Clayton's Health Facts: N-Acetyl Cysteine.

Clayton South, SPN (ISSA), is a recognized expert in the bodybuilding / fitness industry with over 150 bodybuilding, fitness and nutrition publications to his credit.

What Is It? And Where Does It Come From?

N-Acetyl Cysteine (C5H9NO3S) is an L-Cysteine derivative that is more stable than L-Cysteine. While L-Cysteine is readily found in the diet - mostly from lean meat sources, NAC is not present in the diet and must be obtained via dietary supplementation.

N-Acetyl Cysteine is also known as NAC and Acetylcysteine.

As an L-Cysteine derivative, NAC is more water soluble, and therefore more bioavailable than regular L-Cysteine.

What Does It Do? And What Scientific Studies Give Evidence To Support This?

Research has established that NAC exerts powerful antioxidant effects.1 In this role, NAC scavenges the body for, and neutralizes, harmful free radicals that can cause oxidative damage to muscle tissue, bodily organs, and DNA.

As an antioxidant, it may reduce oxidative stress, thereby preventing the onset of some cancers and possibly slowing the aging process. NAC may also boost immune system function by acting as a glutathione precursor.

What Is Glutathione?

One of the body's most powerful intracellular antioxidant enzymes and detoxifying agents. Cysteine (along with glycine and glutamate) is an amino acid and precursor of glutathione. NAC enhances the production of glutathione.

In addition, glutathione is believed to protect other antioxidants (among them, vitamins C and E), prolonging and enhancing their effectiveness. It also acts directly against certain carcinogenic substances by binding to these toxins and eliminating them through urine or bile.

In addition to protecting the body from oxidative damage resulting from normal metabolism and environmental toxins, NAC has shown positive effects on liver function, protecting the liver from heavy metals like lead and mercury, and protecting against damage resulting from acetaminophen use.

In fact, the effects of NAC on the liver are so powerful that it is now commonly used to help treat liver failure resulting from drug use and hepatitis.2

NAC exerts many other beneficial effects on the body, including the ability to break down mucus structures, lessen the symptoms of chronic bronchitis3, the ability to protect the colon from damage resulting from polyp formation4, and the ability to stop the replication of several HIV strains.

Who Needs It? And What Are Some Symptoms Of Deficiency?

NAC is not an essential nutrient and no symptoms of deficiency exist.

Healthy adults can benefit from using NAC as a dietary supplement.

Naturally training athletes can benefit from supplemental use of NAC because of its ability to protect the immune system from harmful oxidants that result from environmental pollution, regular metabolic functions and intense exercise.

Frequently, the use of anabolic substances can elevate liver enzyme levels in excess of normal levels. Liver enzyme elevation is a sign of liver inflammation and, in some cases, this inflammation can lead to induced hepatitis.

Heavy steroid users need to use NAC for post-cycle therapy (along with other dietary supplements) to reduce liver enzyme levels and restore proper liver function.

NAC supplementation may help support proper immune system function by reducing the impact of prescription drugs on immune function and overall health. NAC supplementation, therefore, may be warranted if you take prescription medications.

Because NAC demonstrates antioxidant effects, can break down mucus structures, and is clinically proven to reduce the symptoms of acute bronchitis, it may have beneficial effects for persons with asthma or acute bronchitis.

It is possible that NAC can protect the lungs from oxidative damage, though further research is needed to test this hypothesis.

Finally, NAC can prevent colon polyp formation, and this is significant because processed foods - which are consumed in high amounts by most people—contribute to these formations and these formations may result in colon cancer and a loss of bowel control.

How Much Should Be Taken? And Are There Any Side Effects?

Adhere to label directions.

Side effects that can occur with NAC use at high doses include nausea, headache, vomiting, dizziness, and abdominal pain. Research has shown that NAC can function as an oxidant if taken at high doses.5

NAC may lead to the excretion of zinc and copper—metals required for proper hormone function, so be sure to supplement with these minerals if you use NAC.6

NAC tolerance is generally excellent in most users and NAC is not known to be contraindicated with any dietary supplements or prescription drug products.


  1. Van Schayck CP, Dekhuijzen PNR, Gorgels WJMJ, et al. Are anti-oxidant and anti-inflammatory treatments effective in different subgroups of COPD? A hypothesis. Respir Med 1998;92:1259-64.
  2. Ben-Ari Z, Vaknin H, Tur-Kaspa R. N-acetylcysteine in acute hepatic failure (non-paracetamol-induced). Hepatogastroenterology, 2000;47:786-9.
  3. Multicenter Study Group. Long-term oral acetylcysteine in chronic bronchitis. A double-blind controlled study. Eur J Respir Dis 1980;61:111:93-108.
  4. 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;147:109-14.
  5. Kleinveld HA, Demacker PNM, Stalenhoef AFH. Failure of N-acetylcysteine to reduce low-density lipoprotein oxidizability in healthy subjects. Eur J Clin Pharmacol 1992;43:639-42.
  6. Brumas V, Hacht B, Filella M, Berthon G. Can N-acetyl-L-cysteine affect zinc metabolism when used as a paracetamol antidote? Agents Actions, 1992;36:278-88.