1–3 g/day in divided doses. For sport the L-tartrate is used; other forms (propionyl, acetyl) have different uses.
The L-tartrate may reduce muscle damage and soreness after exercise.
View the study (RCT) →Small effect on weight, of doubtful clinical relevance.
View the study (meta-analysis) →Some data of benefit in angina, but the evidence is weak.
⏱ 2 min read
L-carnitine is a compound that the body synthesizes from the amino acids lysine and methionine, and whose main function is to transport long-chain fatty acids into the mitochondria so that they serve as fuel for ATP production, which makes it a key piece of muscle and cardiac energy metabolism even though it is not an essential amino acid in the strict sense, because the healthy body can make what it needs.
Clinical carnitine deficiency is rare and usually appears only in specific conditions such as certain genetic diseases, prolonged renal dialysis, or chronic use of some anticonvulsants; in healthy people on a normal omnivorous diet, dietary intake from red meat and dairy covers needs without problems, which has fueled a constant debate about the real role of supplementation in people who already have adequate plasma levels.
The commercial promise of L-carnitine as a fat burner has historically been exaggerated relative to what the clinical evidence shows: the available meta-analyses find modest effects on weight loss (on the order of 1.3 kilos in people with overweight after months of use) and no robust benefit on fat oxidation during exercise in people with normal muscle carnitine levels.
Where there is more interesting evidence is in recovery after intense exertion: L-carnitine, especially in its L-tartrate form, reduces markers of muscle damage and perceived pain in the 24 to 72 hours after demanding workouts, with an effect that appears to be related to better availability of muscle carnitine to buffer the metabolic stress of high-intensity exercise.
In heart failure and coronary disease, several trials have shown modest improvements in clinical parameters such as ejection fraction, exercise capacity, and anginal symptoms at doses of 2 to 3 grams per day; this indication has the most robust evidence and is the one that some cardiology guidelines mention as a reasonable adjunct in selected patients, though never as a substitute for standard treatment.
The most controversial debate about L-carnitine comes from the discovery that part of what we ingest is metabolized by gut bacteria into TMAO (trimethylamine N-oxide), a compound that has been associated in observational studies with higher cardiovascular risk; the clinical relevance of this finding remains a matter of discussion and depends heavily on the individual microbiota, dietary pattern, and cumulative dose.
For general use, the doses studied range from 500 milligrams to 3 grams per day, divided into two or three doses with meals; the L-carnitine L-tartrate form is the most widely used in sports because of its better bioavailability and the specific evidence on post-exercise recovery, whereas the propionyl-L-carnitine and acetyl-L-carnitine forms have different indications (cardiovascular for the former, neurological for the latter).
L-carnitine is generally well tolerated; the most frequent adverse effects are digestive discomfort and a characteristic fishy body odor due to intestinal production of trimethylamine; people with advanced kidney disease should consult a doctor first because clearance may be compromised, and the TMAO question should be put into context before deciding whether prolonged use is worthwhile in people with additional cardiovascular risk factors.
Information, not medical advice. Scientific evidence reflects the quality of the studies.