NAC Supplement Guide (2026): What It Does, Dose & What to Buy

What NAC is

NAC (N-acetylcysteine) is a form of cysteine, an amino acid. Your body can use the cysteine in NAC to make glutathione, an antioxidant your cells make. Researchers say this matters most when glutathione runs low, and that NAC is likely to do little in cells that already have enough (Rushworth 2014). Hospitals also use NAC as a drug: it is given by IV or by mouth for an acetaminophen (Tylenol) overdose (Bebarta 2010). That is a drug use, not a supplement use.

What the trials tested

This table shows what studies tested. It is not advice to treat any condition. Talk to your doctor before you use NAC for a health problem.

Each row says what a study tested and what happened compared with a dummy pill (placebo). The amounts each trial used are in the NAC dosage guide.

How much NAC to take

The bottles we compared say to take 600 to 1,800 mg a day: from 1 capsule a day (Nutricost) up to 3 a day (Life Extension, Pure Encapsulations). Trials used 600 to 3,000 mg a day, and many used 1,200 mg, taken as 600 mg twice a day. Studies disagree on whether 600 mg is enough.

Nutricost’s label says 1 capsule a day (600 mg), about $0.10. Many trials used 2 capsules’ worth (1,200 mg), about $0.20 a day. Ask your doctor before you take more than the label says.

NAC dosage guide → the amount each trial used, both sides of “is 600 mg enough?”, and how many capsules of each product make your amount.

Why most NAC on the shelf doesn’t count

Most products that contain NAC are blends with only a little of it. Of the 482 NAC labels we checked that list an amount, about 4 in 5 are blends such as liver or detox formulas, and a typical blend gives 100 mg a serving; plain NAC capsules usually give 600 mg. The full breakdown.

A blend can still be a fine product for its other ingredients. It just won’t give you as much NAC as one plain capsule.

Which NAC to buy

Our pick, Nutricost NAC 600 mg, is at the top of the page: $0.10 for 1 capsule (600 mg), $0.20 for 2. If you want something else:

1. If you want 1,200 mg or more in one serving

   Toniiq NAC 1300
   8.5/10 · $0.12 per 600 mg · $0.25 for its 2-capsule serving (1,300 mg)

   Check price for Toniiq NAC 1300

   1,300 mg in 2 capsules (650 mg each), the only one of the 8 with 1,200 mg or more in one serving. Its label says 2 capsules a day on an empty stomach.

2. If you want an outside lab check

   Thorne NAC 500 mg
   6.5/10 · $0.44 per 600 mg · $0.37 for its 1-capsule serving (500 mg) · NSF/ANSI 173

   Check price for Thorne NAC 500 mg

   The only one of the 8 on a public testing list (NSF/ANSI 173), which checks that the bottle holds what the label says. It costs more than 4 times as much as our pick per 600 mg. Its label says 1 capsule two or three times a day (1,000 to 1,500 mg).

3. If you want a slow-release tablet

   Jarrow N-A-C Sustain 600 mg
   5.0/10 · $0.37 per 600 mg (1 tablet)

   Check price for Jarrow N-A-C Sustain 600 mg

   A 600 mg tablet made to release part of its NAC quickly and part slowly. It is the only slow-release option of the 8, and it costs more than most.

4. If you want the lowest cost

   BulkSupplements NAC powder
   7.0/10 · $0.055 per 600 mg (1 scoop)

   Check price for BulkSupplements NAC powder

   Powder you measure yourself: 600 mg is about ¼ teaspoon. It costs about half as much as our pick. Like all NAC it smells of sulfur, and you taste it more as a powder.

Costs are each brand’s own list price for the bottle we link, checked October 15, 2026. Prices on Amazon differ.

Every NAC we compared

A dash means we found the product on none of the five public testing lists we searched. Nutricost and Toniiq say they are third-party tested but publish no lab results. Pure Encapsulations sells nothing on its own site, so we have no list price and give it no score. Best NAC supplements, ranked.

Side effects and who should skip NAC

• At supplement doses, close to a dummy pill. At supplement doses, side effects were close to placebo: in the 1-year trial at 1,200 mg a day, 29% of people on NAC reported a side effect, vs 26% on a dummy pill (Zheng 2014). The 2015 review found side effects no more common at higher doses (Cazzola 2015).
• Upset stomach. It is the most common complaint. In a 2025 trial at 2,400 mg a day, 63 of 98 young people on NAC reported stomach side effects, vs 37 of 94 on a dummy pill (Gray 2025). Taking it with food, and splitting larger amounts into two doses, may help.
• A sulfur smell. NAC contains sulfur, so capsules can smell like rotten eggs. That is normal, not a sign the bottle has gone bad.
• By mouth vs IV. At the very large doses hospitals give for acetaminophen overdose, about 1 in 4 people (23%) felt sick or threw up when NAC was given by mouth, vs 9% when it was given by IV (Bebarta 2010). The serious allergy-like reactions you may read about come mostly from IV NAC in hospitals: 6% of IV patients vs 2% by mouth, in the same hospital study (Bebarta 2010).

