L-Carnitine

A small nutrient-like molecule the body makes from lysine and methionine. Prescription levocarnitine (Carnitor) was first FDA-approved in 1985. Despite the catalog's category, it is not a peptide.

Carnitine carries long-chain fatty acids across the inner mitochondrial membrane so they can be burned for energy, and helps clear excess acyl groups from cells. Healthy adults make enough, so deficiency mainly occurs with genetic disorders, dialysis and certain drugs. Unabsorbed oral carnitine is converted by gut bacteria into TMAO.

Placebo-controlled trials in dialysis patients supported the approved IV use for deficiency. For weight, pooled oral trials show about 1.2–1.3 kg more loss than placebo, and no weight-loss trials of injectable forms were found. Exercise research suggests a possible benefit only for high-intensity exercise, and the overall evidence is mixed. A 2013 study found gut bacteria convert carnitine to TMAO, which predicted heart events in cardiac patients and increased atherosclerosis in mice.

The approved label lists nausea, vomiting, body odor and gastritis. Serious risks include seizures (even without a seizure history), anaphylaxis and bronchospasm with IV use, and raised INR with warfarin. A 2022 trial linked L-carnitine to higher total and LDL cholesterol.

FDA-approved prescription drug (Carnitor injection, oral solution and tablets) for carnitine deficiency; also sold as an oral supplement. As the active ingredient of approved drugs, 503A pharmacies may compound it. Not on the WADA list, though WADA's method rules (M2.2) restrict large-volume IV infusions outside hospital settings. Status as of October 2026.