N-Acetyl-L-Cysteine

Cysteine is an amino acid that can be found throughout the body. N-acetyl-L-cysteine (NAC), a modified form of cysteine, has been shown to increase levels of the antioxidant glutathione. Antioxidants such as glutathione can reduce cell damage, speed recovery from injury and aid muscle growth.
NAC is a popular supplement with a wide variety of uses. Because it reduces muscle damage and strengthens the immune system, NAC is used extensively by endurance athletes, such as long-distance runners, cyclists and triathletes. Many athletes also include NAC in their diet when they are in the early stages of recovering from an injury. The anabolic effect of NAC on muscle tissue also makes it popular with athletes wanting to gain lean muscle size and strength, including bodybuilders, rugby players, and sprinters.
Just one bout of treadmill running can increase free radical levels by more than 300%. Free radicals are believed to contribute to the aging process as well as the development of a number of health problems including heart disease and cancer. Antioxidants such as glutathione can neutralize free radicals and may reduce or even help prevent some of the damage they cause.
By protecting against free radical damage, NAC is also thought to accelerate muscle growth. In one study, NAC was shown to completely prevent the muscle loss that normally occurs as part of the aging process. NAC has also been shown to dramatically reduce muscle fatigue during exercise. This is one reason why it's popular with bodybuilders and strength athletes seeking to gain muscle size and weight.
Glutathione is also known to aid in the transport of nutrients to various immune cells, and to protect cell membranes. While glutathione is available as a dietary supplement, absorption is notoriously low, and NAC is thought to be a better source method of boosting cellular glutathione levels.
Endurance athletes (such as long-distance runners, cyclists or triathletes) report that NAC helps them tolerate large volumes of training while remaining free of illness. NAC is also considered to be one of the safest and most well-studied antioxidant supplements available. For more than three decades, NAC has been used as a "mucus dissolving" agent to help break up the thick mucus often present in people suffering from chronic respiratory ailments.
NAC has a wide variety of uses, and the amount used depends to a large extent on the goals of the individual. For recovery from injury, most experts recommend 1,000-1500 milligrams of NAC daily, consumed in 3-4 divided doses. To gain muscle size and strength, most bodybuilders use up to 200 milligrams of NAC daily in 1-3 divided doses.
NAC is highly effective when consumed alone. However, combining it with Whey protein and/or Glutamine is very popular with both endurance athletes and bodybuilders alike. The healing properties of NAC may also be enhanced by combining it with Turmeric.