
1 studiesL-carnitine by mouth; results reported per 1 g a day; not a dosing st…
Studies, doses and limits
What the trials found
A 2024 dose-response meta-analysis (21 randomised trials, 2,041 adults with type 2 diabetes) found that for every 1 g a day, HbA1c fell 0.16 points (95% CI -0.32 to -0.01), LDL cholesterol 0.11 mmol/L and fasting glucose 0.17 mmol/L. The authors graded HbA1c moderate, LDL high and BMI low, but say results must be read very cautiously because trials differed so much (I2 91% to 94%).
Results
Small lab-marker improvements in type 2 diabetes. It is not proof of fewer diabetes complications.
Effect sizes as reported
HbA1c MD -0.16% per 1 g/day (-0.32 to -0.01); LDL MD -0.11 mmol/L (-0.16 to -0.05); fasting glucose MD -0.17 mmol/L.
Why this rating
Blood markers only, with very large differences between trials; the authors' own GRADE ratings range from low to high by marker.
Form and dose studied
L-carnitine by mouth; results reported per 1 g a day; not a dosing statement.
Who was studied
Adults with type 2 diabetes.
Limits
No data on complications. Diabetes medicines are adjusted by a doctor.
Why researchers looked
Carnitine has been recommended to improve heart and metabolic health markers in people with diabetes.
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Hypothesis
Not established in the abstract.
A proposed mechanism does not show that the effect happens in people.
Ask a doctor or pharmacist before adding a supplement to diabetes treatment.
Liver blood tests
Low certaintyA 2020 meta-analysis of 18 trials found lower blood liver-enzyme levels (ALT, AST, GGT) with L-carnitine. These are blood tests, not proof of better liver health.
1 studiesL-carnitine by mouth; trials used 500 to 4,000 mg a day. Not a dosing…
Studies, doses and limits
What the trials found
A 2020 meta-analysis of 18 randomised trials (1,161 people) found ALT fell 8.65 IU/L, AST 8.52 IU/L and GGT 8.80 IU/L. The effect looked larger in people with liver disease, with longer treatment and at higher amounts. The authors rated the evidence moderate for ALT and AST and low for GGT.
Results
Lower liver enzymes in blood tests. Whether this means healthier livers was not shown.
Effect sizes as reported
ALT -8.65 IU/L (-13.40 to -3.90); AST -8.52 IU/L (-12.16 to -4.89); GGT -8.80 IU/L (-13.67 to -3.92).
Why this rating
Blood-marker result only (the reviewers' own marker grade was moderate); outcomes such as liver disease progression were not measured.
Form and dose studied
L-carnitine by mouth; trials used 500 to 4,000 mg a day. Not a dosing statement.
Who was studied
Adults, including people with liver disease.
Limits
Marker study only.
Why researchers looked
Carnitine has been proposed to lower liver enzymes, but earlier findings were mixed.
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Hypothesis
Not established in the abstract.
A proposed mechanism does not show that the effect happens in people.
Liver disease needs medical care; ask a doctor.
People having long-term kidney dialysis
Not enough evidenceA 2014 meta-analysis found no clear improvement from L-carnitine in quality of life, inflammation, anaemia or cholesterol in people on haemodialysis.
2 studiesL-carnitine versus placebo; amounts not given in the abstract.
Studies, doses and limits
What the trials found
The 2014 meta-analysis found no significant change in SF-36 quality of life (SMD 0.76, 95% CI -0.13 to 1.65), CRP, albumin, haemoglobin, cholesterol, triglycerides or parathyroid hormone. The authors say high-quality trials with hard endpoints are needed. A 2020 weight review also found no change in body measurements in people having haemodialysis.
Results
No clear benefit found in the trials pooled. Not enough evidence to say.
Effect sizes as reported
No significant pooled change in the markers measured.
Why this rating
Small trials and no hard outcomes such as hospital stays or death.
Form and dose studied
L-carnitine versus placebo; amounts not given in the abstract.
Who was studied
Adults on long-term haemodialysis.
Limits
Dialysis care is specialist care.
Why researchers looked
The meta-analysis says carnitine has been used as an add-on treatment in people on haemodialysis for many years, and it is debated whether it helps.
Traditional use
Carnitine is a vitamin-like compound the body makes from the amino acids lysine and methionine. It is also in food, mostly meat. It is not a vitamin and is not essential in the usual sense, because the body can make it.
Proposed mechanism Not established
Not examined in the abstract.
A proposed mechanism does not show that the effect happens in people.
People with kidney failure should ask their kidney team before any supplement.
Connections to the rest of health
How Carnitine 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 |
|---|---|---|---|---|
| Balanced Nutrition | High certainty | What carnitine does in the body and where it comes from: Carnitine carries fats into the cell's energy units so they can be burned for energy. People who eat meat get about three quarters of their carnitine from food; the body makes the rest. | 1 9 8 | |
| Energy Boost | High certainty | What carnitine does in the body and where it comes from: Carnitine carries fats into the cell's energy units so they can be burned for energy. People who eat meat get about three quarters of their carnitine from food; the body makes the rest. | 1 9 8 | |
| Weight Management | Low certainty | Body weight and body fat: Across dozens of trials, L-carnitine pills gave a small average fall in weight: about 1 kg more than placebo. The effect was seen mainly in people with overweight or obesity. | 16 2 | |
| Metabolic Health | Low certainty | Body weight and body fat: Across dozens of trials, L-carnitine pills gave a small average fall in weight: about 1 kg more than placebo. The effect was seen mainly in people with overweight or obesity. | 16 2 | |
| Preventive Wellness | High certainty | Inherited carnitine shortage: Rare inherited conditions stop the body from making, absorbing or using carnitine. They can cause low blood sugar, a weak heart and liver problems. These need medical care, not shop supplements. | 1 18 | |
| Brain Health | Very low certainty | Painful nerve damage (acetyl-L-carnitine): Acetyl-L-carnitine, a form made from carnitine, has been tested for pain from nerve damage caused by diabetes or HIV medicines. One review says it helped; a stricter review says the evidence is very uncertain. | 4 13 | |
| Healthy Aging | Very low certainty | Painful nerve damage (acetyl-L-carnitine): Acetyl-L-carnitine, a form made from carnitine, has been tested for pain from nerve damage caused by diabetes or HIV medicines. One review says it helped; a stricter review says the evidence is very uncertain. | 4 13 | |
| Heart Health | Low certainty | After a heart attack: A 2013 review of 13 trials found fewer deaths, fewer abnormal heart rhythms and less angina with carnitine in people who had a heart attack. The death result was borderline and the authors call for new trials. Chronic heart failure: A 2017 review of 17 trials found better heart pumping measures and lower BNP markers with L-carnitine added to usual care, but no clear difference in deaths or in the 6-minute walk. | 5 15 | |
