Carnitine and Acetyl-L-Carnitine
Carnitine is an amino-acid-like compound made from lysine and methionine. Food sources, forms, weight-loss and acetyl-L-carnitine evidence, the TMAO question and safety points.
Content last updated . This page has not been medically reviewed.
What is Carnitine 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.
Moves fatty acids into mitochondria
Established roleCarnitine carries long-chain fatty acids into the cell's energy units (mitochondria) so they can be burned for energy.
Supplements: This is normal biology. The sources we read do not show extra carnitine improves energy in people with normal levels.
Body weight (L-carnitine)
Preliminary or mixedA meta-analysis of 37 trials found an average weight loss of about 1.2 kg with L-carnitine.
Supplements: Small average change; no significant effect on waist circumference or body fat percent.
Painful nerve damage (acetyl-L-carnitine)
Preliminary or mixedAcetyl-L-carnitine reduced pain by about 20% compared with placebo in four trials of nerve damage from diabetes and HIV treatment.
Supplements: Few trials; limited evidence. Results for one form should not be carried over to the other.
Dementia and memory (acetyl-L-carnitine)
Not enough evidenceA Cochrane review of 11 trials found no evidence of benefit on thinking or dementia severity.
Supplements: No evidence to recommend routine use for dementia.
Exercise performance and energy
Not enough evidenceWe found no proper evidence that carnitine supplements improve exercise performance.
Supplements: Insufficient evidence; the ISSN energy drink statement said benefits beyond caffeine and carbohydrate remain to be determined.
Replacing a rare inherited shortfall
Deficiency linkRare inherited carnitine disorders can cause low blood sugar, heart muscle disease and liver disease.
Supplements: Needs medical care, not shop supplements.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Health goals (2)
- Heart HealthDocumented risk
Gut-made TMAO from dietary carnitine promoted artery disease in mice; human data are observational. Not shown to cause heart disease from supplements, but people with heart disease should ask a clinician.
- Weight ManagementPreliminary or mixed
A meta-analysis of 37 trials (2,292 people) found about 1.2 kg average weight loss with L-carnitine; small effect, and no significant effect on waist or body fat percent.
Body systems (6)
- Energy & FatigueEstablished role
Carnitine carries long-chain fatty acids into the cell's energy units so they can be burned. This is its normal role; the sources we read do not show that extra carnitine raises energy or lowers tiredness.
- Metabolism & WeightEstablished role
Carnitine is needed to burn fat for fuel. A meta-analysis of 37 trials found an average weight loss of about 1.2 kg with L-carnitine, a small change.
- Cardiovascular SystemDocumented risk
Gut bacteria turn dietary carnitine into TMAO, which promoted artery disease in mice. This is a mechanistic and observational finding, not proof that supplements harm the heart; people with heart disease should ask a clinician.
- Endocrine SystemDocumented risk
In a 6-month trial in women taking thyroid hormone, L-carnitine reduced hyperthyroid-type symptoms, which suggests it can work against thyroid medicine. Ask a prescriber or pharmacist first.
- Heart & CirculationDocumented risk
Gut bacteria turn dietary carnitine into TMAO, which promoted artery disease in mice. This is a mechanistic and observational finding, not proof that supplements harm the heart.
- Nervous SystemPreliminary or mixed
Acetyl-L-carnitine has been studied for painful nerve damage with some pain reduction in a few trials, but a Cochrane review found no benefit for dementia.
Body parts (5)
- MitochondriaEstablished role
Carnitine shuttles long-chain fatty acids into the mitochondria, the cell's energy units, so they can be burned.
- HeartDeficiency link
In rare inherited carnitine disorders, findings include heart muscle disease. These need medical care and are not a reason to take shop supplements.
- LiverDeficiency link
In rare inherited carnitine disorders, findings include liver disease. These need medical care.
- Nervous SystemPreliminary or mixed
Acetyl-L-carnitine reduced pain in a few trials of nerve damage from diabetes and HIV treatment; evidence is limited.
- ThyroidDocumented risk
In one trial in women taking thyroid hormone, L-carnitine reduced hyperthyroid-type symptoms, suggesting it can work against thyroid medicine. Do not change medicine without asking a prescriber.
Functional actions (4)
- Mitochondrial SupportEstablished role
Carnitine moves fatty acids into the mitochondria. This is normal biology; extra supplements have not been shown to improve mitochondrial function in healthy people in the sources we read.
- Energy ProductionEstablished role
Carnitine helps the body use fat as fuel. Evidence that supplements improve exercise performance or energy is insufficient.
- Metabolic OptimizationPreliminary or mixed
L-carnitine was linked to a small average weight loss in a meta-analysis of 37 trials; no significant effect on waist or body fat percent.
- Pain ReliefPreliminary or mixed
Acetyl-L-carnitine gave a modest pain reduction compared with placebo in four trials of painful nerve damage; few trials.
Root causes (1)
- Nutrient DeficiencyDeficiency link
True carnitine deficiency is rare and mostly inherited. In vegans and vegetarians, fasting blood carnitine was similar to omnivores in one study.
Habits (1)
- Balanced NutritionEstablished role
In people who eat meat, about 75% of carnitine comes from food and about 25% from the body's own production.
Conditions & symptoms (3)
- Carnitine DeficiencyDeficiency link
Rare, mostly inherited carnitine disorders can cause low blood sugar, heart muscle disease and liver disease and need medical care.
- AtherosclerosisDocumented risk
Gut-made TMAO from dietary carnitine promoted atherosclerosis in mice; human findings are observational.
- Peripheral NeuropathyPreliminary or mixed
Acetyl-L-carnitine reduced pain in a few trials of nerve damage from diabetes and HIV treatment; evidence is limited.
