http://www.futurescience.com/nac.html
I've talked about NAC to half a dozen members or so over the last few years. I currently take this chemical every other year, for six months at a time. This is an exerpt.
N-Acetyl-Cysteine (NAC) is an important life extension supplement. It is an acetylated form of the amino acid cysteine. NAC is a potent antioxidant.
NAC is used by the body to make glutathione peroxidase, one of the body's most important naturally occurring antioxidants. NAC raises glutathione levels better than taking supplemental glutathione.
NAC is an excellent mucolytic agent. It keeps the membranes of the respiratory system moist, thereby lessening the irritation of dry air, dust, and pollutants. It also helps the immune system to do its job properly in the respiratory tract. NAC is available as a prescription drug for this purpose, but you can buy NAC in a health food store for far less money.
The cysteine in NAC is an essential component in hair and nails. Some people find that it enhances nail growth and makes nails less brittle.
NAC helps to prevent damage by aldehydes, which are breakdown products of alcohol [and of the small, but potentially harmful, amounts of methanol produced by aspartame (Nutrasweet)].
NAC can help to prevent damage to the liver caused from overuse of acetaminophen (Tylenol). NAC is the standard treatment for acetaminophen overdose. It is prudent to take NAC whenever one uses acetaminophen. (Acetaminophen is known as paracetamol outside the United States.)
NAC is a chelator of heavy metals. In other words, NAC binds to toxic heavy metals such as mercury and lead, and removes them from the body. This is a slow process, but most chelating agents, such as EDTA, must be given intravenously. NAC is one of the most effective oral chelating agents. Taken regularly over a period of time, NAC will remove many toxic heavy metals from the body. Toxic metals can accumulate in the body over time from many sources such as drinking water and possibly even from tooth fillings made of silver-mercury amalgam. These heavy metals catalyze free-radical reactions. (Free-radical reactions are the dangerous chemical reactions that are prevented by antioxidants.) When certain heavy metals catalyze these free-radical reactions, they initiate free-radical reactions without being used up during the reaction. So these heavy metals continue to cause free radical damage as long as they are present in the body.
It is recommended that persons taking the amino acid cysteine take at least three times as much vitamin C as cysteine to prevent the possibility of oxidized cysteine forming kidney stones. N-Acetyl-Cysteine is much more stable and resistant to being oxidized to an insoluble form. Nevertheless, it is wise to take at least as much vitamin C as N-Acetyl-Cysteine. (Diabetics should consult their physician before using N-Acetyl-Cysteine, since it may have an insulin-blocking effect.)
Typical supplemental doses of N-Acetyl-Cysteine are 500-1500 mg. per day.