| Memory Support | Not enough evidence | Dementia and memory (acetyl-L-carnitine): A Cochrane review of 11 trials in Alzheimer's disease found no benefit on thinking, severity or daily function. It is an older review (searched to 2003). | 6 | |
| Brain Health | Not enough evidence | Dementia and memory (acetyl-L-carnitine): A Cochrane review of 11 trials in Alzheimer's disease found no benefit on thinking, severity or daily function. It is an older review (searched to 2003). | 6 | |
| Preventive Wellness | Low certainty | Male infertility (sperm quality): In men with infertility of unknown cause, L-carnitine or acetyl-L-carnitine improved sperm movement and shape in 8 trials, but did not raise sperm count or clearly raise pregnancy rates. Liver blood tests: A 2020 meta-analysis of 18 trials found lower blood liver-enzyme levels (ALT, AST, GGT) with L-carnitine. These are blood tests, not proof of better liver health. | 7 12 | |
| Sports Performance | Low certainty | Exercise performance and recovery: Eleven small trials gave mixed results. Some found better results in short, hard exercise; none found improvements in moderate exercise. | 10 14 | |
| Physical Stamina | Low certainty | Exercise performance and recovery: Eleven small trials gave mixed results. Some found better results in short, hard exercise; none found improvements in moderate exercise. | 10 14 | |
| Blood Sugar Balance | Low certainty | Blood sugar and cholesterol in type 2 diabetes: A 2024 meta-analysis of 21 trials found small average falls in HbA1c, fasting glucose and LDL cholesterol in people with type 2 diabetes. Results differed a lot between trials. | 11 | |
| Cholesterol Balance | Low certainty | Blood sugar and cholesterol in type 2 diabetes: A 2024 meta-analysis of 21 trials found small average falls in HbA1c, fasting glucose and LDL cholesterol in people with type 2 diabetes. Results differed a lot between trials. | 11 | |
| Preventive Wellness | Not enough evidence | People having long-term kidney dialysis: A 2014 meta-analysis found no clear improvement from L-carnitine in quality of life, inflammation, anaemia or cholesterol in people on haemodialysis. | 17 2 |
B. Body systems
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Whole Body | Biological association | High certainty | Studied for: What carnitine does in the body and where it comes from Studied for: Body weight and body fat | 1 9 8 16 2 |
| Metabolism | Biological association | High certainty | Studied for: What carnitine does in the body and where it comes from Studied for: Inherited carnitine shortage | 1 9 8 18 |
| Metabolism Weight | Biological association | Low certainty | Studied for: Body weight and body fat | 16 2 |
| Cardiovascular System | Biological association | High certainty | Studied for: Inherited carnitine shortage Studied for: After a heart attack | 1 18 5 15 |
| Nervous System | Biological association | Very low certainty | Studied for: Painful nerve damage (acetyl-L-carnitine) Studied for: Dementia and memory (acetyl-L-carnitine) | 4 13 6 |
| Heart Circulation | Biological association | Low certainty | Studied for: After a heart attack | 5 |
| Reproductive System | Biological association | Low certainty | Studied for: Male infertility (sperm quality) | 7 |
| Musculoskeletal System | Biological association | Low certainty | Studied for: Exercise performance and recovery | 10 14 |
| Metabolic System | Biological association | Low certainty | Studied for: Blood sugar and cholesterol in type 2 diabetes | 11 |
| Endocrine System | Biological association | Low certainty | Studied for: Blood sugar and cholesterol in type 2 diabetes | 11 |
| Hepatic System | Biological association | Low certainty | Studied for: Liver blood tests | 12 |
| Kidney Urinary | Biological association | Not enough evidence | Studied for: People having long-term kidney dialysis | 17 2 |
I. Biomarkers
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Body weight (kg) | Biological association | Low certainty | Measured in trials: lower (small). A lab change is not the same as a health benefit. | 16 2 |
| Fat mass (kg) | Biological association | Low certainty | Measured in trials: lower (small). A lab change is not the same as a health benefit. | 16 2 |
| Nerve pain score | Biological association | Very low certainty | Measured in trials: lower (very uncertain). A lab change is not the same as a health benefit. | 4 13 |
| Heart ejection fraction | Biological association | Low certainty | Measured in trials: higher (small). A lab change is not the same as a health benefit. | 15 |
| HbA1c | Biological association | Low certainty | Measured in trials: lower (small). A lab change is not the same as a health benefit. | 11 |
| LDL cholesterol | Biological association | Low certainty | Measured in trials: lower (small). A lab change is not the same as a health benefit. | 11 |
| Liver enzymes ALT and AST | Biological association | Moderate certainty | Measured in trials: lower. A lab change is not the same as a health benefit. | 12 |
| Sperm motility and shape | Biological association | Low certainty | Measured in trials: higher. A lab change is not the same as a health benefit. | 7 |
| Quality of life in dialysis (SF-36) | Biological association | Not enough evidence | Measured in trials: no clear change. A lab change is not the same as a health benefit. | 17 |
J. Genes, receptors and enzymes
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| SLC22A5 (OCTN2 carnitine transporter) | Preliminary mechanism | Human | Changes in this gene cause primary carnitine deficiency (MedlinePlus Genetics). | 18 |
K. Biological pathways
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| Lysine | Preliminary mechanism | Human | A building block the body uses to make carnitine. | 1 |
L. Active compounds
| Connected to | Kind of connection | Evidence status | Context | Studies |
|---|---|---|---|---|
| L-carnitine | Biological association | Human | The form tested for body weight, heart conditions, diabetes markers, liver enzymes and sperm quality. | 16 5 15 11 |
| Acetyl-L-carnitine (ALC) | Biological association | Human | Derived from carnitine; tested for nerve pain and dementia. | 13 6 |
| Trimethylamine-N-oxide (TMAO) | Biological association | Mouse and human observational | Made when gut bacteria and the liver process carnitine (and choline); linked to artery disease in mice and in observational human data. | 8 9 |
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 12 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 Carnitine. 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 carnitine summary, read MedlinePlus Genetics, and re-read PubMed abstracts for reviews, trials and mechanism studies. Only abstracts were read for studies. The NIH Office of Dietary Supplements page was blocked and is marked unread.
