Product Reviews
NAC (N-Acetyl Cysteine) Supplements Review

Reviewed and edited by Tod Cooperman, M.D. Tod Cooperman, M.D.
Posted: 2/15/2019 Last update: 7/16/2019
N-acetyl cysteine (NAC) supplements tested by
Sections: Jump to a section by clicking on its name.
  • What is it? NAC is a synthetic compound that is converted to glutathione in the body (see What It Is).
  • Does it work? NAC has a wide variety of uses — although not all are well-proven. As a prescription drug it is used to treat acetaminophen poisoning (to protect the liver), but general claims of "liver protection" are not well established. It has also been used in inhaled form to loosen mucus in people with cystic fibrosis, and orally it may help with symptoms of flu, chronic bronchitis and COPD symptoms, but evidence is weak for its purported ability to thin mucus during a cold and general claims of "immune support." (See What It Does).
  • What did CL find? ConsumerLab found the cost to obtain 600 mg of NAC ranged over 15-fold from just 4 cents to as much as 63 cents. A single dose of NAC ranged from 500 to 1,000 mg. Quality-wise, all products contained their claimed amounts of NAC, although one also contained a significant amount of sodium. (See What CL Found and use the Results table to compare the amounts of NAC and sodium in products).
  • Top Picks — ConsumerLab selected Top Picks for NAC as a powder, capsule, and tablet based on quality, value, and other features.
  • What to look for? NAC is always in the "free form" so if you see this on a label, it's nothing you should pay more for. Just choose a product that provides the dose you want at a low cost -- generally 4 to 15 cents per 600 mg. (See ConsumerTips).
  • How much to take and when? The dose of NAC used in clinical trials has ranged from about 600 mg to 3,000 mg per day, typically divided into two or three servings. See the What It Does section for the dosage for specific uses.
  • Cautions: NAC can cause headache and gastrointestinal side effects. It can also worsen asthma. For details, see Concerns and Cautions.

What It Is:
NAC (N-acetyl cysteine), which is also known as just acetylcysteine, is a synthetically modified form of the amino acid cysteine (cysteine occurs naturally in foods, whereas NAC does not). In the body, NAC is converted to the antioxidant glutathione.

NAC is not an essential nutrient and there is no recommended daily allowance.

What It Does:
N-acetyl cysteine is available as a dietary supplement (taken orally) as well as a prescription medication. As a prescription medication, NAC in solution is given orally or intravenously to treat acetaminophen (Tylenol®) poisoning, as it helps replenish glutathione in the liver which is depleted by high doses of acetaminophen). Preliminary studies in animals suggest that when taken with large doses of acetaminophen, NAC may help protect the liver from acetaminophen-induced liver damage, and may even increase the anti-inflammatory effects of acetaminophen (Owumi Drug Dev Res 2015; Qiu Vet Immunol Immunopathol 2013), but no human studies have evaluated this. A small study in people with advanced cancer suggests that intravenous NAC taken within 8 hours after very high doses acetaminophen seemed to protect the liver (Kobrinsky, Cancer Invest 1996). NOTE: NAC is often promoted as supporting the liver, likely based on its effect in acetaminophen poisoning. However, a general liver-protectant effect has not been established.

NAC has been used in combination with nitroglycerine, to treat angina, but results have been mixed.

An inhaled aerosolized NAC solution ("a mist") is also used to help loosen and clear mucus in the airways of patients with cystic fibrosis. (Note: These conditions should be treated only under medical supervision; do not attempt to treat with oral NAC supplements).

One placebo-controlled clinical study found 600 mg of NAC taken twice daily during flu season (October — April) did not prevent infection but significantly reduced flu symptoms in people who contracted the flu virus (De Flora, Eur Respir J 1997). Among individuals taking NAC who became infected, only 25% became symptomatic, versus 79% in the placebo group. There is some preliminary evidence that NAC supplementation may improve certain blood markers of immune system function. For example, a small study among postmenopausal women in Brazil found that 600 mg of NAC (taken as an effervescent tablet dissolved in half a glass of water) daily at bedtime for four months increased natural killer cell activity and improved other measures of immune system function compared to before supplementation. However, the study was not placebo-controlled and did not report the occurrence of illness (colds, flus, etc.) (Arranz, Free Radic Biol Med 2008). NAC supplementation has also been reported to restore natural killer cell activity in individuals with HIV (Droge, Proc Nutr Soc 2000). There is not sufficient evidence to suggest that NAC supplementation "boosts" the immune system to the extent that it will reduce the occurrence of illness.

