Acetyl-L-carnitine in the body is made from L-carnitine. It can also be converted into L-carnitine. L-carnitine is an amino acid (a building block for proteins) that is produced naturally in the body. It helps to produce energy. Despite being an amino acid, L-carnitine is not used for the production of proteins.

Some people take acetyl-L-carnitine by mouth for various mental disorders such as Alzheimer's disease, age-related memory loss, depression, thinking problems related to alcoholism, thinking problems related to Lyme disease, and very poor liver function. It is also used in Down syndrome, bipolar disorder, poor circulation in the brain after stroke, cataracts, nerve pain due to diabetes, nerve pain due to AIDS or cancer treatment, sciatica, fibromyalgia and facial paralysis.

Acetyl-L-carnitine is used for aging-related fatigue, fatigue associated with a disease called multiple sclerosis, muscle wasting called amyotrophic lateral sclerosis, levels of hyperactivity disorder (ADHD) and attention deficit in children with the genetic fragile-X syndrome. It is taken orally and is used for skin aging, diabetes, high blood pressure and abnormal blood fat levels.

Acetyl-L-carnitine is injected intramuscularly for a pain condition called fibromyalgia and nerve pain that typically affects the hands and feet (peripheral neuropathy). Acetyl-L-carnitine helps the body produce energy. It is important for heart and brain function, muscle movement, and many other body processes.