Study library: every study we checked 19
| Study | Design | People | Product, dose, length | Result |
|---|---|---|---|---|
| Almannai 2019 Carnitine Inborn Errors of Metabolism. Molecules · PMID 31500110 · DOI |
Narrative review |
Review of carnitine biology and the inherited disorders of carnitine making, transport and use | Carnitine (the body's own, and from food) |
Reviews how carnitine moves fats into the cell's energy units (mitochondria). In people who eat meat, about 75% of the body's carnitine comes from food and about 25% is made in the body from lysine and methionine. Inherited disorders cause low blood sugar without ketones, heart muscle disease and liver disease. No numbers beyond the 75% / 25% split (Not applicable) Methods, limits and fundingOutcomes: How the body makes, takes in and uses carnitine; inherited disorders Limitations: A narrative review, read from the abstract only. Funding and conflicts: Authors declare no conflicts of interest. Read: abstract |
| Askarpour 2020 Beneficial effects of l-carnitine supplementation for weight management in overweight and obese adults: An updated systematic review and dose-response meta-analysis of randomized controlled trials. Pharmacol Res · PMID 31743774 · DOI |
Systematic review meta analysis |
43 randomised trials; effects seen only in people with overweight or obesity; no change in people having haemodialysis | L-carnitine (oral) Supplement Varied by trial Varied by trial · vs Placebo or control |
Small average falls in weight, BMI and fat mass. No clear change in body fat percent or waist. Weight and BMI fell only in overweight or obese people, and when carnitine was combined with lifestyle changes. Weight WMD -1.129 kg; BMI -0.359 kg/m2; fat mass -1.158 kg (Weight -1.590 to -0.669; BMI -0.552 to -0.167; fat mass -1.763 to -0.554) Methods, limits and fundingOutcomes: Weight, BMI, fat mass, body fat percent, waist Limitations: Large differences between trials (I2 63% for weight and 85% for BMI); read from the abstract only; the number of people was not in the abstract. Funding and conflicts: Funding and conflicts are not stated in the abstract. Read: abstract |
| Benvenga 2001 Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab · PMID 11502782 · DOI |
Randomised controlled trial |
50 50 women taking a fixed thyroid-suppressing dose of levothyroxine (L-T4) |
L-carnitine (oral) Supplement 2 g or 4 g a day were studied in the trial 6 months · vs Placebo |
Symptoms and blood markers of too much thyroid hormone worsened on placebo and improved or stayed level while taking carnitine. The authors say carnitine opposes thyroid hormone action in some tissues. For a person taking thyroid medicine this means carnitine may work against the medicine. Group-level changes; the abstract gives no pooled numbers (Not given in the abstract) Methods, limits and fundingOutcomes: Nine hyperthyroid-type symptoms, nine thyroid-sensitive blood tests, bone density Limitations: Small trial, 10 women per group, single group of authors; it studied women taking too much thyroid hormone on purpose, not people on a normal replacement dose. Funding and conflicts: Funding and conflicts are not stated in the abstract. Read: abstract |
| Di Stefano 2019 Acetyl-L-carnitine in painful peripheral neuropathy: a systematic review. J Pain Res · PMID 31118753 · DOI |
Systematic review |
14 clinical trials reviewed; a pooled analysis of 4 randomised trials in nerve damage from diabetes or from HIV drugs | Acetyl-L-carnitine (oral) Supplement Trial detail not given in the abstract Varied · vs Placebo |
Pooled pain fell by about 20% from baseline more than with placebo. The authors call it effective and safe, and ask for studies of the best amount and length. Pain reduction 20.2% more than placebo (95% CI 8.3% to 32.1%) Methods, limits and fundingOutcomes: Pain on a 10 cm scale; nerve conduction; safety Limitations: This is a review by authors, several of whom report fees from the manufacturer; a stricter 2019 Cochrane review rated the same kind of evidence very uncertain. Funding and conflicts: Several authors report research grants, consulting fees or lecture fees from Sigma-Tau (Alfasigma), the maker of acetyl-L-carnitine, and other drug companies. Read: abstract |
| DiNicolantonio 2013 L-carnitine in the secondary prevention of cardiovascular disease: systematic review and meta-analysis. Mayo Clin Proc · PMID 23597877 · DOI |
Systematic review meta analysis |
3629 13 controlled trials, 3,629 people who had had a heart attack |
L-carnitine (oral or by injection; the abstract does not say) Supplement or treatment Not given in the abstract Not given in the abstract · vs Placebo or control |
Fewer deaths, fewer abnormal rhythms and less angina were seen with carnitine. No clear fall in heart failure or second heart attacks. The authors say big modern trials are needed. All-cause death OR 0.73; ventricular arrhythmias RR 0.35; angina RR 0.60; heart failure RR 0.85 (not significant); reinfarction RR 0.78 (not significant) (Death 0.54 to 0.99; arrhythmias 0.21 to 0.58; angina 0.50 to 0.72; heart failure 0.67 to 1.09; reinfarction 0.41 to 1.48) Methods, limits and fundingOutcomes: Death from any cause, abnormal heart rhythms, angina, heart failure, second heart attack Limitations: Trials differed in design; the death result only just reached significance; the authors call for large trials in the modern era. Funding and conflicts: Funding and conflicts are not stated in the abstract. Read: abstract |
| Hudson 2003 Acetyl-L-carnitine for dementia. Cochrane Database Syst Rev · PMID 12804452 · DOI |
Systematic review meta analysis |
11 trials, all in people with Alzheimer's disease | Acetyl-L-carnitine (oral) Supplement Not given in the abstract Not given in the abstract · vs Placebo |
No benefit on thinking, severity or daily function. A benefit on one doctor-rated global score at 12 and 24 weeks (not at 52 weeks) may be due to chance, because so many comparisons were made. No routine use recommended. Clinical global impression: OR 2.33 at 12 weeks and OR 3.91 at 24 weeks; no benefit on other measures (95% CI 1.25 to 4.35 (12 weeks); 1.32 to 11.54 (24 weeks)) Methods, limits and fundingOutcomes: Thinking (cognition), dementia severity, daily function, clinical global impression Limitations: Old review (search to January 2003); mostly completer analyses. Funding and conflicts: Conflict of interest: none known. Read: abstract |
| Khaw 2020 l-carnitine and l-acetylcarnitine supplementation for idiopathic male infertility. Reprod Fertil · PMID 35128424 · DOI |
Systematic review meta analysis |
