L-carnitine is often marketed as an amino acid or even as a vitamin, but both descriptions are misleading. It is better described as an amino-acid-derived, conditionally essential metabolite. The body usually makes enough L-carnitine from lysine and methionine, so most healthy adults do not need extra L-carnitine from supplements.

1. What L-carnitine is:

   • L-carnitine is not a protein-building amino acid. It is derived from amino acids, but it has a different structure and function. It is also not a true vitamin, because the body can usually synthesize enough of it.

2. What L-carnitine does: