What Is N-Acetylcysteine?

N-Acetylcysteine powder, tablets, and capsules

Verywell / Anastasia Tretiak

N-acetylcysteine (NAC) is the synthetic form of the amino acid cysteine. Cysteine is considered a nonessential (or semi-essential) amino acid. This means you get cysteine in your diet from the foods you eat, but your body can also produce cysteine from other amino acids.

If you've taken NAC as a supplement, you may have heard claims that it can protect against certain health concerns, like respiratory diseases, heart disease, and psychiatric disorders.

The Food and Drug Administration (FDA) approved NAC for the treatment of acetaminophen (Tylenol) poisoning. This would be provided under medical supervision in a hospital setting. NAC is also approved as an add-on mucolytic therapy. It helps break apart mucus in certain lung conditions.

In July 2020, the FDA reminded manufacturers that an approved drug, such as NAC, could not be sold as a dietary supplement. However, the FDA is considering implementing a rule permitting the use of NAC in products labeled as dietary supplements.

While fewer manufacturers are selling NAC, it continues to be available as a dietary supplement.

This article explains the uses of NAC as a supplement, side effects, and precautions.

Supplement Facts

  • Active Ingredient: Cysteine
  • Alternate Name(s): Acetylcysteine, L-cysteine
  • Legal Status: FDA-approved drug
  • Recommended Dose: Taken orally 600-1,200 mg/day is most common
  • Safety Considerations: Taken orally, likely safe. May interact with other medications. Given intravenously, should be medically supervised. Mild side effects reported.

Uses of N-Acetylcysteine

The use of NAC should be individualized and vetted by a healthcare provider. No supplement is intended to treat, cure, or prevent disease.

It is important to note that there is little to no evidence to back up health claims. Most of the purported benefits below are not backed by sufficient evidence. Even those claims for which there is at least some research typically fall short. That said, there have been some positive findings that warrant further research.

Some research shows that supplementing NAC will increase the amount of glutathione in the body. Glutathione is a powerful antioxidant. To create glutathione, NAC bonds with two other amino acids—glutamine and glycine. Glutathione plays essential roles in the body, including:

Integrative medicine practitioners suggest that since NAC can increase glutathione production, it might prevent and manage some health conditions. These include:

Some suggest that NAC would help prevent or manage certain types of cancer, cirrhosis or hepatitis, kidney disease, lupus, and more. However, there is no evidence to support these claims.

You should not use NAC supplements for the sole treatment or prevention of any of the above conditions.

Acetaminophen (Tylenol) Poisoning

Healthcare providers administer NAC to treat Tylenol (acetaminophen) poisoning by giving three consecutive intravenous (IV) infusions of NAC over 21 hours. This treatment helps prevent liver damage and other symptoms of acetaminophen toxicity.

When to Seek Medical Treatment

Never try to treat a Tylenol overdose yourself. Tylenol poisoning is considered a medical emergency. Call 911 immediately if you or someone you know may have overdosed on acetaminophen.

COPD

Some studies have looked into the benefits of NAC in people with chronic bronchitis and COPD.

A 2015 meta-analysis published in European Respiratory Review evaluated 13 studies and 4,155 people with COPD. It concluded that 1,200 milligrams of NAC per day reduced the incidence and severity of flares compared to a placebo.

COVID-19

Due to the antioxidant and anti-inflammatory characteristics of NAC, it has been used in clinical practice for people hospitalized with COVID-19.

A 2021 study published in Infectious Diseases looked at the effects of NAC supplementation. Supplementing 600 mg NAC orally twice daily for 14 days resulted in reduced disease progression, reduced need for intubation, and reduced mortality. However, the study authors concluded that these findings need to be confirmed by properly designed prospective trials.

Further research is needed and two clinical trials are already underway.

Heart Disease

Proponents of NAC say that it may help lower the risk of heart disease by reducing the oxidative stress on the heart. Oxidative stress occurs when an imbalance of free radicals damages your body's cells and tissues.

This benefit may be shown in research where daily use of NAC reduced hypertension (high blood pressure). Hypertension is a significant factor for atherosclerosis (plaque build-up in the arteries).

According to a 2015 study in the American Journal of Clinical Nutrition, a significant drop in systolic and diastolic blood pressure was noted in those supplementing NAC over four weeks. These drops occurred regardless of whether a person smoked, their weight, or their blood lipid values.

The same study also found that NAC reduces your blood's homocysteine levels. High levels of homocysteine can increase your risk of heart disease. However, the long-term effects of NAC on blood pressure are unknown.