8 randomised trials in men with infertility of unknown cause | L-carnitine or L-acetylcarnitine (oral) Supplement Not given in the abstract Not given in the abstract · vs Placebo or no treatment |
Better total and forward sperm movement and more normally shaped sperm. No effect on sperm count. No clear effect on pregnancy (5 trials; few people). Not given as numbers in the abstract (Not given in the abstract) Methods, limits and fundingOutcomes: Sperm motility, shape, concentration; pregnancy Limitations: Few trials and few pregnancies; sperm tests are not the same as having a baby. Funding and conflicts: One author has received research funding from AstraZeneca; the others declare none. Read: abstract |
| Koeth 2013 Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med · PMID 23563705 · DOI |
Mixed human and animal human-and-mouse |
2595 Mice; a small number of omnivores, vegans and vegetarians given carnitine; and 2,595 people having a heart check-up |
L-carnitine (dietary) Dietary and supplement carnitine Not given in the abstract Mouse feeding was long-term (chronic) |
Gut bacteria turn carnitine into TMAO. In mice, carnitine feeding raised TMAO and increased artery plaque, but not when gut bacteria were suppressed. People who eat meat made more TMAO than vegans or vegetarians after carnitine. In 2,595 people, high blood carnitine predicted more heart disease and heart events only when TMAO was also high. Not given as numbers in the abstract (Not applicable) Methods, limits and fundingOutcomes: Gut-made TMAO; hardening of the arteries in mice; heart events in people Limitations: Mouse results do not show the same happens in people; the human link is observational. Funding and conflicts: Funding is not stated in the abstract. The first author also wrote the 2019 paper, whose authors report patents and industry ties. Read: abstract |
| Koeth 2019 l-Carnitine in omnivorous diets induces an atherogenic gut microbial pathway in humans. J Clin Invest · PMID 30530985 · DOI |
Clinical trial |
72 Omnivores (n=40) and vegans or vegetarians (n=32) who took labelled carnitine, some also after antibiotics or after 2 months of carnitine |
Labelled L-carnitine (d3-L-carnitine) and gamma-butyrobetaine Supplement (tracer) Not given in the abstract Single doses and a 2-month or longer carnitine course · vs Before versus after antibiotics |
After a carnitine dose, omnivores made more than 20 times as much TMAO as vegans or vegetarians. Gut bacteria do the first steps. The second gut step is switched on by an omnivorous diet and by regular carnitine. TMAO more than 20-fold higher in omnivores (P = 0.001) (Not given in the abstract) Methods, limits and fundingOutcomes: Blood levels of carnitine breakdown products, including TMAO Limitations: A mechanism study of blood chemistry; it did not measure heart disease in these people. Funding and conflicts: Funded by NIH, the NIH Office of Dietary Supplements and the Leducq Foundation. Several authors are named on Cleveland Clinic patents and have received royalties or consulting or research funds from Procter & Gamble and others; some authors are Procter & Gamble employees. Read: abstract |
| Mielgo-Ayuso 2021 Effect of Acute and Chronic Oral l-Carnitine Supplementation on Exercise Performance Based on the Exercise Intensity: A Systematic Review. Nutrients · PMID 34959912 · DOI |
Systematic review |
11 trials in healthy people and athletes | L-carnitine, L-carnitine L-tartrate or glycine-propionyl-L-carnitine (oral) Supplement Single doses of 3 to 4 g and daily amounts of 1 to 3 g for 4 to 24 weeks were studied Single dose or 4 to 24 weeks · vs Placebo |
Some trials found better results in hard, high-intensity exercise (less effort felt, more power in short all-out tests). No improvement in moderate-intensity exercise. No pooled numbers (a narrative review) (Not applicable) Methods, limits and fundingOutcomes: High-intensity and moderate-intensity exercise performance Limitations: Only 11 small trials, each with different tests; no pooled analysis. Funding and conflicts: Authors declare no conflict of interest. Read: abstract |
| Mirrafiei 2024 The Effects of L-Carnitine Supplementation on Weight Loss, Glycemic Control, and Cardiovascular Risk Factors in Patients With Type 2 Diabetes: A Systematic Review and Dose-response Meta-Analysis of Randomized Controlled Trials. Clin Ther · PMID 38594107 · DOI |
Systematic review meta analysis |
2041 21 randomised trials, 2,041 adults with type 2 diabetes |
L-carnitine (oral) Supplement Results are reported per 1 g a day in the trials Varied by trial · vs Placebo or control |
Small average falls in HbA1c, fasting glucose, LDL cholesterol and BMI. The authors warn that the results differ a lot between trials and should be read very cautiously. Per 1 g/day: HbA1c MD -0.16%; LDL MD -0.11 mmol/L; fasting glucose MD -0.17 mmol/L; BMI MD -0.37 kg/m2 (HbA1c -0.32 to -0.01; LDL -0.16 to -0.05; BMI -0.59 to -0.15) Methods, limits and fundingOutcomes: BMI, HbA1c, fasting glucose, LDL cholesterol, triglycerides, total cholesterol Limitations: Very large differences between trials (I2 91% to 94%); the authors graded HbA1c moderate, LDL high and BMI low. Funding and conflicts: Authors declare no competing interests. Read: abstract |
| Pirmadah 2020 Does L-carnitine supplementation affect serum levels of enzymes mainly produced by liver? A systematic review and meta-analysis of randomized controlled clinical trials. Eur J Nutr · PMID 31385062 · DOI |
Systematic review meta analysis |
1161 18 randomised trials, 1,161 people |
L-carnitine (oral) Supplement Trials studied 500 to 4,000 mg a day; the effect was larger at 2,000 mg a day or more and in people with liver disease Varied · vs Placebo or control |
Lower blood ALT, AST and GGT. This is a blood-test result; it does not show better liver health outcomes. ALT MD -8.65 IU/L; AST MD -8.52 IU/L; GGT MD -8.80 IU/L (ALT -13.40 to -3.90; AST -12.16 to -4.89; GGT -13.67 to -3.92) Methods, limits and fundingOutcomes: Blood liver enzymes ALT, AST and GGT Limitations: Blood markers only; the authors ask for better trials. They rated ALT and AST moderate and GGT low. Funding and conflicts: Funding and conflicts are not stated in the abstract. Read: abstract |
| Rolim 2019 Acetyl-L-carnitine for the treatment of diabetic peripheral neuropathy. Cochrane Database Syst Rev · PMID 31201734 · DOI |
Systematic review meta analysis |
907 4 trials, 907 people with diabetic nerve damage (neuropathy); 3 against placebo |
Acetyl-L-carnitine (oral) Supplement Trials used amounts from 1,500 to 3,000 mg a day (studied in the trials) 6 to 12 months · vs Placebo; one trial used methylcobalamin |
