Acetyl L-carnitine plays many roles in the body. It has the critical function of preventing the mitochondrial "energy furnaces" in our body from being shut down when the system backs up. Also, without sufficient carnitine, the body cannot burn fat (and, in fact, makes excess fat), resulting in large weight gain.
L-carnitine is a naturally occurring nutrient found in animal flesh (which is why meat eaters are called "Carni-vores"). Carnitine can also be synthesized in the body.
Helpful for energy production, acetyl L-carnitine is even more important to take if you have mitral valve prolapse, Neurologic pain or disorders, and/or elevated blood triglycerides. It may also help with weight loss.
The "acetyl" form of carnitine (acetyl L-carnitine) gets into cells where it is needed much more effectively than plain carnitine.
Though many studies use 3,000 mg a day, 1,000-2,000 mg a day for 3-4 months followed by 500-1,000 mg a day may well be optimal.