What is N-acetylcysteine?

N-acetylcysteine, commonly abbreviated as NAC, is the pre-acetylized form of the amino acid cysteine, an amino acid naturally produced by the body. NAC is more stable than cysteine and is also more water soluble and therefore more bioavailable than cysteine. It is a very powerful antioxidant and free radical scavenger and helps protect the body from a variety of harmful agents. NAC is widely available as an oral supplement without a prescription and is believed to have minimal toxicity and side effects.

How does NAC work?

NAC is rapidly metabolized and is thought to have two mechanisms for protecting the body from various types of damage.

  1. NAC is a precursor for the antioxidant glutathione. Glutathione is present in the cells of almost all tissues in the body. It is involved in various normal cellular functions but mainly works to defend the cell from free radicals. Free radicals can damage cellular proteins, lipids, and DNA, potentially causing toxicity or leading to cancer or other diseases. Glutathione directly converts free radicals and other similar, dangerous compounds into harmless compounds that can be removed from the body. The addition of NAC increases the levels of glutathione in cells, boosting the cellular defense against these dangerous compounds.
  2. NAC is also itself an antioxidant because it contains sulfur in the form of sulfhydryl groups. These groups help NAC convert free radicals into less harmful compounds and also directly react with many poisons, trapping them in the gut so they cannot penetrate into the body. Such poisons include heavy metals such as mercury, lead, and cadmium. NAC also helps to remove these poisons from the body by helping certain metabolizing enzymes in the liver.

What are its benefits?

NAC has been the subject of much research to determine its benefits. The most important findings are documented below.

  • NAC is commonly given to patients that have taken an overdose of acetaminophen (Tylenol) or other hazardous compounds including herbicides, carbon tetrachloride, and urethane. NAC is also used to treat patients that have been exposed to heavy metals such as lead and mercury.
  • NAC is also commonly used to treat a variety of bronchoulmonary diseases including cystic fibrosis, chronic bronchitis, asthma, and pneumonia. NAC is mucolytic, meaning it can break up mucus and reduce its viscosity so that it can be coughed up easier. It is thought to do this by cleaving proteins present in the mucus into smaller particles.
  • Studies show NAC may prevent heart disease and may inhibit damage to the heart after a heart attack by removing the free radicals that form. Elevated levels of a lipoprotein called Lp(a) are commonly used as a reliable indicator for a heart attack. Research shows NAC is the most effective compound for lowering these Lp(a) levels, even more effective than a healthy diet and exercise.
  • Since NAC inhibits free radical damage it may also inhibit the occurence and progression of cancer. Various studies have shown that NAC may slow the growth of cancerous cells. NAC also appears to reduce the unpleasant and toxic side effects of some chemotherapy drugs.
  • NAC appears to suppress the replication of certain viruses, most notably HIV. It also attacks various microorganisms such as E. coli.
  • Supplementation of NAC has been shown to improve the immune system, making it better able to fight off disease. Research indicates that taking NAC during the cold and flu season may help ward off these illnesses.

Availability and Side Effects

NAC is widely available as an oral supplement in health food stores in many countries including throughout Europe and the United States. The drug in its intravenous or inhalant form is also available, but a prescription is required. In the United States NAC is available as an inhalant under the name Mucomyst and is commonly used to treat acetaminophen overdose and chronic bronchitis. In Europe it is marketed under the name Fluimucil.

NAC is neither a sedative nor a stimulant and has been shown to have minimal to no side effects at normal doses. No toxicity has been seen at doses of 500 milligrams to 4 grams daily. Larger doses commonly used when treating acetaminophen poisoning have been known to cause nausea, vomiting, and other gastrointestinal symptoms. Even higher doses, generally achieved when NAC is given intravenously, can produce a rash and/or a mild fever as well as more severe toxic effects. There does not appear to be any drug interactions associated with NAC.

Some studies indicate that NAC may actually lower glutathione levels in healthy people, potentially sensitizing them to free radical damage. More research needs to be done, but some doctors and researchers think that healthy people should not take NAC.

As with any drug, even if it does not require a prescription, talk with your doctor before you start taking NAC. See: Does "All Natural" mean "No Side Effects"?