Pain was a little lower than with placebo (mean difference -9.16 mm of 100) but the reviewers rate this very-low certainty and are very uncertain whether it reduces pain. Side effects were headache, facial tingling and stomach upset; the evidence on safety is too uncertain. Pain on 0 to 100 mm scale: mean difference -9.16 versus placebo (95% CI -16.76 to -1.57) Methods, limits and fundingOutcomes: Pain on a 0 to 100 mm scale; vibration sense; disability; side effects Limitations: Very-low certainty; high risk of bias in two trials; data on function and symptoms lacking. Funding and conflicts: Two trials were funded by the manufacturer of acetyl-L-carnitine and two others had at least one author who was a consultant for a manufacturer. Read: abstract |
| Sawicka 2020 The bright and the dark sides of L-carnitine supplementation: a systematic review. J Int Soc Sports Nutr · PMID 32958033 · DOI |
Systematic review |
11 studies in healthy people taking oral L-carnitine for at least 12 weeks | L-carnitine (oral) Supplement 1 to 4 g a day for 12 or 24 weeks were studied 12 to 24 weeks · vs Placebo or no supplement |
Carnitine with carbohydrate raised carnitine in muscle. In very old women (centenarians), 24 weeks raised muscle mass and improved effort tolerance and thinking; muscle strength was unchanged in older women. Fasting blood TMAO rose, with no change in the inflammation or oxidation markers measured. The authors say long-term heart effects still need study. No pooled numbers in the abstract (Not applicable) Methods, limits and fundingOutcomes: Muscle carnitine, muscle mass and strength, effort tolerance, TMAO, inflammation and oxidation markers Limitations: Small studies in healthy people; only 11 studies; effects on heart disease were not measured. Funding and conflicts: Authors declare no competing interests. Read: abstract |
| Song 2017 Efficacy and Safety of L-Carnitine Treatment for Chronic Heart Failure: A Meta-Analysis of Randomized Controlled Trials. Biomed Res Int · PMID 28497060 · DOI |
Systematic review meta analysis |
1625 17 randomised trials, 1,625 people with chronic heart failure |
L-carnitine added to usual heart-failure care Treatment alongside usual care Not given in the abstract Not given in the abstract · vs Usual care or placebo |
Better ejection fraction, stroke volume and cardiac output, and lower BNP markers. No clear difference in death from any cause, in the 6-minute walk, or in side effects. Ejection fraction WMD +4.14 percentage points; NT-proBNP WMD -510 pg/ml; death: no significant difference (Not given in the abstract for most results) Methods, limits and fundingOutcomes: Heart pumping (ejection fraction), blood markers BNP and NT-proBNP, death, 6-minute walk, side effects Limitations: The abstract does not describe trial quality; improvements were in heart measures, not in survival. Funding and conflicts: Funding and conflicts are not stated in the abstract. Read: abstract |
| Talenezhad 2020 Effects of l-carnitine supplementation on weight loss and body composition: A systematic review and meta-analysis of 37 randomized controlled clinical trials with dose-response analysis. Clin Nutr ESPEN · PMID 32359762 · DOI |
Systematic review meta analysis |
2292 37 randomised trials in adults (2,292 people); the effect was clearer in adults with overweight or obesity |
L-carnitine (oral) Supplement (forms and products varied) Trial amounts varied; the authors report a curved dose-response Varied by trial · vs Placebo or control |
Small average falls in weight, BMI and fat mass. No clear effect on waist or body fat percent. The result for weight held when only high-quality trials were pooled. Weight WMD -1.21 kg; BMI -0.24 kg/m2; fat mass -2.08 kg (Weight -1.73 to -0.68; BMI -0.37 to -0.10; fat mass -3.44 to -0.72) Methods, limits and fundingOutcomes: Body weight, BMI, fat mass, waist, body fat percent Limitations: A modest average change; trial quality and products varied; read from the abstract only. Funding and conflicts: Authors declare no conflict of interest. Read: abstract |
| Yang 2014 Effect of L-carnitine therapy on patients in maintenance hemodialysis: a systematic review and meta-analysis. J Nephrol · PMID 24535997 · DOI |
Systematic review meta analysis |
Randomised trials in people having long-term haemodialysis | L-carnitine versus placebo Supplement or treatment Not given in the abstract Not given in the abstract · vs Placebo |
No clear improvement in quality of life, inflammation, nutrition, anaemia, cholesterol or parathyroid hormone. The authors note methodological limits and a lack of hard endpoints. No significant pooled change (e.g. SF-36 SMD 0.76; CRP SMD -0.37) (SF-36 -0.13 to 1.65; CRP -0.88 to 0.14) Methods, limits and fundingOutcomes: Quality of life (SF-36), CRP, albumin, haemoglobin, cholesterol, triglycerides, parathyroid hormone Limitations: Small trials and no hard endpoints; read from the abstract only; a 2014 review. Funding and conflicts: Funding and conflicts are not stated in the abstract. Read: abstract |
| s-medlineplus-pcd MedlinePlus Genetics: Primary carnitine deficiency (page updated 2023-11-27) · Source |
Reference database n/a |
Methods, limits and fundingRead: full-text | ||
| s-ods-carnitine NIH Office of Dietary Supplements: Carnitine fact sheet for health professionals · Source |
Reference database n/a |
Methods, limits and fundingRead: not-read |
What we do not know yet
- No source read gives carnitine amounts per portion of food (the NIH fact sheet was blocked).
- No large modern trial of carnitine after a heart attack was read.
- Long-term effects of carnitine pills on the heart were not shown either way.
- Pregnancy, breastfeeding and children were not covered by any source read.
- Interactions with medicines other than thyroid hormone were not studied in the sources read.
- Product quality and label accuracy 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 2
HbA1c
Lower (small) in trials
A blood test showing average blood sugar over about three months.
Low certaintyResults and what it means
Why it was measured
To see whether carnitine lowers long-term blood sugar in type 2 diabetes.
Statistical vs. clinical meaning
Small change; trials differ greatly.
Safety implication
Do not change diabetes medicine without a doctor.
| Study | Result | People | Product |
|---|---|---|---|
| 11 | Mean difference -0.16% per 1 g/day (95% CI -0.32 to -0.01); authors' GRADE moderate; I2 94% | 21 trials, 2,041 adults with type 2 diabetes | L-carnitine by mouth |
LDL cholesterol
Lower (small) in trials
The "bad" cholesterol carried in the blood.
Low certaintyResults and what it means
Why it was measured
To see whether carnitine lowers LDL in type 2 diabetes.
Statistical vs. clinical meaning
Small change; trials differ greatly.