NAC may decrease the frequency of flare-ups of chronic bronchitis and COPD (chronic obstructive pulmonary disease). An analysis of eight clinical trials found that 400 mg to 600 mg of NAC taken daily for 3 to 6 months significantly reduced exacerbations of chronic bronchitis (Grandjean, Clin Ther 2000). In another clinical study, COPD patients who received 600 mg of NAC in addition to standard treatment medications daily for six months had significantly fewer flare-ups than those who received only medication (Pela, Respiration 1999).

Because of its mucus-thinning properties, NAC is sometimes promoted for clearing nasal congestion due to colds or sinusitis. NAC has been shown in laboratory studies to thin nasal mucus when applied directly to mucus samples (Rhee, Arch Otolaryngol Head Neck Surg 1999) and to increase nasal flow when inhaled in combination with a decongestant (Cogo, Arzneimittelforschung 1996). However, there is little clinical evidence that oral supplementation reduces the amount or thickness of nasal mucus: A preliminary study in Iran suggested a beneficial effect but, strangely, lacked details about dosage, and a study to have been conducted in Canada was either not completed or not published.

In women being treated for infertility associated with polycystic ovarian syndrome, taking 1,200 mg NAC daily along with the fertility drug clomiphene citrate was shown to significantly increase rates of ovulation and pregnancy compared to treatment with clomiphene citrate alone (Rizk, Fertil Steril 2005).

A small double-blind clinical trial in people with Sjogren's syndrome found that 200 mg of NAC taken 3 times per day improved eye-related symptoms such as eye soreness and irritation, (Walters, Scand J Rheumatol Suppl 1986).

In patients with end-stage renal failure, 600 mg of NAC twice daily reduced the incidence of cardiovascular events, including stroke and heart attack, by 40% compared to placebo, although it did not reduce overall mortality (Tepel, Circulation 2003). NAC (also called acetylcysteine) has been used to prevent kidney injury in patients undergoing angiography (imaging of blood vessels); however, a large study found that giving 1,200 mg of NAC one hour before and after angiography and twice daily on the following four days provided no benefit compared to placebo (Weisbord, NEJM 2017)

NAC has been found to lower homocysteine levels. High levels of homocysteine are associated with a higher risk of heart disease, although it is not necessarily a causative factor. In a small clinical study, effervescent tablets containing 2,000 mg of NAC dissolved in water and taken twice daily for two weeks lowered homocysteine levels by 45% compared to placebo (Wiklund, Atherosclerosis 1996).

There is some evidence that NAC may help reduce the severity of symptoms in certain mental health disorders. One randomized, double-blind clinical trial in people with schizophrenia found 1, 000 mg of NAC taken twice daily in addition to maintenance medications significantly improved scores on symptom scales and decreased restlessness compared to the medications plus placebo (Berk, Biol Psychiatry 2008). A more recent study of patients with chronic schizophrenia taking risperidone found that NAC supplementation (up to 2,000 mg per day) resulted in significantly improved scores on tests of negative symptoms compared to risperidone plus a placebo (Farokhnia, Clin Neuropharmacol 2013).

Several small but well-controlled clinical studies (all by the same lead researcher) indicate NAC may also be helpful in reducing compulsive behavior -- possibly by affecting glutamate concentrations in the nucleus accumbens of the brain. In a study involving adults with excoriation (skin picking) disorder, 1,200 to 3,000 mg of NAC per day or placebo was taken for 12 weeks (the dose increased to 2,400 mg at week 3 and to 3,000 mg at week 6) along with existing medications. Compared to placebo, NAC treatment was associated with significant improvements: 47% of the NAC group was "much or very much" improved versus 19% of the placebo group, and scores on an obsessive-compulsive excoriation scale decreased from 18.9 to 11.5 in the NAC group, versus 17.9 to 14.1 in the placebo group. However, quality of life scores did not change significantly for either group. The researchers concluded that benefits appear to be "primarily in the reduction of urges or cravings to pick rather than the actual behavior" "suggesting that NAC might be more effective in people who pick automatically or with little conscious awareness." (Grant, JAMA Psych, 2016). In men and women with trichotillomania (anxiety-related compulsive hair-pulling) 1,200 mg to 2,400 mg of NAC taken daily for 12 weeks significantly reduced hair-pulling symptoms compared to placebo (Grant, Arch Gen Psychiatry 2009). Another study found daily supplementation with NAC (about 1,500 mg per day) improved measures of obsessive-compulsive behavior in people with pathological gambling (Grant, Biol Psychiatry 2007).

