What to Know About NAC Supplements

NAC is both a medication and a supplement. As a medication it has proven benefits for preventing liver damage from acetaminophen poisoning. As a supplement it has many possible benefits, but no proven benefits.

NAC supplements that may have benefits

Don’t ignore the powerful NAC benefits to be had from this form of the amino acid L-cysteine.

NAC, the acronym for N-acetylcysteine, is used as both a prescription medication and an over-the-counter supplement. As a medication, NAC has proven benefits for preventing liver damage caused by an overdose of acetaminophen (Tylenol). It is also used as a medication to break up mucous in the lungs, although the evidence for this benefit is not as strong. [1,2]

By far, the most common use of NAC is as a supplement. NAC is a naturally occurring amino acid. In the body, NAC is turned into glutathione, a powerful antioxidant. NAC and other antioxidants are popular supplements because of their potential to prevent cell damage. [2,3]

When you exercise, convert food into energy, or you are exposed to sunlight or toxins, free radicals are produced. Free radicals are unstable molecules that can cause cell damage. This damage is called oxidative stress. Antioxidants prevent oxidative stress. [4]

Possible Benefits of Antioxidant Supplements

According to the National Center for Complementary and Integrative Health, there is good evidence for benefits from antioxidants in fruits and vegetables. The evidence of antioxidant benefits from supplements is not as good. In well controlled studies of over 100,000 people, no consistent evidence was found that antioxidant supplements prevent chronic disease, cancer, or heart disease. [4]

Who Should Take NAC

NAC supplements are popular and are taken for many reasons. The benefits have been studied in cell and animal studies, and less frequently in human studies. Here are the most common uses:

  • Depression, though studies on NAC for depression have mixed results. There is no evidence that NAC can be used as a treatment for depression. [2]
  • Cancer; however, there is no evidence that NAC prevents cancer, but some evidence that it may reduce side effects from cancer treatments. [2]
  • Substance abuse. Some human studies have found that NAC may reduce drug abuse, but other studies have not found any benefits. [2]
  • Athletic performance. Some human studies have found benefits for NAC to improve exercise and athletic performance. [3]
  • Anti-aging. Claims for these benefits are based mainly on animal studies showing improvement in age related loss of brain functions, called neurodegeneration. In human studies, NAC has shown some improvement in brain function (cognition) and in chronic fatigue syndrome. [3]

How to take NAC

NAC is available in supplements. There is no established dose. In studies, dose ranges varied widely from just over one gram to 20 grams. Since the Food and Drug Administration does not regulate supplements, and the dose changes with how the supplements are made, there is no way to know the best dose. The best option is to follow the directions on the supplement label. [3]

Risks of Taking NAC Supplements

NAC may interfere with certain medications, including nitroglycerin (a heart medicine) and carbamazepine (an anti-seizure medication). Side effects may include:

  • Nausea
  • Vomiting
  • Diarrhea
  • Fatigue
  • Eye irritation
  • Skin rash [1,2]

Less common side effects are headache, low blood pressure, allergy, or asthma attack. [2] Although NAC is usually safe in most supplement doses, higher doses for use as an athletic enhancer, or long-term dosing have not been studied. Because antioxidants may protect cancer cells as well as normal cells, high-dose antioxidants have been linked to lung cancer in smokers and prostate cancer. [3]

Memorial Sloan Kettering Cancer Center says that some cancer drugs may create free radicals to kill cancer cells. Taking NAC may interfere with these drugs. If you are taking a chemotherapy drug for cancer, check with your doctor before taking NAC. [2]

The Bottom Line on NAC

According to a 2019 review of NAC supplement benefits published in the journal Antioxidants, the most promising benefits so far in humans are for neurodegeneration. Future studies in humans will probably tell us more about benefits, safety, and the most effective doses for various uses. [3] For now, there is not enough evidence to recommend NAC as a treatment or prevention for any condition. Talk to your doctor if you would like to try this or any other antioxidant supplement. [2,3,4]


  1. Mayo Clinic, Acetylcysteine (Inhalation Route) Description and Brand Names – Mayo Clinic
  2. Memorial Sloan Kettering Cancer Center, N-Acetylcysteine | Memorial Sloan Kettering Cancer Center (mskcc.org)
  3. Antioxidants, Medical and Dietary Uses of N-Acetylcysteine (nih.gov)
  4. National Center for Complementary and Integrative Health, Antioxidants: In Depth, Antioxidants: In Depth | NCCIH (nih.gov)

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Chris Iliades, MD

Dr. Chris Iliades is board-certified in Ear, Nose and Throat and Head and Neck Surgery from the American Board of Otolaryngology and Head and Neck Surgery. He holds a medical … Read More

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