Safety implication
Ask a doctor about cholesterol medicine.
| Study | Result | People | Product |
|---|---|---|---|
| 11 | Mean difference -0.11 mmol/L per 1 g/day (95% CI -0.16 to -0.05); authors' GRADE high; I2 91% | 11 trials in type 2 diabetes | L-carnitine by mouth |
Other 7
Body weight (kg)
Lower (small) in trials
Total weight of the body in kilograms.
Low certaintyResults and what it means
Why it was measured
To see whether L-carnitine pills change weight.
Statistical vs. clinical meaning
About a kilogram on average; trials differed a lot.
Safety implication
Not a reason to take pills for weight loss without asking a doctor.
| Study | Result | People | Product |
|---|---|---|---|
| 16 | Weighted mean difference -1.21 kg (95% CI -1.73 to -0.68) versus control | 37 randomised trials, 2,292 adults | L-carnitine pills, forms and amounts varied |
| 2 | Weighted mean difference -1.129 kg (95% CI -1.590 to -0.669) | 43 randomised trials; only people with overweight or obesity had the fall | L-carnitine pills, forms and amounts varied |
Fat mass (kg)
Lower (small) in trials
The weight of body fat, measured by scans or special scales.
Low certaintyResults and what it means
Why it was measured
To see whether any weight lost was fat.
Statistical vs. clinical meaning
Small average fall; body fat percent and waist did not change clearly in either review.
Safety implication
As above.
Nerve pain score
Lower (very uncertain) in trials
Pain rated by the patient on a scale from 0 (none) to 100 mm or 10 cm.
Very low certaintyResults and what it means
Why it was measured
To see whether acetyl-L-carnitine lowers pain from nerve damage.
Statistical vs. clinical meaning
Small and uncertain; reviewers disagree on how strong the evidence is.
Safety implication
Headache, facial tingling and stomach upset were reported.
| Study | Result | People | Product |
|---|---|---|---|
| 13 | Mean difference -9.16 mm on a 0 to 100 mm scale (95% CI -16.76 to -1.57); very-low certainty | 3 trials against placebo, 540 people with diabetic neuropathy | Acetyl-L-carnitine by mouth |
| 4 | Pain reduction 20.2% versus placebo (95% CI 8.3% to 32.1%) | 4 randomised trials (diabetes or HIV drug neuropathy) | Acetyl-L-carnitine by mouth |
Heart ejection fraction
Higher (small) in trials
The share of blood the heart pumps out with each beat, measured by an ultrasound scan.
Low certaintyResults and what it means
Why it was measured
To see whether carnitine improves how well a failing heart pumps.
Statistical vs. clinical meaning
A measurement change; no clear change in deaths or in the 6-minute walk.
Safety implication
No difference in side effects in the pooled trials.
| Study | Result | People | Product |
|---|---|---|---|
| 15 | Weighted mean difference +4.14 percentage points (P = 0.01); NT-proBNP -510.36 pg/ml (P < 0.01) | 17 randomised trials, 1,625 people with chronic heart failure | L-carnitine added to usual care |
Liver enzymes ALT and AST
Lower in trials
Enzymes that leak from liver cells into the blood; high levels can signal liver strain.
Moderate certaintyResults and what it means
Why it was measured
To see whether carnitine lowers liver strain markers.
Statistical vs. clinical meaning
A blood-marker change rated moderate by the reviewers; its meaning for liver health is unproven.
Safety implication
Raised liver enzymes need a doctor's review.
| Study | Result | People | Product |
|---|---|---|---|
| 12 | ALT -8.65 IU/L (-13.40 to -3.90); AST -8.52 IU/L (-12.16 to -4.89); reviewers' NutriGrade moderate | 18 trials, 1,161 people | L-carnitine by mouth |
Sperm motility and shape
Higher in trials
How well sperm swim and how many have a normal shape, measured in a semen test.
Low certaintyResults and what it means
Why it was measured
To see whether carnitine improves sperm quality.
Statistical vs. clinical meaning
Better semen tests; no proof of more pregnancies.
Safety implication
No specific harms reported in the abstract.
| Study | Result | People | Product |
|---|---|---|---|
| 7 | Significant improvement in total motility, progressive motility and morphology; no effect on concentration or clinical pregnancy | 8 randomised trials, men with unexplained infertility | L-carnitine or L-acetylcarnitine by mouth |
Quality of life in dialysis (SF-36)
No clear change in trials
A questionnaire scoring physical and mental well-being.
Not enough evidenceResults and what it means
Why it was measured
To see whether carnitine improves how people on dialysis feel.
Statistical vs. clinical meaning
No clear benefit shown.
Safety implication
None specific to this measure.
| Study | Result | People | Product |
|---|---|---|---|
| 17 | SF-36 total score SMD 0.76 (95% CI -0.13 to 1.65, P = 0.09): not significant | Trials in haemodialysis patients | L-carnitine versus placebo |
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
- Gut bacteria turn carnitine into TMAO, a substance linked to artery disease. When carnitine reaches the gut, bacteria change it into TMA, which the liver turns into TMAO. In mice, carnitine feeding raised TMAO and increased artery plaque, but not when gut bacteria were suppressed. In a 2019 human tracer study, people who eat meat made more than 20 times as much TMAO after a carnitine dose as vegans or vegetarians. A 2013 study of 2,595 people having a heart check found high blood carnitine predicted heart events only when TMAO was also high. A 2020 review of long-term carnitine trials in healthy people found fasting TMAO rose, with no change in the inflammation or oxidation markers measured. None of this shows that carnitine pills cause heart disease in people; the human data are blood chemistry and observational. People with heart disease should ask a doctor before using carnitine. Mouse study, human tracer study, observational study and systematic review 8 9 14
- Carnitine may work against thyroid medicine. In a 6-month randomised trial of 50 women taking a fixed dose of levothyroxine (thyroid hormone), L-carnitine reduced or prevented symptoms of too much thyroid hormone, and the authors say carnitine opposes thyroid hormone in some tissues. For a person taking thyroid medicine this suggests carnitine could make the medicine less effective. The women were on a dose chosen to suppress TSH. Ask the prescriber before using carnitine with thyroid medicine. Randomised controlled trial (small) 3
- A true carnitine shortage is a medical emergency, not a supplement question. Inherited carnitine disorders can cause very low blood sugar, a weak and enlarged heart, liver disease and sudden death, and can be set off by fasting or infections (MedlinePlus Genetics). These need a specialist. Review and health information page 1 18
- Acetyl-L-carnitine side effects in nerve-pain trials. In the Cochrane review of diabetic nerve damage, side effects that led people to stop were headache, facial tingling and stomach or bowel problems. In one trial 6 of 147 people (4.1%) taking acetyl-L-carnitine and 2 of 147 (1.4%) taking placebo stopped because of side effects. The reviewers say the evidence is too uncertain to judge safety. Systematic review 13
Side effects 3
| Effect | How often | Severity and recovery | Evidence |
|---|---|---|---|
| Stomach and bowel upset, headache, facial tingling (acetyl-L-carnitine) The Cochrane reviewers rate the evidence on side effects as low certainty and too uncertain to judge safety. Two trials were funded by the manufacturer. | One diabetic-neuropathy trial: stopped because of side effects 4.1% (6 of 147) with acetyl-L-carnitine versus 1.4% (2 of 147) with placebo, P = 0.17. Another trial compared with methylcobalamin: adverse events in 29.1% versus 28.7%. | Mostly mild; some people stopped Not stated in the abstract. | Systematic review (Cochrane) 13 |
| Higher gut-made TMAO The 2019 tracer study is by authors with patents and industry ties. | Fasting blood TMAO rose in long-term carnitine studies in healthy people (review of 11 studies); more than 20 times more TMAO after a carnitine dose in meat eaters than in vegans or vegetarians (tracer study). | A blood marker, not an illness Not studied. | Systematic review and clinical trial 14 9 |
| No difference in side effects in pooled heart-failure and dementia trials These are statements from abstracts; trial quality and size were not assessed here. | Heart failure (17 trials): no significant difference in adverse events. Dementia (11 trials): various events but no significant differences between groups. | Not graded Not applicable | Meta analyses 15 6 |
Liver
No liver injury from carnitine was found in the sources read. A 2020 meta-analysis found lower, not higher, blood liver enzymes. A liver-safety reference (LiverTox) was not opened for this page. 12
How often. No frequency was found.