High doses of NAC were reported to reduce symptoms in four patients with progressive myoclonus epilepsy. In the study, the patients were given vitamin E, selenium, riboflavin, zinc and magnesium for six months, which resulted in improvements in awareness and speech. They were then also given 4, 000 to 6,000 mg of NAC daily, plus magnesium, for over two years. During treatment with NAC, myoclonus (involuntary jerking) was decreased (Hurd, Neurology 1996).

People with Parkinson's disease given 500 mg of NAC orally daily in addition to 50 mg/kg (about 3,500 mg) of NAC intravenously weekly for a period of three months showed significantly improved symptoms as well as slightly increased dopamine transporter binding in brain areas compared to people in a control group given standard care in a small study in Philadelphia. There were no significant adverse events. Caveats to this study are that it was not placebo-controlled and any contribution of the oral NAC is likely much smaller than that NAC given intravenously. As to a mechanism of action, the researchers noted that oxidative damage occurs in the brains of Parkinson's patients and NAC may help by increasing levels of the antioxidant glutathione (Monti, Clin Pharm Ther 2019).

See the Encyclopedia article for more details about the clinical uses of NAC.

Quality Concerns and What CL Tested For:
Neither the Food and Drug Administration (FDA) nor any other federal or state agency routinely tests supplements for quality prior to sale. In order to help consumers identify products of better quality. tested NAC supplements to determine whether the amounts of NAC listed on labels matched those in the products. All products in regular tablet/caplet form also underwent disintegration testing to check if they would break apart properly in solution.

See How Products Were Evaluated for more information on testing.

What CL Found:
All eight of the NAC supplements that selected for review passed testing, as did three supplements tested through's Quality Certification Program.

The tested products provided 500 mg or 600 mg of NAC per capsule, 900 mg or 1,000 mg per tablet, or, among the powders, 600 mg per very small scoop or 1,200 mg per small scoop.

The total suggested daily serving sizes ranged from one to four pills per day, yielding 500 mg to 3,000 mg of NAC. These amounts are generally in line with what has been used in clinical studies.

"Free form":
In the Supplements Facts panels on the products, some, like Solgar, list the amount of NAC in "free form" while others do not. With supplement ingredients that need to be stabilized in salt forms, this distinction can be important because the free form typically indicates just the weight of the active molecule and not the attached stabilizer. However, NAC is always in "free form," so this is not an important factor. That is, even those products which did not indicate whether the NAC was "free form" were in the free form.

Since all of the products contained their listed amounts of NAC and there were no problems with tablet disintegration, you may want to choose a product based on price and, possibly, other special features. We calculated the cost to get an equivalent amount of NAC (600 mg) from each product, as shown in the graph below (as well as in brackets the last column of the Results table). The cost to obtain 600 mg of NAC ranged over 15-fold from as just 4 cents from a powder (and 6 cents from a pill) to as much as 63 cents from an effervescent tablet.

Cost per 600 mg of NAC

Top Picks
Our Top Picks, based on being high-quality and lowest cost for NAC, are the following:

Powder: Nutricost NAC, which provides 1,200 mg of NAC per small scoop (for 9 cents), was the lowest cost source of NAC — just 4 cents per 600 mg. If you want less than 1,200 mg (a relatively high single dose), it's easy to use less powder. The powder is meant to be mixed into water or other beverage, but be aware that NAC naturally has a very tart flavor.

Capsule: The capsule that provided NAC at lowest cost (10 cents per 600 mg of NAC in a vegetarian capsule) was Doctor's Best NAC Detox Regulators. It includes 50 mcg of selenium and 50 mcg of molybdenum per veggie cap, amounts that are at or close to the Recommended Daily Intake for these trace minerals. Although these minerals help to convert glutathione (derived downstream from the NAC) into its more active form, these are not necessary from a supplement since most people get these amounts in their normal diet. (See the Encyclopedia article and the CL Answer on molybdenum for more information about this mineral). If you just want NAC from a capsule, you actually have to pay a bit more: Our Top Pick in this case is Life Extension N-Acetyl-L-Cysteine, providing 600 mg NAC in a 15-cent vegetarian capsule.

Tablet: NOW NAC provides 1,000 mg of NAC per large tablet for just 9 cents -- a very low cost for NAC, and fine if you don't need to take a lower dose.

