Product Reviews
N-Acetyl Cysteine Supplements Review

Initial Posting: 9/27/14 Last Update: 12/4/17 N-acetyl cysteine (NAC) supplements tested by

Sections: Jump to a section by clicking on its name. 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, and in combination with nitroglycerine, to treat angina. 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). 

As a supplement, NAC may help to reduce flu symptoms and severity, although it has not been shown to reduce the occurrence of flu infection. One placebo-controlled clinical study found 600 mg of NAC taken twice daily during flu season (October — April) significantly reduced 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.

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).

Although NAC is used treat acetaminophen overdose (it helps to replenish glutathione in the liver which is depleted by high doses of acetaminophen), no studies in people have evaluated the effects of taking NAC with acetaminophen to prevent acetaminophen-related liver damage. 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). 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).

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 of the NAC supplements that selected for review passed testing, as did four supplements tested through's Quality Certification Program.

Choosing an NAC supplement — and getting best value
Most of the products tested provided 500 mg or 600 mg of NAC per pill (capsule, tablet, caplet), although one (Nature's Answer) provided 300 mg, and an effervescent tablet (PharmaNAC) provided 900 mg. The total suggested daily serving sizes ranged from one to three pills per day, yielding 500 mg to 1,800 mg of NAC. These amounts are generally in line with what has been used in clinical studies.

In the Supplements Facts panels on the products, some listed the amount of NAC in "free form" while other did not. With some supplement ingredients which are stabilized with various types of salt, 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 the products all contained the listed amounts of NAC and there were no problems with tablet/caplet disintegration, you may want to choose a product based on price and other special features or ingredients of importance. In terms of price alone, we calculated the cost to get an equivalent amount of NAC (600 mg) from each product, as shown in brackets in the last column of the table below. We found the lowest cost was just 9 cents from either Doctor's Best Best NAC Detox Regulators or Puritan's Pride NAC N-Acetyl Cysteine. Both are gluten-free. Doctor's Best includes some selenium and molybdenum (50 mcg of each, which is at or close to the Recommended Daily Intake for these trace minerals). Although these minerals help to convert the 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).

KAL NAC+ (18 cents per 600 mg) also includes molybdenum at an even higher, but safe, dose (150 mcg). KAL NAC+ also includes 10 mg of riboflavin which, like selenium and molybdenum, helps to convert glutathione to its more active form, and a very small amount of calcium (7 mg calcium carbonate), which may simply be part of the formulation to help the tablet disintegrate more quickly.

The PharmaNAC — Wildberry effervescent tablets were the most expensive way to get NAC (70 cents per 600 mg — or $1.05 per 900 mg tablet). They may be preferable for people who have trouble swallowing pills, as they rapidly dissolve in water and making a pleasant tasting drink, but, if you need watch your sodium intake, be aware that each table also contains 200 mg of sodium. 

Test Results by Product:
Listed below are the test results for fourteen NAC supplements. Ten products were selected by and four others (each denoted with a CL flask) are included for having passed the same evaluation through the Quality Certification Program. Also listed is one product very similar to one which was Approved in testing but is sold under a different brand name.

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, Serving Size, and Suggested Daily Serving on Label

Click on "Ingredients" for Full Listing
Claimed Amounts and Forms of NAC Per Daily Serving --TEST RESULTS-- Cost of Daily Suggested Serving on Label

[Cost of 600 mg of NAC]

Other Notable Features1

Price Paid

Contained Listed Amount of NAC Disinte-grated Properly

(NA = Not Applicable)
Bluebonnet NAC (500 mg per Vcap®; 1 Vcap®, once daily)

Mfd. by Bluebonnet Nutrition Corporation
500 mg free-form APPROVED NA $0.27


Kosher, suitable for vegans, free of wheat, gluten and yeast

$23.96/90 Vcaps®  
Carlson® NAC (500 mg per capsule; 1 capsule, once to three times daily)

Dist. by Carlson Division of J.R. Carlson Laboratories, Inc.
500 to 1,500 mg
APPROVED NA $0.17-$0.50