This study was limited by its low participant number.

Male Infertility

Research has looked at whether NAC may further improve fertility in people with varicoceles. Varicoceles is a condition with enlarged veins in the scrotum and testicles. It is one of the leading causes of male infertility.

According to a 2016 study in the International Journal of Fertility and Sterility, people who underwent surgery to treat varicoceles had higher conception rates if they took NAC before and after surgery. However, this study was preliminary and only had 35 participants.

Polycystic Ovary Syndrome

NAC may help alleviate symptoms of PCOS, according to a 2015 systematic review in Obstetrics and Gynecology International.

The review evaluated eight studies with a total of 910 women with PCOS. The investigators found that NAC improved ovulation and pregnancy rates compared to a placebo. However, the improvement was not as great as it was with metformin. Metformin is a prescription drug used to treat PCOS.

The researcher also reported that NAC did not improve other common symptoms of PCOS, such as menstrual irregularities or weight gain.

Psychiatric Disorders

NAC may play a role in glutamate dysregulation and inflammation, which are apparent in psychiatric conditions. NAC supplementation has been studied as a possible adjunctive (add-on) therapy for several psychiatric disorders:

  • Mood disorders: NAC supplementation may improve depression or bipolar disorder symptoms, but results are mixed, and further research is needed.
  • Obsessive-compulsive disorder (OCD): NAC supplementation has been studied for its use in reducing the severity of symptoms. However, the results are mixed.
  • Schizophrenia: A 2019 study in Psychological Medicine found that NAC supplementation improved symptoms in schizophrenia.
  • Substance abuse disorders: The research results are mixed, but NAC supplementation may have a role in substance abuse treatment, especially involving cocaine and cannabis.

NAC supplementation should not be used as an alternative to the medical treatment of psychiatric disorders. It should only be considered for use in addition to the treatment prescribed by a healthcare professional.

Recap

While some practitioners tout a myriad of health benefits from NAC supplementation, very few are supported by research. Of those that are, studies are small, and the evidence is limited. Therefore, more research is needed.

Cysteine Deficiency

Since cysteine is made in the body and found in high protein foods, deficiency is rare. Vegetarians may be at risk of deficiency, especially if their intake of cysteine-rich plant foods is low.

Side Effects

You may decide to try supplementing NAC orally or it can be prescribed by a healthcare provider. In both instances, it is important to know there are possible side effects.

NAC is generally considered safe and well-tolerated when used appropriately.

Common Side Effects

When taken orally, common side effects are mild and typically resolve on their own. These may include:

  • Nausea
  • Vomiting
  • Stomach ache
  • Diarrhea

If inhaled, you may experience a runny nose, drowsiness, tightness in the chest, and numbness of the mouth. Healthcare providers will need to monitor you for reactions if you have asthma.

Severe Side Effects

Allergies to NAC are uncommon but can occur. The risk is highest during NAC infusions. In rare cases, an infusion may cause anaphylaxis, a life-threatening allergic reaction.

Side effects of taking NAC orally are typically mild and may include nausea, vomiting, and diarrhea. Intravenous NAC should be medically supervised in case anaphylaxis occurs. If you think you are experiencing a side effect from NAC supplementation, call your healthcare provider.

Precautions

The FDA recently made it known that it considers NAC an FDA-approved drug. Therefore, it can not be sold as a dietary supplement. However, NAC has been in supplements for years.

Some nutrition organizations have petitioned the FDA to change this. The FDA denied the petitions to define NAC as a dietary supplement. However, they are considering implementing a rule permitting the use of NAC in products labeled as dietary supplements.

Although NAC is generally safe when used appropriately, there are a few instances when it may not be safe to use it:

  • Pregnancy or breastfeeding: If you are pregnant or breastfeeding, speak with your healthcare provider or OB/GYN before taking NAC. They will help you assess the risks and benefits of NAC as they pertain to your situation and whether you need the supplement or not.
  • Children: A safe and effective oral dose of NAC in children has not been established. Therefore, unless directed by a healthcare provider, children should not take NAC supplements.
  • People with bleeding disorders: NAC can slow blood clotting. Therefore, people with bleeding disorders, such as hemophilia or Von Willebrand disease, should avoid taking NAC.
  • People with kidney disease: Research is conflicting on the benefits of NAC for those with kidney disease. Therefore, there are no established guidelines for dosage or use. If you have kidney disease, check with your healthcare provider first before using NAC.
  • People with asthma: People with asthma should use caution with NAC unless done under medical supervision. NAC may cause bronchospasm when inhaled or taken orally.