PharmaNAC — Pink Berry Blast effervescent tablets were the most expensive way to get NAC (94 cents per 900 mg tablet). Although not a Top Pick, these may be preferable for people who have trouble swallowing pills and don't want to deal with powders, as they rapidly dissolve in water, making a pleasant tasting drink. If you watch your sodium intake, be aware that each tablet contains 200 mg of sodium, so the suggested daily serving of two tablets adds 400 mg of sodium to your diet.

Test Results by Product:
Listed below are the test results for eleven NAC supplements. Eight products were selected by and three others (each denoted with a CL flask) are included for having passed the same evaluation through the Quality Certification Program.

Also shown are the amounts of NAC and serving sizes as listed on the product labels. Products listed as "Approved" met their label claim for NAC and's quality criteria (see Passing Score). The full list of ingredients is available for each product by clicking on the word "Ingredients" in the first column, although some notable features are listed in the last column as are price and cost comparisons.

Click on beneath a product name to find a vendor that sells it.
To find retailers that sell some of the listed products click here.
Product Name, Listed Amount of NAC per Unit, Serving Size, and Suggested Daily Serving on Label

Click on "Ingredients" for Full Listing
Claimed Amount NAC Per Labeled Daily Serving --TEST RESULTS--

(See How Products Were Evaluated)
Cost For Daily Suggested Serving On Label

[Cost per 600 mg NAC]

Other Notable Features1

Price Paid

Contained Labeled Amount of NAC Disintegrated Properly

NA = Not Applicable
Carlson NAC (500 mg per capsule; 1 capsule, once to three times daily)

Dist. by Carlson Division of J.R. Carlson Laboratories, Inc.
500 mg to 1,500 mg

Large capsule
APPROVED NA $0.16-$0.48



$9.59/60 capsules

Doctor's Best® NAC Detox Regulators with Seleno Excell® (600 mg per veggie cap; 1 veggie cap, once to four times daily2)

Dist. by Doctor's Best, Inc.
600 mg to 2,400 mg

Large veggie cap
APPROVED NA $0.10-$0.41

Lowest cost for NAC from a (vegetarian) capsule

Selenium (50-200 mcg), molybdenum (50-200 mcg)

Suitable for vegetarians, non-GMO, gluten free

$6.20/60 veggie caps
GNC NAC (600 mg per capsule; 1 capsule, once to twice daily)

Dist. by General Nutrition Corporation
600 mg to 1,200 mg

Large capsule
APPROVED NA $0.23-$0.47


No wheat, gluten free, yeast free

$13.99/60 capsules

Life Extension® N-Acetyl-L-Cysteine (600 per vegetarian capsule; 1 vegetarian capsule, once to three times daily)

Dist. by Quality Supplement and Vitamins, Inc.
600 mg to 1,800 mg

Large vegetarian capsule
APPROVED NA $0.15-$0.46



$9.25/06 vegetarian capsules

NOW® NAC (1,000 mg per tablet; 1 tablet, once to three times daily)

Mfd. by Now Foods
1,000 mg to 3,000 mg

Large tablet
APPROVED $0.09-$0.28

Lowest cost for NAC from a pill

Kosher, non-GMO, not manufactured with wheat and gluten

$11.00/120 tablets
NutraBio® NAC (1 scoop [600 mg]; 1 scoop, once to twice daily)

Mfd. by NutraBio Labs, Inc.
600 mg to 1,200 mg

Powder in container
APPROVED NA $0.06-$0.24


Kosher, non-GMO, gluten free

$14.99/5.3 oz [150 g] container (approx. 250 servings)

Nutricost™ NAC (1 scoop [1,200 mg]; 1 scoop, no recommended daily serving size)

Dist. by Nutricost
1,200 mg3

Powder in container

Lowest cost for NAC

Non-GMO, gluten free

$18.45/0.55 lbs [250 g] container (approx. 208 servings)
PharmaNAC® -Pink Berry Blast (900 mg per effervescent tablet; 1 effervescent tablet, twice daily)

Dist. by Bioadvantex Pharma Inc.
1,800 mg (Thiolex®)

Large circular effervescent tablet


Sodium (400 mg)

Gluten free

$22.50/24 effervescent tablet
Seeking Health® NAC (500 mg per vegetarian capsule; 1 vegetarian capsule, no recommended daily serving size)

Dist. by Seeking Health, LLC
500 mg3

Large vegetarian capsule


Does not contain wheat

$21.95/90 vegetarian capsules
Solgar® NAC 600 mg (600 mg per vegetable capsule; 1 vegetable capsule, once

Mfd. by Solgar, Inc.
600 mg to 1,200 mg

Large vegetable capsule
APPROVED NA $0.33-$0.66


Kosher, suitable for vegans, non-GMO, free of wheat, gluten and yeast

$39.70/120 vegetable capsules
Vital Nutrients NAC (600 mg per vegetarian capsule; 1 to 2 vegetarian capsules, once to twice daily4)

Mfd. by Vital Nutrients
600 mg to 2,400 mg

Large vegetarian capsule
APPROVED NA $0.33-$1.32


Excludes wheat and gluten

$32.90/100 vegetarian capsules
Tested through CL's Quality Certification Program prior to, or after initial posting of this Product Review.