Documented risks and interactions (2)
- Gut conversion to TMAO. Gut bacteria turn dietary carnitine into TMAO, which promoted artery disease in mice; meat eaters made far more TMAO than vegans after a carnitine dose.
- Interaction with thyroid medicine. In a 6-month trial in women taking thyroid hormone, L-carnitine reduced hyperthyroid-type symptoms.
Overview
Carnitine is made in the body from two amino acids, lysine and methionine. [1] A 2006 risk assessment calls it a "conditionally essential amino acid-like compound." [2] It is not one of the nine essential amino acids ([3]) and is not built into proteins. Its job is shuttling long-chain fatty acids into the mitochondria (the cell's energy units) so they can be burned. [1] See essential amino acids for the nine.In people who eat meat, about 75% of carnitine comes from the diet and about 25% from the body's own production. [1] In 32 vegans/vegetarians and 40 omnivores, fasting blood carnitine levels were similar. [4] Rare inherited carnitine disorders exist; findings include low blood sugar, heart muscle disease and liver disease. [1] These need medical care, not shop supplements.
Forms
L-carnitine is the form studied for weight and general use. Acetyl-L-carnitine (ALC) is derived from carnitine and has been studied for nerve and brain conditions. [5] Results for one form should not be transferred to the other.Evidence labels used on this page
Promising but limited, mixed, insufficient evidence and marketing claim have their usual meanings. A lab value is not the same as a health outcome.Evidence by use
| Use | What the source found | Label |
|---|---|---|
| Weight (L-carnitine) | A meta-analysis of 37 trials (2,292 people) found body weight fell by 1.21 kg on average; no significant effect on waist circumference or body fat percent. [6] | Promising but limited; small average change |
| Painful nerve damage (ALC) | Four randomized trials in neuropathy from diabetes and HIV treatment showed a pain reduction of 20.2% (relative to baseline) compared with placebo. [7] | Promising but limited; few trials |
| Alzheimer's disease (ALC) | A Cochrane review of 11 trials found no evidence of benefit on cognition or dementia severity and no evidence to recommend routine use. [5] | Insufficient evidence |
| Exercise performance, energy | Proper evidence not found (we searched PubMed and read the ISSN energy drink statement, which said benefits of ingredients beyond caffeine and carbohydrate remain to be determined). [8] | Insufficient evidence |
The TMAO question
Gut bacteria can turn dietary L-carnitine into TMAO, which promoted atherosclerosis in mice; omnivores produced more TMAO than vegans or vegetarians after L-carnitine. [9] In 2,595 people having cardiac evaluation, blood carnitine predicted risk only among those who also had high TMAO. [9] A later study found more than 20-fold higher TMAO generation in omnivores than in vegans/vegetarians after a carnitine dose. [4] These are mechanistic and observational findings; they do not show that supplements cause heart disease in people, but people with heart disease should ask their clinician. See carnitine for heart, fertility and weight claims.Related
Taurine · Beta-alanine · CreatineFrequently asked questions
Is carnitine an amino acid?
It is an amino-acid-like compound made from lysine and methionine, not a protein building block. [1][2]
Do vegetarians need carnitine?
In one study, fasting carnitine levels were similar in vegans/vegetarians and omnivores. [4]
Does carnitine burn fat?
A meta-analysis found about 1.2 kg average weight loss. [6]
What is the difference between L-carnitine and acetyl-L-carnitine?
ALC is derived from carnitine and has been studied for nerve pain and dementia. [5][7]
Does carnitine raise TMAO?
Gut bacteria convert dietary carnitine to TMAO, more in omnivores. [9][4]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Amounts and safety
- Thyroid: in a 6-month trial in 50 women taking thyroid hormone, 2 or 4 g a day of L-carnitine reduced hyperthyroid-type symptoms. [12] That suggests it can work against thyroid medicine; ask your prescriber or pharmacist first, and do not change your medicine.
- Kidney disease, heart disease, seizures, pregnancy, breastfeeding, children, surgery: not described in the sources we read. Talk to a clinician; see medication interactions, supplements before surgery and pregnancy and breastfeeding.
- Products: weight products often mix ingredients; see reading supplement labels and quality testing.
References
- Carnitine Inborn Errors of Metabolism. Molecules 2019 Read 2026-10-23.
- Hathcock and Shao, Risk assessment for carnitine. Regul Toxicol Pharmacol 2006 Read 2026-10-23.
- MedlinePlus Medical Encyclopedia: Amino acids (U.S. National Library of Medicine), review date 21 January 2025 Read 2026-10-23.
- Koeth et al., L-Carnitine in omnivorous diets induces an atherogenic gut microbial pathway in humans. J Clin Invest 2019 Read 2026-10-23.
- Acetyl-L-carnitine for dementia. Cochrane Database Syst Rev 2003 Read 2026-10-23.
- L-carnitine supplementation, weight loss and body composition: meta-analysis of 37 randomized trials. Clin Nutr ESPEN 2020 Read 2026-10-23.
- Acetyl-L-carnitine in painful peripheral neuropathy: a systematic review. J Pain Res 2019 Read 2026-10-23.
- International Society of Sports Nutrition position stand: energy drinks and energy shots. J Int Soc Sports Nutr 2023 Read 2026-10-23.
- Koeth et al., Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med 2013 Read 2026-10-23.
- The Renal Safety of L-Carnitine, L-Arginine, and Glutamine in Athletes and Bodybuilders. J Ren Nutr 2019 Read 2026-10-23.
- Tolerable Upper Intake Level for Individual Amino Acids in Humans: a narrative review. Adv Nutr 2023 Read 2026-10-23.
- L-carnitine in iatrogenic hyperthyroidism: randomized, double-blind, placebo-controlled trial. J Clin Endocrinol Metab 2001 Read 2026-10-23.