Avoid supplementing NAC in combination with some medications unless medically supervised. Refer to interactions for further details.

Since NAC may affect blood tests and slow blood clotting, it is suggested to avoid 12 hours before a blood draw and for 2 weeks before elective surgeries.

Dosage of NAC

Oral NAC supplements are available over the counter (OTC) in several formulations, including tablets, capsules, and powders.

Most are sold in 500-milligram (mg) dosages, although some are as high as 1,200 mg. Product suggested doses range from 1 to 4 doses per day for a total of 500 mg to 3,000 mg daily.

However, since the FDA does not regulate supplements, there are no universal guidelines on the appropriate use of NAC. Therefore, you should use caution and work with a qualified healthcare provider when considering this (and any) supplement.

Always speak with a healthcare provider before taking a supplement to ensure that the supplement and dosage are appropriate for your individual needs.

What Happens If I Take Too Much?

There are no reports of toxicity with oral NAC supplementation. However, taking too much NAC may make you more likely to experience side effects.

Death has occurred as a result of an accidental overdose of intravenous NAC.

Interactions

NAC has few known drug interactions. However, it may intensify or interfere with the action of some medications, including:

  • Angina medications: NAC may intensify the effects of nitrates used to treat angina. These increased effects may cause severe headaches.
  • Blood thinners: NAC may further contribute to bleeding. If you are on blood thinners, it is recommended to avoid using NAC, unless medically supervised.
  • Antihypertensive medication: NAC may further contribute to lowering blood pressure leading to hypotension. This is also true with other herbal products and supplements including casein peptides, L-arginine, niacin, and stinging nettle.
  • Activated charcoal: NAC supplementation may interfere with its intended action.
  • Chloroquine: NAC supplementation may interfere with its intended action.

How to Store NAC

NAC supplements should be stored at room temperature in a cool, dry room. Discard any supplements that have expired, are discolored, or show signs of deterioration.

It is important to note that NAC may have an odor similar to sulfur, which is normal.

How to Buy

The amino acid, cysteine, occurs naturally in foods, like chicken, turkey, red peppers, and garlic. However, NAC does not occur naturally in foods. It is the synthetic form of cysteine used in medications or supplements.

In the United States, NAC is considered a drug. Many manufacturers and sellers have pulled the products as a result of the FDA statement.

Yet, NAC is still available over-the-counter in several formulations, including:

  • Tablets
  • Capsules
  • Softgels
  • Effervescents
  • Powders

Dietary supplements are not regulated in the United States. This means the FDA does not approve them for safety and effectiveness before products are marketed.

When possible, choose a supplement that has been tested by a trusted third party, such as U.S. Pharmacopeia (USP), ConsumerLabs, or NSF. However, even if supplements are third-party tested, that doesn't mean that they are necessarily safe for all or effective in general.

It is important to talk to your healthcare provider about any supplements you plan to take. Check with them about any potential interactions with other supplements or medications.

N-acetylcysteine tablets
Verywell / Anastasia Tretiak

Summary

NAC is an FDA-approved drug for the treatment of acetaminophen poisoning. Recently, the FDA has stated that NAC should not be sold as a dietary supplement since it is already an approved drug. However, the FDA is considering a ruling that would permit NAC to be used in dietary supplements.

Oral NAC supplements have been suggested to help manage symptoms related to COPD, heart disease, PCOS, psychiatric conditions, and more recently COVID-19. Evidence to support these benefits is limited and more research is needed. Talk to your healthcare provider about whether NAC is appropriate for you.

Frequently Asked Questions

  • Does NAC help with COVID-19?

    There has been some evidence that N-acetylcysteine along with other antiviral treatments could help people with COVID-19 avoid serious symptoms and complications such as hospitalization, ventilation, or death.

    However, more research is needed to confirm its effectiveness. A number of clinical trials have been developed to further investigate NAC’s use for treating COVID-19.

  • Can taking N-acetylcysteine help you get pregnant?

    It depends on the issues that are preventing you from getting pregnant. NAC has been shown to improve male fertility and may help people with PCOS conceive.

  • Is it safe to take N-acetylcysteine every day?

    In most cases, it should be safe for adults to take 600 mg once or twice a day. However, talk to your healthcare provider to be sure these supplements will not interfere with other medications you take or existing medical conditions.

Originally written by
Cathy Wong
Cathy Wong

Cathy Wong is a nutritionist and wellness expert. Her work is regularly featured in media such as First For Women, Woman's World, and Natural Health.

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