Ask your doctor before you take NAC if any of these apply:

• Nitrates (such as nitroglycerin for chest pain): in a hospital study, adding NAC to IV nitroglycerin caused low blood pressure with symptoms in 7 of 24 people, vs 0 of 22 on nitroglycerin alone (Horowitz 1988). Ask your doctor before you take NAC with any nitrate.
• Blood thinners, or surgery coming up: tell your doctor you take NAC. Taken with nitroglycerin, NAC can form a compound that strongly slows blood clotting (Horowitz 1988). We found no study of NAC capsules alone and bleeding.
• Asthma: doctors who reported a fatal reaction to IV NAC in a person with severe asthma warn that asthma raises the risk of reactions to NAC (Appelboam 2002). Capsules are a different route, but tell your doctor you take NAC. Inhaled NAC, a breathing medicine used in hospitals, can now and then tighten the airways, even in people who used it before without trouble. Its drug label says people with asthma should be watched closely. (drug label)
• Jarrow’s label warns that taking a lot of NAC for a long time can change liver test results without harming the liver. Tell your doctor you take NAC before a blood test.
• Pregnancy and breastfeeding: there is not enough research on NAC supplements. Ask your doctor first.

NAC vs glutathione

Glutathione is an antioxidant your cells make from three amino acids, one of them cysteine. NAC supplies cysteine, and researchers say it refills glutathione mainly when it runs low (Rushworth 2014). You can also buy glutathione itself as a supplement. Every trial in the table above used NAC, not glutathione. Glutathione supplements compared.

Why NAC disappeared from Amazon, and came back

1. July 2020FDA sent warning letters to supplement makers. It said NAC cannot be sold as a supplement, because it was approved as a drug first, in 1963. (FDA)
2. Spring 2021Amazon began taking NAC supplements off its store. (SupplySide)
3. End of 2021About 718 NAC listings on Amazon in late 2020 had fallen to zero, a supplement trade group official said. (Nutraceuticals World)
4. August 2022FDA said it will not currently act against NAC supplements that follow the other rules and make no disease claims. (FDA)
5. August 25, 2022Amazon confirmed it was selling NAC again. (Natural Products Insider)
6. October 2026NAC is on sale on Amazon. On October 15, 2026, we checked 24 NAC listings, and all 24 could be bought.

FDA says NAC is not technically allowed in dietary supplements, because it was approved as a drug first. Since August 2022, FDA says it will not currently act against NAC supplements that follow the other rules and make no disease claims. FDA has said it is considering a rule to allow NAC in supplements. As of October 15, 2026, no proposed rule has been published, and FDA says it could change this policy.

Frequently asked questions

NAC guides

Sources

1. Cazzola M, et al. Influence of N-acetylcysteine on chronic bronchitis or COPD exacerbations: a meta-analysis. Eur Respir Rev. 2015. PubMed 26324807
2. Zheng JP, et al. Twice daily N-acetylcysteine 600 mg for exacerbations of COPD (PANTHEON). Lancet Respir Med. 2014. PubMed 24621680
3. Grant JE, et al. Trichotillomania trial. Arch Gen Psychiatry. 2009. PubMed 19581567
4. Grant JE, et al. Skin-picking (excoriation) trial. JAMA Psychiatry. 2016. PubMed 27007062
5. Eghdami S, et al. Review of NAC added to SSRIs in OCD. Front Psychiatry. 2024. PubMed 39376972
6. Viña I, et al. Efficacy of N-acetylcysteine in polycystic ovary syndrome. Nutrients. 2025. PubMed 39861414. Shahveghar Asl Z, et al. Br J Nutr. 2023. PubMed 36597797
7. Gray KM, et al. N-acetylcysteine for cannabis use disorder in adults. Drug Alcohol Depend. 2017. PubMed 28623823. Gray KM, et al. Youth trial. Neuropsychopharmacology. 2025. PubMed 39910268
8. Rushworth GF, Megson IL. Existing and potential therapeutic uses for N-acetylcysteine: the need for conversion to intracellular glutathione for antioxidant benefits. Pharmacol Ther. 2014. PubMed 24080471
9. Bebarta VS, et al. Safety of oral versus IV acetylcysteine for acetaminophen overdose. Clin Toxicol. 2010. PubMed 20524832
10. Horowitz JD, et al. Combined use of nitroglycerin and N-acetylcysteine in the management of unstable angina pectoris. Circulation. 1988. PubMed 3127076
11. Appelboam AV, et al. Fatal anaphylactoid reaction to N-acetylcysteine: caution in patients with asthma. Emerg Med J. 2002. PubMed 12421803
12. Acetylcysteine inhalation solution, prescribing information (warnings and adverse reactions). DailyMed. Jarrow N-A-C Sustain label warning: NIH label 323064.
13. FDA. Policy Regarding N-acetyl-L-cysteine (August 2022; read October 15, 2026). Amazon history: SupplySide, Nutraceuticals World and Natural Products Insider, linked in the timeline.
14. NIH Dietary Supplement Label Database: label 304777, and 900 NAC labels; our analysis. Label directions: each product’s Supplement Facts panel.

This page is for information. It is not medical advice.