N-acetyl cysteine is a modified form of L-cysteine, an amino acid found in many high-protein foods. It doesn't occur naturally in our diets -- our bodies synthesize it from L-cysteine and then convert it into glutathione, an antioxidant.
Uses: NAC is a common treatment for acetaminophen poisoning and is sometimes used for clearing mucous from the lungs. Supplements are taken to protect against harmful agents, such as industrial pollution, radiation, heavy metals and cigarette smoke. They're also taken in hopes of combating the flu and other viruses as well as heart, lung and liver diseases.
Dose: Usually, about 500 milligrams twice a day, though manufacturers suggest doses from 200 to 2,000 milligrams a day. NAC is available in capsules, tablets, powder form and as a solution.
Precautions: N-acetyl cysteine can cause nausea, vomiting, drowsiness, breathing difficulty and headaches.
Research: Human trials and lab studies showing that NAC solution, available by prescription, breaks down mucus in the lungs and can benefit chronic bronchitis sufferers and flu patients. Evidence that supplements in pill or powder form can alleviate symptoms caused by viruses or prevent damage from environmental toxins is much more limited.
Dietary supplement makers are not required by the U.S. government to demonstrate that their products are safe or effective. Ask your health-care provider for advice on selecting a brand.
-- Elena Conis