Monitoring. No agency monitoring advice was found.
This is a safety connection. It is not evidence that Carnitine supports liver health.
Medicines and supplements 3
| With | Why it matters | Importance | Evidence | What to do |
|---|---|---|---|---|
| Thyroid hormone (levothyroxine) prescription | The trial authors say carnitine blocks thyroid hormone from entering cell nuclei in some tissues (their earlier observation). | In 50 women on a fixed TSH-suppressing dose, carnitine reduced or prevented symptoms of too much thyroid hormone. This suggests carnitine can work against thyroid medicine. | Randomised controlled trial Low certainty 3 | Ask the prescriber or a pharmacist before taking carnitine with thyroid medicine. Do not change the medicine yourself. |
| Choline and lecithin (same gut-bacteria pathway) supplement | Gut bacteria make TMA from both carnitine and choline; in mice, either one lowered reverse cholesterol transport. | Whether taking both adds up in people was not shown in the sources read. | Mouse study Very low certainty 8 | Ask a doctor if you have heart disease. |
| Blood thinners, diabetes medicines and other prescription drugs prescription | Not studied in the sources read. | No interaction study was found in the sources read. Absence of a study is not proof of safety. | None found Not enough evidence | Tell your pharmacist about any carnitine product. People with diabetes should ask before adding it. |
Who should check first 5
| Situation | Advice | Evidence |
|---|---|---|
| People with heart disease | The gut-bacteria TMAO question applies to them. Ask a cardiologist or doctor before using carnitine. | Mouse study, observational study and tracer study 8 9 14 |
| People taking thyroid medicine, or with an overactive thyroid | A trial found carnitine can work against thyroid hormone. Ask the prescriber. | Randomised controlled trial 3 |
| People with kidney failure or on dialysis | No clear benefit was found in a 2014 meta-analysis. Ask your kidney team. | Meta-analysis 17 |
| Pregnancy and breastfeeding | No source on carnitine in pregnancy or breastfeeding was read for this page (the NIH page was blocked). Ask a doctor or pharmacist before any supplement. | No source read 19 |
| Infants and children | MedlinePlus Genetics says primary carnitine deficiency usually shows in infancy or early childhood and needs medical care. No source on carnitine supplements for healthy children was read. Do not give carnitine to a child without a doctor's advice. | Health information page 18 |
Overdose, product quality and regulators
Summary. No source read gives an official upper limit or an overdose picture for carnitine. The NIH Office of Dietary Supplements fact sheet, which would normally give this, could not be opened.
Animal. Mouse feeding raised TMAO and plaque (see above).
High dose or long term signals. Fasting TMAO rose in long-term carnitine trials in healthy people (review of 11 studies).
Overdose response. Not found in the sources read.
Genotoxicity. Not researched.
Contamination and label accuracy of carnitine products were not researched for this page.
Different forms are not interchangeable. Carnitine products come as L-carnitine, acetyl-L-carnitine, L-carnitine L-tartrate and others. The reviews read studied different forms, so results do not carry from one to another. 13 16 10
| Body | Action | Date |
|---|---|---|
| MedlinePlus Genetics (US National Library of Medicine) (United States) | Describes primary carnitine deficiency: signs in infancy or early childhood (brain dysfunction, weak and enlarged heart, vomiting, muscle weakness, low blood sugar), about 1 in 100,000 newborns worldwide, risk of sudden death, and triggers such as fasting or infections. source | 2023-11-27 |
When to get medical help
- A baby or child who is very sleepy or floppy, vomiting, has fits, or may have low blood sugar, especially during fasting or an infection: get emergency medical help.
- Chest pain, fainting, a very fast or irregular heartbeat, or sudden breathlessness: call emergency services. Carnitine is not a treatment for these.
- Severe diarrhoea, vomiting or a swollen face after taking a supplement: stop it and get medical help.
- Signs of too much thyroid hormone (fast heartbeat, shaking, weight loss, sweating) in someone taking thyroid medicine and carnitine: see the prescriber.
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 carnitine?
Carnitine is a vitamin-like compound made in the body from the amino acids lysine and methionine. It carries fats into the cell's energy units so they can be burned. It is not a vitamin and is not essential in the usual sense, because the body makes it.
Where does carnitine come from?
Is carnitine the same as acetyl-L-carnitine?
Does carnitine help with weight loss?
Does carnitine help the heart?
What is the TMAO question?
Does acetyl-L-carnitine help nerve pain?
Does carnitine help memory or dementia?
A Cochrane review of 11 trials in Alzheimer's disease found no benefit on thinking or dementia severity. It is an older review.
Does carnitine help male fertility?
It improved sperm movement and shape in 8 trials but not sperm count, and pregnancy rates did not clearly rise.
Does carnitine work against any medicines?
In a small trial, carnitine worked against thyroid hormone in women taking levothyroxine. Ask the prescriber. No other interaction study was found in the sources read.
