In the body, acetyl-L-carnitine is made from L-carnitine. It can also be converted to L-carnitine. L-carnitine is an amino acid (a building block for proteins) that is naturally produced in the body. It helps produce energy. Although it is an amino acid, L-carnitine is not used to make proteins.

   Acetyl-L-carnitine is used for a variety of mental disorders including Alzheimer's disease, age-related memory loss, late-life depression, thinking problems related to alcoholism, thinking problems related to Lyme disease, and thinking problems related to very poor liver function (hepatic encephalopathy). It is also used for withdrawal from alcohol, Down syndrome, bipolar disorder, poor circulation in the brain after a stroke, cataracts, nerve pain due to diabetes, nerve pain due to drugs used in the treatment of AIDS or cancer, nerve pain caused by sciatica, fibromyalgia, and facial paralysis. Acetyl-L-carnitine is used for tiredness related to getting older, tiredness related to a disease called multiple sclerosis, a muscle wasting disease called amyotrophic lateral sclerosis, high levels of activity in children with the genetic condition fragile-X syndrome, and attention deficit-hyperactivity disorder (ADHD). It is also used for aging skin.