Cysteine / N-Acetylcysteine

Cysteine / N-Acetylcysteine (NAC): Overview

N-acetyl cysteine (NAC) is an altered form of the non-essential amino acid cysteine, which is commonly found in food and synthesized by the body.  The oral cysteine that is best tolerated is called N-Acetyl Cysteine.

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Indications are that N-acetyl cysteine is anti-aging; anti-oxidant; a powerful aid in protecting the body from radiation; it deactivates free radicals; is vital for the formation of skin and cell recovery particularly after surgery or cellular damage from burns.  Hair and skin contain cysteine.


Cysteine, the amino acid from which NAC is derived, is found in most high-protein foods.  The food that contains most cysteine is egg yolk.  NAC is not found in the diet.

L-Cysteine is found either by itself or with other amino acids for general amino acid supplementation.  It is also found in formulas designed for detoxification, as it has been in veterinary science for some time.

Function; Why it is Recommended

Cysteine (L- Cysteine) is one of 20 amino acids used by our bodies to make protein molecules.  Cysteine, also known as beta-mercaptoalanine, and the amino acid methionine are the two sulfur-containing amino acids.  Cysteine is a vital component of many proteins in the body, including all of those whose structure is dependent on a disulfide bond (for example, antibodies).

Cysteine has been used for many years in the veterinary sciences as a detoxifying agent.  It has the ability to bind metals such as cadmium and mercury, able to prevent acetaldehyde poisoning (from chronic alcohol or cigarette smoking), and has the ability to increase the activities of both Vitamin B6 and glutathione.

NAC helps the body synthesize glutathione, an important antioxidant.  Cysteine is the rate-limiting amino acid in the production of glutathione.  In other words, if one is low in cysteine, the production of glutathione can not move forward.  Many studies have shown that supplementation of cysteine has led to increased intercellular levels of glutathione.

Deficiencies of NAC have not been defined and may not even exist.  Healthy people do not need to supplement NAC.

The use of N-Acetyl L-Cysteine in medicine is well researched and documented for a variety of conditions.  NAC is a precursor to one of the body's most potent anti-oxidants, glutathione.  It is through this action, that NAC is used for help in liver support, and has even been used to prevent acetaminophen (Tylenol) poisonings.

Probably its best-known use is as a mucolytic.  By breaking the disulfide bonds in the mucus of the intestines and especially the lungs, NAC is able to break down the mucus and make it less viscous.  This is especially important during asthma, bronchitis, and bouts of hay fever.

As an antioxidant, NAC has a number of scavenging activities that benefit many organ systems and is often used in antioxidant supplements.


Optimal levels of supplementation remain unknown, though much of the research uses 250-1,500mg per day.

On This Page

Cysteine / N-Acetylcysteine:

Cysteine / N-Acetylcysteine (NAC) can help with the following:


Cigarette Smoke Damage

NAC is a beneficial nutrient for the lungs both during and after cessation of smoking.


In 2009 it was reported that a 12-week trial with 50 patients indicated that 56% were "much or very much improved" with N-acetylcysteine use compared with only 16% of those taking placebo.


Parkinson's Disease

Both cysteine and NAC increase glutathione levels.


Allergic Rhinitis / Hay Fever

N-acetylcysteine is recommended at 200mg three times per day.


Coronary Disease / Heart Attack

Cysteine is sometimes used to help lessen the risk of coronary artery disease.

Environment / Toxicity

Mercury Toxicity (Amalgam Illness)

The ability of NAC to enhance methylmercury excretion when given orally, its relatively low toxicity, and its wide availability in the clinical setting indicate that it may be an ideal therapeutic agent for use in cases of methylmercury poisoning. [Environ Health Perspectives, 1998, 106(5): pp.267-71]

Earlier concerns over NAC causing mercury to accumulate in the brain and kidneys, as can occur with L-cysteine, now appear to be unfounded.  The initial concerns were opinions only, based on L-cysteine research, not NAC research.  Still, some clinicians feel that symptom worsening occurs with the use of large doses of NAC (over 300mg per day), especially if they already have elevated levels of L-cysteine.  If L-cysteine levels are elevated, cysteine-containing products such as protein powders should be avoided.

Heavy Metal Toxicity

Cysteine acts as a complexing agent by attaching itself to lead and carrying it out of the body.  It is a heavy metal scavenger and liver protector.



Deficiencies of the related amino acid cysteine have been reported in HIV-infected patients.

Lab Values

High Total Cholesterol

Cysteine is sometimes used to improve cholesterol ratios.



COPD (Chronic Obstructive Pulmonary Disease)

NAC helps break down mucus.  Double-blind research has found that NAC supplements improved symptoms and prevented recurrences in people with chronic bronchitis.  NAC may also protect lung tissue through its antioxidant activity.

Tumors, Benign

Colon Polyps

Supplementation with NAC has been shown to reduce the proliferation of certain cells lining the colon and may reduce the risk of colon cancer in people with recurrent polyps in the colon. [Estensen RD, Levy M, Klopp SJ, et al. N-acetylcysteine suppression of the proliferative index in the colon of patients with previous adenomatous colonic polyps. Cancer Lett 1999;147: pp.109-14].

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