Wheat free, yeast free

$10.08/60 capsules
Doctor's Best® Best NAC Detox Regulators (600 mg per veggie cap; 1 veggie cap, once to four times daily)

Dist. by Doctor's Best Inc.
600 to 2,400 mg
APPROVED NA $0.09-$0.35

Lowest cost for NAC

Selenium, molybdenum

Suitable for vegans, non-GMO, gluten free

$5.18/60 veggie caps
KAL® NAC+ (600 mg per tablet; 1 tablet, once daily)

Mfd. by Nutraceutical Corp.
600 mg


Riboflavin, calcium, molybdenum

$11.09/60 tablets
Nature's Sunshine® N-Acetyl Cysteine (300 mg per tablet; 1 tablet, twice daily)

Dist. by Nature's Sunshine Product, Inc.
600 mg


$15.50/60 tablets
NutriCology® NAC (500 mg per tablet; 1 tablet, once to three times daily)

Dist. by NutriCology®
500 to 1,500 mg
APPROVED $0.24-$0.72



$28.99/120 tablets
PharmaNAC® - Wildberry (900 mg per effervescent tablet; 1 effervescent tablet, twice daily)

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



Gluten free

$33.60/32 effervescent tablets  
Pure Encapsulations® NAC (600 mg per capsule; 1 capsule, three times daily)

Dist. by Pure Encapsulations, Inc.
1,800 mg


Ascorbyl Palmitate (fat-soluble vitamin C)


$45.30/180 capsules  
Puritan's Pride® NAC N-Acetyl Cysteine (600 mg per capsule; 1 capsule, once to twice daily)

Manufactured by Puritan's Pride
600 to 1,200 mg
APPROVED NA $0.09-$0.173  

Lowest cost for NAC

No wheat, gluten and yeast

$10.33/120 capsules3
Solgar® NAC 600 mg (600 mg per vegetable capsule; 1 vegetable capsule, once to twice daily)

Mfd. by Solgar, Inc.
600 to 1,200 mg
APPROVED NA $0.49-$0.99


Kosher, suitable for vegetarians, free of wheat, gluten and yeast

$29.67/60 vegetable capsules
Source Naturals® N-Acetyl Cysteine (600 mg per tablet; 1 tablet, once to three times daily)

Dist. by Source Naturals, Inc.
600 to 1,200 mg
APPROVED $0.11-$0.34


Contains no wheat, gluten and yeast, hypo-allergenic

$13.58/120 tablets
Twinlab® NAC Fuel™ (600 mg per capsule; 1 capsule, once to twice daily)

Mfd. by Twinlab Corporation
600 to 1,200 mg
APPROVED NA $0.14-$0.29


Does not contain wheat, gluten and yeast

$12.99/90 capsules
The Vitamin Shoppe® NAC (600 mg per capsule; 1 capsule, once daily)

Dist. by Vitamin Shoppe, Inc.
600 mg


Does not contain wheat, gluten and yeast

$29.99/200 capsules
Whole Foods™ NAC (500 mg per capsule; 1 capsule, once to three times daily)

Dist. by Whole Foods Market
500 to 1,500 mg
APPROVED NA $0.15-$0.45


$14.99/100 capsules
Similar to Approved Products*:
Vitamin World NAC N-Acetyl Cysteine (600 mg per capsule; 1 capsule, once to twice daily)

Mfd. by Vitamin World, Inc.
Similar to Puritan's Pride® NAC N-Acetyl Cysteine.

Tested through CL's Quality Certification Program prior to, or after initial posting of this Product Review.

* Product identical in formulation and manufacture to a product that has passed testing but sold under a different brand. For more information see CL's Multi-Label Testing Program.

1 Not tested but claimed on label.
2 Form not stated on label. From the results from the laboratory used, it is assumed that the product is a free-form of NAC.
3 Purchased at promotional pricing: "Buy 1, get 2 free." Paid $30.99 for 3 bottles.

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, 2014. 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 an NAC product. First, don't be put off if you notice a 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.

In addition to tablets and capsules, NAC can be purchased in bulk as a loose powder. The powder should be stored in a 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).

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 grams) 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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