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N-acetyl cysteine (NAC) comes from the amino acid L-cysteine. Amino acids are building blocks of proteins. NAC has many uses and is an FDA approved drug.

N-acetyl cysteine is an antioxidant that might play a role in preventing cancer. As a drug, it's used by healthcare providers to treat acetaminophen (Tylenol) poisoning. It works by binding the poisonous forms of acetaminophen that are formed in the liver.

People commonly use N-acetyl cysteine for cough and other lung conditions. It is also used for flu, dry eye, and many other conditions, but there is no good scientific evidence to support many of these uses. There is also no good evidence to support using N-acetyl cysteine for COVID-19.

Although many dietary supplement products contain N-acetyl cysteine, the US FDA states that it's illegal for dietary supplements to contain N-acetyl cysteine since it's technically an approved drug. Prescription N-acetyl cysteine products are available under the guidance of a healthcare provider.

Natural Medicines rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.
No data available.
  • Angina.  Oral or intravenous N-acetyl cysteine may reduce nitroglycerin tolerance in patients with angina. However, some studies suggest that N-acetyl cysteine might increase the risk for severe headaches and hypotension when used with intravenous or transdermal nitroglycerin.
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  • Autism spectrum disorder.  Oral N-acetyl cysteine may improve irritability, but not other symptoms, associated with autism spectrum disorder.
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  • Bronchitis.  Via inhalation, N-acetyl cysteine is FDA-approved for managing acute episodes of bronchitis. Oral N-acetyl cysteine may help to reduce the occurrence of acute exacerbations of chronic bronchitis when used for 3-36 months.
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  • Chronic obstructive pulmonary disease (COPD).  Taking N-acetyl cysteine orally seems to decrease the exacerbation rate and improve symptoms in patients with moderate to severe COPD, particularly those who are not taking inhaled corticosteroids. Also, taking N-acetyl cysteine along with standard therapy appears to improve recovery in patients hospitalized due to an acute exacerbation.
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  • Contrast induced nephropathy.  Oral or intravenous administration of N-acetyl cysteine seems to prevent contrast induced nephropathy in patients with kidney dysfunction. However, it is not beneficial in those with normal kidney function or diabetes.
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  • Hyperhomocysteinemia.  Oral N-acetyl cysteine seems to reduce homocysteine levels.
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  • Hyperlipidemia.  Oral N-acetyl cysteine seems to reduce lipoprotein(a) levels.
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  • Ifosfamide (Ifex) toxicity.  Oral N-acetyl cysteine may be beneficial for reducing ifosfamide toxicity, although it does not appear to be as effective as mesna.
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  • Influenza.  Oral N-acetyl cysteine may reduce the risk for symptomatic influenza.
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  • Kidney failure.  Oral N-acetyl cysteine may reduce the risk for cardiovascular events in patients with kidney failure.
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  • Myocardial infarction (MI).  Intravenous N-acetyl cysteine, along with standard therapy, seems to improve outcomes in patients with MI. Oral N-acetyl cysteine has not been evaluated for this use.
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  • Head and neck cancer.  Oral N-acetyl cysteine does not seem to reduce mortality, improve event-free survival, or prevent additional tumors in patients with head and neck cancer.
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  • Lung cancer.  Oral N-acetyl cysteine does not seem to reduce mortality, improve event-free survival, or prevent additional tumors in patients with lung cancer.
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  • Multisystem organ failure.  Administering intravenous N-acetyl cysteine might increase the risk of mortality due to multisystem organ failure. Oral N-acetyl cysteine has not been evaluated for this use.
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No data available.
No data available.

When taken by mouth: N-acetyl cysteine is likely safe for most adults. N-acetyl cysteine is an FDA-approved prescription drug. It can cause side effects such as dry mouth, nausea, vomiting, and diarrhea. It has an unpleasant odor that some people find hard to tolerate.

When inhaled: N-acetyl cysteine is likely safe for most adults, when used as a prescription medication. It can cause swelling in the mouth, runny nose, drowsiness, clamminess, and chest tightness.

Special Precautions & Warnings:

Pregnancy: N-acetyl cysteine is possibly safe when taken by mouth or inhaled during pregnancy. N-acetyl cysteine crosses the placenta, but there is no evidence that it harms the unborn child. But N-acetyl cysteine should only be used when medically needed.

Breast-feeding: There isn't enough reliable information to know if N-acetyl cysteine is safe to use during breast-feeding. Stay on the safe side and avoid use.

Children: N-acetyl cysteine is likely safe when taken by mouth in doses of 900-2700 mg daily for up to 12 weeks.

Allergy: Don't use N-acetyl cysteine if you are allergic to acetyl cysteine.

Asthma: N-acetyl cysteine might cause bronchospasm in people with asthma if inhaled or taken by mouth. If you take N-acetyl cysteine and have asthma, you should be monitored by your healthcare provider.

Bleeding disorder. N-acetyl cysteine might slow blood clotting. N-acetyl cysteine might increase the risk of bruising and bleeding in people with bleeding disorders.

Surgery. N-acetyl cysteine might slow blood clotting. This might increase the risk of bleeding during and after surgery. Stop taking N-acetyl cysteine at least 2 weeks before a scheduled surgery.

Activated charcoal

Interaction Rating=Moderate Be cautious with this combination.

Activated charcoal is sometimes used to prevent poisoning in people who take too much acetaminophen and other medications. Activated charcoal can bind up these medications in the stomach and prevent them from being absorbed by the body. Taking N-acetyl cysteine at the same time as activated charcoal might decrease how well it works for preventing poisoning.


Interaction Rating=Major Do not take this combination.

Nitroglycerin can dilate blood vessels and increase blood flow. Taking N-acetyl cysteine seems to increase the effects of nitroglycerin. This could cause increased chance of side effects including headache, dizziness, and lightheadedness.

Herbs and supplements that might lower blood pressure: N-acetyl cysteine might lower blood pressure. Taking it with other supplements that have the same effect might cause blood pressure to drop too much. Examples of supplements with this effect include andrographis, casein peptides, L-arginine, niacin, and stinging nettle.
Herbs and supplements that might slow blood clotting: N-acetyl cysteine might slow blood clotting and increase the risk of bleeding. Taking it with other supplements with similar effects might increase the risk of bleeding in some people. Examples of supplements with this effect include garlic, ginger, ginkgo, nattokinase, and Panax ginseng.

There are no known interactions with foods.

N-acetyl cysteine is an FDA approved prescription drug. It can be taken in various ways, including by mouth, by IV, and by inhalation. It is most commonly taken by mouth in doses of 600-1200 mg daily. Speak with a healthcare provider to find out what type of product and dose might be best for a specific condition.

N-acetyl cysteine is also available in many dietary supplements. But according to the FDA, using N-acetyl cysteine in supplements is illegal because it is an approved drug. Supplement products should not be used in place of prescription products.

Acetyl Cysteine, Acétyl Cystéine, Acetylcysteine, Acétylcystéine, Chlorhydrate de Cystéine, Cysteine, Cystéine, Cysteine Hydrochloride, Cystine, Hydrochlorure de Cystéine, L-Cysteine, L-Cystéine, L-Cysteine HCl, L-Cystéine HCl, NAC, N-Acetil Cisteína, N-Acetyl-B-Cysteine, N-Acétyl Cystéine, N-Acetyl-L-Cysteine, N-Acétyl-L-Cystéine, N-Acetylcysteine, N-Acétylcystéine.

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