L-Carnitine

L-carnitine is a compound synthesised in the body from the amino acids lysine and methionine and also obtained from the diet (mainly red meat). Its core physiological job is to transport long-chain fatty acids across the inner mitochondrial membrane so they can be oxidised for energy. Because of that role it is marketed for fat loss, energy, and exercise recovery, and is frequently offered as an intramuscular or intravenous "lipotropic" injection. It is important to separate two contexts. As the prescription drug levocarnitine (Carnitor), L-carnitine is FDA-approved and well-evidenced for primary and secondary carnitine deficiency, including in dialysis patients. As a performance/aesthetic supplement in people who are not deficient, the evidence is far weaker and inconsistent — roughly two decades of athletic-performance studies have not produced convincing, repeatable benefits for body composition or weight loss in healthy individuals. Material sold for research/injection outside the approved drug supply is unregulated, and the "fat-burning injection" marketing around it outpaces the human data. This entry summarises the science for reference only; it is not medical advice and does not endorse human use.