Is a carnitine shortage common?
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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 carnitine summary, read MedlinePlus Genetics, and re-read PubMed abstracts for reviews, trials and mechanism studies. Only abstracts were read for studies. The NIH Office of Dietary Supplements page was blocked and is 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. Several acetyl-L-carnitine and TMAO papers have manufacturer or industry ties, which are noted where stated.
Sources 19
Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.
- Almannai M, Alfadhel M, El-Hattab AW. Carnitine Inborn Errors of Metabolism.. Molecules. 2019. PMID 31500110. DOI 10.3390/molecules24183251. (abstract)
- Askarpour M, Hadi A, Miraghajani M, Symonds ME, Sheikhi A, Ghaedi E. Beneficial effects of l-carnitine supplementation for weight management in overweight and obese adults: An updated systematic review and dose-response meta-analysis of randomized controlled trials.. Pharmacol Res. 2020. PMID 31743774. DOI 10.1016/j.phrs.2019.104554. (abstract)
- Benvenga S, Ruggeri RM, Russo A, Lapa D, Campenni A, Trimarchi F. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial.. J Clin Endocrinol Metab. 2001. PMID 11502782. DOI 10.1210/jcem.86.8.7747. (abstract)
- Di Stefano G, Di Lionardo A, Galosi E, Truini A, Cruccu G. Acetyl-L-carnitine in painful peripheral neuropathy: a systematic review.. J Pain Res. 2019. PMID 31118753. DOI 10.2147/JPR.S190231. (abstract)
- DiNicolantonio JJ, Lavie CJ, Fares H, Menezes AR, O'Keefe JH. L-carnitine in the secondary prevention of cardiovascular disease: systematic review and meta-analysis.. Mayo Clin Proc. 2013. PMID 23597877. DOI 10.1016/j.mayocp.2013.02.007. (abstract)
- Hudson S, Tabet N. Acetyl-L-carnitine for dementia.. Cochrane Database Syst Rev. 2003. PMID 12804452. DOI 10.1002/14651858.CD003158. (abstract)
- Khaw SC, Wong ZZ, Anderson R, Martins da Silva S. l-carnitine and l-acetylcarnitine supplementation for idiopathic male infertility.. Reprod Fertil. 2020. PMID 35128424. DOI 10.1530/RAF-20-0037. (abstract)
- Koeth RA, Wang Z, Levison BS, Buffa JA, Org E, Sheehy BT, Britt EB, Fu X, Wu Y, Li L, Smith JD, DiDonato JA, Chen J, Li H, Wu GD, Lewis JD, Warrier M, Brown JM, Krauss RM, Tang WH, Bushman FD, Lusis AJ, Hazen SL. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis.. Nat Med. 2013. PMID 23563705. DOI 10.1038/nm.3145. (abstract)
- Koeth RA, Lam-Galvez BR, Kirsop J, Wang Z, Levison BS, Gu X, Copeland MF, Bartlett D, Cody DB, Dai HJ, Culley MK, Li XS, Fu X, Wu Y, Li L, DiDonato JA, Tang WHW, Garcia-Garcia JC, Hazen SL. l-Carnitine in omnivorous diets induces an atherogenic gut microbial pathway in humans.. J Clin Invest. 2019. PMID 30530985. DOI 10.1172/JCI94601. (abstract)
- Mielgo-Ayuso J, Pietrantonio L, Viribay A, Calleja-González J, González-Bernal J, Fernández-Lázaro D. Effect of Acute and Chronic Oral l-Carnitine Supplementation on Exercise Performance Based on the Exercise Intensity: A Systematic Review.. Nutrients. 2021. PMID 34959912. DOI 10.3390/nu13124359. (abstract)
- Mirrafiei A, Jayedi A, Shab-Bidar S. The Effects of L-Carnitine Supplementation on Weight Loss, Glycemic Control, and Cardiovascular Risk Factors in Patients With Type 2 Diabetes: A Systematic Review and Dose-response Meta-Analysis of Randomized Controlled Trials.. Clin Ther. 2024. PMID 38594107. DOI 10.1016/j.clinthera.2024.03.002. (abstract)
- Pirmadah F, Ramezani-Jolfaie N, Mohammadi M, Talenezhad N, Clark CCT, Salehi-Abargouei A. Does L-carnitine supplementation affect serum levels of enzymes mainly produced by liver? A systematic review and meta-analysis of randomized controlled clinical trials.. Eur J Nutr. 2020. PMID 31385062. DOI 10.1007/s00394-019-02068-4. (abstract)
- Rolim LC, da Silva EM, Flumignan RL, Abreu MM, Dib SA. Acetyl-L-carnitine for the treatment of diabetic peripheral neuropathy.. Cochrane Database Syst Rev. 2019. PMID 31201734. DOI 10.1002/14651858.CD011265.pub2. (abstract)
- Sawicka AK, Renzi G, Olek RA. The bright and the dark sides of L-carnitine supplementation: a systematic review.. J Int Soc Sports Nutr. 2020. PMID 32958033. DOI 10.1186/s12970-020-00377-2. (abstract)
- Song X, Qu H, Yang Z, Rong J, Cai W, Zhou H. Efficacy and Safety of L-Carnitine Treatment for Chronic Heart Failure: A Meta-Analysis of Randomized Controlled Trials.. Biomed Res Int. 2017. PMID 28497060. DOI 10.1155/2017/6274854. (abstract)
- Talenezhad N, Mohammadi M, Ramezani-Jolfaie N, Mozaffari-Khosravi H, Salehi-Abargouei A. Effects of l-carnitine supplementation on weight loss and body composition: A systematic review and meta-analysis of 37 randomized controlled clinical trials with dose-response analysis.. Clin Nutr ESPEN. 2020. PMID 32359762. DOI 10.1016/j.clnesp.2020.03.008. (abstract)
- Yang SK, Xiao L, Song PA, Xu X, Liu FY, Sun L. Effect of L-carnitine therapy on patients in maintenance hemodialysis: a systematic review and meta-analysis.. J Nephrol. 2014. PMID 24535997. DOI 10.1007/s40620-013-0002-7. (abstract)
- . MedlinePlus Genetics: Primary carnitine deficiency (page updated 2023-11-27). . . (full-text)
- . NIH Office of Dietary Supplements: Carnitine fact sheet for health professionals. . . (not-read)
Where to buy
Check the label first. Whatever you buy, look for these:
- The amount of the active ingredient per serving, not just the front-label claim
- A third-party testing mark (USP, NSF or ConsumerLab)
- Other ingredients and allergens
- Ask a pharmacist about interactions with your medicines
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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