1 Not tested but claimed on label.
2 Label states "Take 1 capsule daily, preferably with a meal. For additional detoxification support take up to 4 capsules daily, or as recommended by a nutritionally-informed physician."
3 Based on 1 serving daily.
4 Label states "1 or 2 capsules 1-2 times daily with food, or as directed by your healthcare professional."
Unless otherwise noted, information about the products listed above is based on the samples purchased by (CL) for this Product Review. Manufacturers may change ingredients and label information at any time, so be sure to check labels carefully when evaluating the products you use or buy. If a product's ingredients differ from what is listed above, it may not necessarily be of the same quality as what was tested.

The information contained in this report is based on the compilation and review of information from product labeling and analytic testing. CL applies what it believes to be the most appropriate testing methods and standards. The information in this report does not reflect the opinion or recommendation of CL, its officers or employees. CL cannot assure the accuracy of information.
Copyright, LLC, 2019. All rights reserved. Not to be reproduced, excerpted, or cited in any fashion without the express written permission of LLC.


What to Consider When Buying:

There are a number of things to look for when choosing a NAC product. First, don't be put off if you notice a slight smell of sulfur, like that of cooked eggs. Unless a product is coated or wrapped, you will notice this odor with most products. This is normal and does not typically indicate spoilage or contamination.

If you purchase a powder, store it in the closed container in a cool, dry place — away from excessive heat or moisture (refrigeration is not necessary and could potentially expose the powder to moisture once the container has been opened). NAC is quite stable and can be stored for at least 2 months this way without spoiling or degrading. When stored for longer periods of times (several months to years) small amounts of NAC may degrade into di-NAC, which is not known to be harmful and has actually been shown, in preliminary studies, to have an anti-atherosclerotic effect, perhaps through modulation of the immune system (Pettersson, Cardiovasc Drug Rev 2003).

As noted earlier, the Supplement Facts panels on products may list "free form" after listing NAC. This means that the NAC is not combined with a salt or another stabilizer. However, as mentioned above, NAC is quite stable, and as our tests found, all NAC supplements contain the "free form." So even if you don't see it listed on the label as such, your supplement will likely contain "free form" NAC.

As discussed above, the dose of NAC used in clinical trials has ranged from about 600 mg to 3,000 mg per day, typically divided into two or three servings. See the What It Does section for the dosage for specific uses.

NAC may be taken with or without food. However, as noted in Cautions and Concerns section below, higher doses of NAC can cause stomach upset. If this is the case, taking it with food may help.

Concerns and Cautions:
NAC is generally well tolerated. However, some people may experience headache or gastrointestinal symptoms such as nausea, abdominal pain, vomiting, constipation, and diarrhea when taking higher doses (1,200 mg or more per day).

NAC should not be taken with nitroglycerine except under physician supervision, as this can cause severe headaches and an unsafe lowering of blood pressure.

People with asthma should be aware that NAC has been alleged to worsen asthma (Grant, JAMA Psych, 2016).

Women who are pregnant or nursing should not take NAC unless directed by their physician.

NAC can interfere with results of blood tests for cholesterol (including HDL-cholesterol) and uric acid, showing falsely low results, but this effect is mainly of concern when large doses (several thousand milligrams) are given within 12 hours before blood draw, such as when NAC is given intravenously to treat acetaminophen overdose (Genzen, Clin Biochem 2016). It is very unlikely that typical oral doses of NAC will cause interference but, to eliminate the chance of interference, you can avoid taking NAC within a day before blood tests.

To further assist consumers, licenses its flask-shaped CL Seal of Approved Quality (see The CL Seal) to manufacturers for use on labels of products that have passed its testing. will periodically re-evaluate these products to ensure their compliance with's standards.

Information on this site is provided for informational purposes only. It is not an endorsement of any product nor it is it meant to substitute for the advice provided by physicians or other healthcare professionals. The information contained herein should not be used for diagnosing or treating a health problem or disease.
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