Although not as exactly as much of an amino acid (more traditionally it is related to B vitamins) as the others, carnitine is usually considered linked to them due to a similar chemical structure. As opposed to “true” amino acids which are used for protein synthesis and/or neurotransmitters, carnitine’s main function is to aid transport of long-chain fatty acids that are burned in the cells to provide energy. This one of the main sources of energy for the muscles. Carnitine therefore increases the use of fat as an energy source. Effectively limiting fatty buildup (especially in the heart, liver, and skeletal muscles).
Carnitine may be effective in the treatment of CFS (chronic fatigue syndrome), due to two reasons; 1. Those with CFS have shown decreased carnitine levels 2. A disturbance in the function of the mitochondria (area of the cell that carnitine transports energy to) may be a factor in fatigue.
According to The American Journal of Cardiology has one study that showed a carnitine derivative, proprionyl-L-carnitine, easing the severe pain of intermittent claudication, a condition in which blocked arteries in the thighs decrease the supply of blood and oxygen to leg muscles causing pain, mainly during physical activity.

Carnitine can:
Lower blood triglyceride levels
Improve muscle stength in those afflicted with neuromuscular disorders
Improve the mobility of sperm
Aid in weight loss
May be useful in treating Alzheimers

The human body can only manufacture carnitine if enough iron, vitamin B1 (thiamine, vitamin B6 (pyridoxine) and the amino acids methionine and lysine are present. Adequate levels of vitamin C also plays a role in the synthesis of carnitine.

ALC (acetyl-L-carnitine)
ALC is a derivative of carnitine and is produced in the body naturally. ALC has recently become the most researched compound due to the anti-aging properties it possesses, especially on the brain and nervous system. Many studies have shown that daily ALC supplementation significantly slows Alzheimers disease, meaning less deterioration of the memory, language, and attention. ALC may also be used to treat other cognitive disorders, and depression.
Those are not the only benefits of ALC however, ALC also helps to protect against oxidative stress, stimulate the antioxidant activity of some enzymes, sow cerebral aging, prevent nerve disease associated with diabetes, increase the performance enhancing effects of branched-chain amino acids, and much more.
No toxic or serious side effects have been found to be linked to ALC