Cold and flu fighter. The landmark 1997 NAC and flu study published in the European Respiratory Journal, involved 262 elderly patients who received 600 milligrams of NAC or placebos twice daily over the cold and flu season. Few of the subjects taking NAC developed flu symptoms, even though blood tests confirmed they were infected. Those who did develop symptoms suffered only mildly.

Control of other infections. A study of AIDS patients found that high doses of NAC—several grams daily—significantly lengthened life expectancy. The researchers also noted that high blood levels of glutathione were better than immune-cell numbers in predicting survival (Proceedings of the National Academy of Sciences, 1997). Combined with the flu study, these findings point to NAC's ability to help fight a wide range of viral infections.

Liver detox. In acetaminophen overdose, the liver's levels of glutathione are completely depleted, quickly leading to liver failure. NAC can help restore liver glutathione levels, and should be part of any liver detox program, at about only 500 milligrams daily.

Polycystic ovary syndrome. About 10 percent of women of childbearing age have PCOS, a condition characterized by enlarged cystic ovaries, high levels of male hormones, infertility and prediabetic insulin resistance. A 2004 study in the International Journal of Gynecology and Obstetrics found that NAC supplements significantly reduced testosterone and insulin levels and improved glucose tolerance.

Cocaine addiction. Several recent clinical studies have shown that high doses of NAC (1,200 to 3,600 milligrams daily) may help with behavioral disorders and cocaine addiction (Psychopharmacology, 2006, Journal of Clinical Psychiatry, 2004).

High-quality NAC supplements will have a rotten-egg smell because of their high sulfur content.

NAC is extraordinarily safe. Do not substitute pure L-cysteine, which can be neurotoxic in high doses.