L-carnitine is an amino acid that is produced in the body. L-carnitine helps the body turn fat into energy. The body can convert L-carnitine to other amino acids called acetyl-L-carnitine and propionyl-L-carnitine. But, no one knows whether the benefits of these other carnitines are the same. Until more is known, don't switch one form of carnitine for another.
L-carnitine is taken by mouth to increase L-carnitine levels in people whose natural level of L-carnitine is too low. Some people also use L-carnitine for conditions of the heart and blood vessels, overactive thyroid, inability to become pregnant within a year of trying to conceive (infertility), serious kidney disease, and many other conditions, but there is no good scientific evidence to support these uses.
L-carnitine helps the body produce energy. It is important for heart and brain function, muscle movement, and many other body processes.