NAC supplement: what it does and what the evidence shows
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- NAC 600 mg capsules with selenium. Best for: Adults who want the common 600 mg NAC form. See options on Amazon
- NAC without added ingredients. Best for: People who want NAC alone. See options on Amazon
- NAC with glutathione. Best for: Buyers comparing antioxidant combinations. See options on Amazon
What NAC is
MSK's About Herbs database describes NAC as an antioxidant and a precursor to glutathione, one of the body's main antioxidants. It is used as a prescription drug, given by vein or mouth for acetaminophen overdose, and as an inhaled or oral solution to break up mucus in lung disease.
As a supplement, oral NAC capsules are marketed for liver protection and immune support. MSK notes that NAC products can have an unpleasant odor.
How it works. MSK explains that NAC breaks certain chemical bonds in mucus, which is why it thins mucus in lung disease, and that its liver protection may come partly from raising glutathione. That glutathione link is the main reason it is sold as an antioxidant supplement, but MSK also notes that oral NAC was poorly absorbed in mechanistic kidney studies.
What the research shows
| Use | What MSK reports |
|---|---|
| Drug-induced liver injury | Clinical studies show NAC can treat it (as medical care) |
| Chronic lung disease (COPD) | Mixed; not the most effective mucolytic |
| Depression, compulsive disorders | Mixed results |
| Kidney protection from contrast dye | Benefit lost in larger studies; oral NAC poorly absorbed |
| Cancer prevention | Did not prevent second head, neck or lung tumors in a large trial |
Lungs. Some studies suggest NAC can reduce flare-ups and inflammation and help maintain lung function, but other trials found no benefit, and a meta-analysis suggests it is not the most effective mucus-thinning agent for COPD.
Mood and behavior. There has been interest in NAC for psychiatric conditions, but studies are mixed for compulsive disorders and depression.
Cancer care. Preliminary findings suggest NAC may reduce some treatment side effects, such as liver toxicity, neuropathy and mouth sores, but it did not reduce cisplatin toxicities, and it is unclear whether it changes how well cancer treatment works. In an animal model, NAC appeared to speed lung cancer growth, so more study is needed.
Side effects and interactions
- Common. Stomach upset, diarrhea, nausea, vomiting, fatigue, eye irritation and skin rash.
- Less common. Low blood pressure, anaphylaxis, asthma attacks and headache have been reported.
- Nitroglycerin. Adding NAC caused severe headaches in people because of extra blood vessel widening.
- Antidepressants. In animal studies, NAC may increase the effects of imipramine and escitalopram; human relevance is unknown.
- Cancer treatment. Ask your oncology team before using NAC during chemotherapy or radiation.
- Pregnancy and medicines. NOW Foods advises consulting a physician if you are pregnant, nursing, taking medication or have a medical condition.
NAC's legal status
NAC has an unusual history. The FDA has determined that NAC is excluded from the legal definition of a dietary supplement because it was approved as a new drug before it was sold as a supplement or food. However, NAC supplements have been sold in the U.S. for over 30 years.
In August 2022, the FDA finalized guidance saying it intends to use enforcement discretion for certain NAC products labeled as dietary supplements, meaning it does not plan to act against them while it reviews the issue. The FDA said its initial review had not revealed safety concerns, and in November 2023 it added its NAC safety review to its peer review agenda.
How to choose an NAC supplement
- NAC amount. NOW Foods' NAC gives 600 mg per capsule, taken twice daily, with 25 mcg of selenium.
- Check for selenium. If you already take a multivitamin with selenium, add up your total.
- Freshness. NOW Foods advises keeping the bottle tightly closed and the freshness packets inside, and notes natural color changes can occur when the product is exposed to air.
- Blends. Some products combine NAC with glutathione or liver herbs. Check each ingredient amount.
- Medical uses stay medical. Acetaminophen overdose is an emergency. Get emergency care, and never self-treat with a supplement.
What to look for when you buy
NAC 600 mg capsules with selenium
Best for: Adults who want the common 600 mg NAC form
NOW Foods lists 600 mg NAC with 25 mcg selenium per capsule, taken twice daily.
Watch out: Can cause stomach upset and nausea. Severe headaches reported with nitroglycerin. Count selenium from other supplements.
See options on AmazonNAC without added ingredients
Best for: People who want NAC alone
Single-ingredient NAC capsules are widely sold, making it easier to track what you take.
Watch out: Same side effects and interaction cautions. Store tightly closed.
See options on AmazonNAC with glutathione
Best for: Buyers comparing antioxidant combinations
NAC is a glutathione precursor, and some products pair the two.
Watch out: Combinations add ingredients and were not what most NAC studies tested.
See options on AmazonQuestions people ask
- What is NAC supplement good for?
- It is sold for liver and immune support. As a drug, NAC treats acetaminophen overdose. Evidence for lungs and mood is mixed.
- Is NAC legal to sell as a supplement?
- The FDA says NAC is technically excluded from the supplement definition but announced enforcement discretion in 2022 for certain NAC supplements while it reviews the issue.
- What are NAC side effects?
- Stomach upset, diarrhea, nausea, vomiting, fatigue, eye irritation and rash are most common.
- How should I take NAC?
- Follow the label. NOW Foods directs 1 capsule twice daily.
- Can I take NAC with nitroglycerin?
- Ask your doctor. The combination caused severe headaches in people.
Sources
- N-Acetylcysteine (mskcc.org), Memorial Sloan Kettering Cancer Center, About Herbs
- FDA Releases Final Guidance on Enforcement Discretion for Certain NAC Products (fda.gov), U.S. Food and Drug Administration
- NAC 600 mg Veg Capsules (www.nowfoods.com/products/supplements/nac-600-mg-capsules), NOW Foods