Acetyl-?-carnitine is an active form of carnitine that is synthesized in the body or obtained through dietary sources, in particular red meats. For this reason, many people who eat a vegetarian diet may have a relative deficiency. Acetyl-?-carnitine has the ability to cross the blood-brain barrier and neural cell membranes, and therefore can be helpful in conditions affecting the nervous system. Acetyl-?-carnitine has been studied for its ability to improve mental fatigue associated with fibromyalgia and chronic fatigue syndrome. Unlike the ?-carnitine form, it has been suggested to promote cognition.