Herbs & Supplements:
N-Acetyl Cysteine (NAC)
Principal Proposed Uses
•
Chronic Bronchitis, Angina Pectoris (in Combination with Conventional Treatment)
Other Proposed Uses
•
Acute Respiratory Distress Syndrome, Protection Against Kidney Damage Caused by Contrast Agents , Chronic Blepharitis, Sjogren’s Syndrome, Alzheimer's Disease, Liver Disease, Colon Cancer Prevention, HIV Support, Chemotherapy Support, Parkinson's Disease
N-acetyl cysteine (NAC) is a specially modified form of the dietary amino acid cysteine. When taken orally, NAC is thought to help the body make the important antioxidant enzyme glutathione. It has shown promise for a number of conditions, especially chronic bronchitis.
Sources
There is no daily requirement for NAC, and it is not found in food.
Therapeutic Dosages
Optimal levels of NAC have not been determined. The amount used in studies has varied from 250 to 1,500 mg daily.
It has been suggested that NAC may increase excretion of trace minerals; while some evidence suggests that this effect is too minimal to make a real difference.47 Prudence suggests that individuals taking NAC for an extended period of time should also consider taking a standard multivitamin/multimineral supplement.
Therapeutic Uses
Evidence suggests that regular use of NAC is helpful for individuals with chronic bronchitis, a condition commonly associated with smoking and emphysema.1–9
Mixed evidence suggests that NAC may be helpful for people who take the drug nitroglycerin for angina (the chest pain associated with heart disease).10–15 However, severe headaches may develop as a side effect.
NAC may be helpful in a life-threatening condition called acute respiratory distress syndrome.16Very high dosages of NAC are used in hospitals as a conventional treatment for acetaminophen poisoning.
Note: Do not attempt to self-treat angina, acute respiratory distress syndrome, or acetaminophen poisoning! Medical supervision is absolutely essential because of the very real risk of death in these conditions.
In order to get more information from certain types of x rays, radiologists often administer substances called "contrast agents." Unfortunately, contrast agents can damage the kidney. Growing evidence indicates that NAC can help protect the kidney from such damage.17,48
Some research has also suggested that NAC may be effective has also shown promise as a treatment for Sjogren’s syndrome (a disease that causes dry eyes, among other symptoms), chronic blepharitis (ongoing infections of the eyelid), Alzheimer’s disease and various forms of severe liver disease.49-51 Other evidence hints that NAC might help offset the carcinogenic effects of smoking and reduce colon cancer risk.18,52
NAC has been proposed as supportive therapy for HIV, but despite some promising results, overall the evidence is inconsistent at best. 23,24,41-44
NAC is also sometimes recommended for helping chemotherapy work better as well as reducing its side effects. It has also been suggested as a treatment for Parkinson's disease. However, there is no meaningful scientific evidence that it is effective for these purposes.
One double-blind trial did not find NAC effective for head and neck or lung cancer.25
What Is the Scientific Evidence for N-Acetyl Cysteine (NAC)?
Chronic Bronchitis
Individuals who have smoked cigarettes for many years eventually develop deterioration in their lungs leading to various symptoms, including chronic production of thick mucus. This so-called chronic bronchitis tends to flare up periodically into severe acute attacks possibly requiring hospitalization.
Regular use of NAC may diminish the number of these attacks. A review and meta-analysis selected eight double-blind placebo-controlled trials of NAC for chronic bronchitis.26–34 The results of these studies, involving a total of about 1,400 individuals, suggest that NAC taken daily at a dose of 400 to 1,200 mg can reduce the number of acute attacks of severe bronchitis. It is not clear how NAC works; the old concept that it acts by thinning mucus may not be correct.
Angina Pectoris
Angina pectoris is a squeezing feeling in the chest caused by inadequate blood supply to the heart. It can be a precursor of heart attacks. People with angina often use the drug nitroglycerin to relieve symptoms. One 4-month double-blind placebo-controlled study of 200 individuals with heart disease found that the combination of nitroglycerin and NAC significantly reduced the incidence of heart attacks and other severe heart problems.35 NAC alone and nitroglycerin alone were not as effective. The only problem was that the combination of nitroglycerin and NAC caused severe headaches in many participants. This effect has been seen in other studies as well.36
NAC may also help in cases of nitroglycerin tolerance, a condition in which the drug becomes less effective over time. In a small double-blind study of 32 people with angina, tolerance developed in 15 of 16 individuals who took nitroglycerin only, but in just 5 of 16 individuals who took nitroglycerin plus 2 g of NAC daily.37 However, other studies have found no benefit.38
Acute Respiratory Distress Syndrome
A double-blind placebo-controlled clinical trial compared the effectiveness of NAC, Procysteine (a synthetic cysteine building-block drug), and placebo in 46 people with acute respiratory distress syndrome.39 This catastrophic lung condition can be caused when an unconscious person inhales his or her own vomit. Both NAC and Procysteine reduced the severity of the condition in some people (as compared with placebo). However, overall it did not reduce the number of deaths.
Colon Cancer Prevention
A preliminary double-blind placebo-controlled study of NAC enrolled 62 individuals, each of whom had had a polyp removed from the colon.40 The abnormal growth of polyps is closely associated with the development of colon cancer. In this study, the potential anticancer benefits of NAC treatment were evaluated by taking a biopsy of the rectum. Individuals taking NAC at 800 mg daily for 12 weeks showed more normal cells in the biopsied tissue as compared to those in the placebo group.
Safety Issues
NAC appears to be a very safe supplement when taken alone, although one study in rats suggests that 60 to 100 times the normal dose can cause liver injury.45
As mentioned above, the combination of nitroglycerin and NAC causes severe headaches. Safety in young children, women who are pregnant or nursing, and individuals with severe liver or kidney disease has not been established.
Interactions You Should Know About
If you are taking nitroglycerin, NAC may cause severe headaches.
View References
Last reviewed September 2002 by Medical Review Board
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