N-Acetylcysteine (NAC)
Research reviewed: Up until 03/2026
N-Acetylcysteine (NAC) is a dietary supplement with 9 published peer-reviewed studies involving 1,904 participants, researched for Antioxidant, Fertility, Respiratory Health.
Evidence at a Glance
Strength is scored by study design, sample size, study type, and outcomes
Antioxidant
ModerateFertility
StrongRespiratory Health
StrongResearch Visualised
Visual breakdown of the clinical data.
Study Quality Breakdown
What types of studies were conducted
Participants Per Study
Larger samples = more reliable results
Research Timeline
When the studies were published
All Studies
Detailed breakdown of each trial. Click to expand.
Antioxidant
To evaluate the antioxidant effects of NAC on composite cardiovascular end points (heart attacks, strokes, cardiovascular deaths, and peripheral vascular events) in patients undergoing hemodialysis
Study Type
Prospective, randomised, placebo-controlled trial
Purpose
To evaluate the antioxidant effects of NAC on composite cardiovascular end points (heart attacks, strokes, cardiovascular deaths, and peripheral vascular events) in patients undergoing hemodialysis
Dose
1.2 g/day acetylcysteine (2 x 600 mg) or placebo
Participants
134 male and female patients with an average age 62 years
Duration
Median (range) follow-up was 14.5 (1 to 24) months
Results
Patients taking acetylcysteine experienced a significantly lower rate of composite cardiovascular events compared to those receiving a placebo. Specifically, 28% (18/64) of patients in the acetylcysteine group had a primary endpoint event, compared to 47% (33/70) in the control group. This represents a 40% lower risk for the acetylcysteine group. A primary endpoint was a combined measure of serious cardiovascular issues, including fatal and nonfatal heart attacks, cardiovascular disease-related deaths, the need for procedures like coronary angioplasty (a procedure to widen blocked or narrowed arteries) or bypass surgery, ischemic stroke (a stroke caused by a blood clot), and peripheral vascular disease (a condition affecting blood vessels outside of the heart and brain) requiring amputation or angioplasty
To assess the effects of oral NAC in reducing total antioxidant capacity as a measure of oxidative stress in chronic hemodialysis patients.
Study Type
Randomised controlled clinical trial
Purpose
To assess the effects of oral NAC in reducing total antioxidant capacity as a measure of oxidative stress in chronic hemodialysis patients.
Dose
1.2 g/day acetylcysteine (2 x 600 mg tablets) or placebo
Participants
40 male and female chronic hemodialysis patients with an average age of 43 years
Duration
6 weeks
Results
Researchers observed that in the NAC group, average total antioxidant capacity increased significantly from 26.39 to 33.26 (approximately 26% boost in total antioxidant protection) while in the placebo group, the increase was non-significant. No major adverse effects observed.
To determine the effects of oral NAC on malondialdehyde levels (a lipid peroxidation marker measuring how much oxidative damage is occurring to fats in the blood) in chronic hemodialysis patients.
Study Type
Pilot Study
Purpose
To determine the effects of oral NAC on malondialdehyde levels (a lipid peroxidation marker measuring how much oxidative damage is occurring to fats in the blood) in chronic hemodialysis patients.
Dose
1.2 g/day acetylcysteine (2 x 600 mg tablets) or control (no treatment)
Participants
24 male and female chronic hemodialysis patients
Duration
30 days
Results
After 30 days, pre-dialysis malondialdehyde (MDA) levels were significantly lower in the NAC group compared to the control group (3.01 vs. 4.5 μmol/L), and post-dialysis levels were also lower (2.76 vs. 4.39 μmol/L). Within the NAC group, MDA dropped significantly from baseline (5.07 → 3.01 μmol/L pre-dialysis; p < 0.002), representing about a 40% reduction in lipid peroxidation. This reduction suggests that NAC supplementation may help decrease oxidative stress—an imbalance between harmful molecules (free radicals) and the body’s ability to neutralize them—which can damage cells and tissues; lipid peroxidation specifically refers to damage to fats in cell membranes caused by these harmful molecules.
Fertility
To examine whether NAC can improve semen quality and oxidative/antioxidant status in men diagnosed with idiopathic infertility (infertility with no identifiable cause, associated with excess reactive oxygen species — unstable molecules that can damage sperm DNA and function).
Study Type
Randomised placebo-controlled trial
Purpose
To examine whether NAC can improve semen quality and oxidative/antioxidant status in men diagnosed with idiopathic infertility (infertility with no identifiable cause, associated with excess reactive oxygen species — unstable molecules that can damage sperm DNA and function).
Dose
600 mg/day NAC or placebo
Participants
120 men with idiopathic infertility (60 in NAC group, 60 in placebo group)
Duration
3 months
Results
The researchers observed that NAC significantly improved semen volume, sperm motility (the percentage of sperm that move properly), and semen viscosity (thickness) compared to placebo. The total antioxidant capacity (the body's overall ability to neutralize damaging molecules) was also significantly higher, while total peroxide (a marker of oxidative damage) and oxidative stress index (a ratio indicating cellular damage) were significantly lower than in the placebo group.
To assess the effects of NAC supplementation on sperm quality, sperm DNA integrity, hormonal profile, and spontaneous pregnancy rate in men with idiopathic infertility (infertility with no identifiable cause, associated with excess reactive oxygen species — unstable molecules that can damage sperm DNA and function).
Study Type
Prospective clinical trial (uncontrolled)
Purpose
To assess the effects of NAC supplementation on sperm quality, sperm DNA integrity, hormonal profile, and spontaneous pregnancy rate in men with idiopathic infertility (infertility with no identifiable cause, associated with excess reactive oxygen species — unstable molecules that can damage sperm DNA and function).
Dose
600 mg/day NAC
Participants
50 infertile men with asthenoteratozoospermia (a condition where sperm have reduced motility and abnormal shape) with an average age of 35 years
Duration
3 months
Results
After 3 months of NAC, the researchers observed that the sperm count and total motility increased significantly. In addition, abnormal sperm morphology (percentage of poorly shaped sperm), DNA fragmentation (breaks in sperm DNA, which reduce fertilization ability), and protamine deficiency (a protein deficiency that destabilizes DNA packaging in sperm) all showed significant decreases). Hormonal improvements included significantly lower FSH (follicle-stimulating hormone, which helps regulate reproductive processes) and LH (luteinizing hormone, which triggers testosterone production) levels, along with higher testosterone (the primary male sex hormone responsible for muscle mass, energy, and reproductive function). Overall, the study showed that NAC significantly improved multiple dimensions of sperm quality — both the structural integrity of sperm DNA and how well sperm move. This suggests NAC may improve the chances of successful fertilization.
To evaluate whether oral NAC, added to clomiphene citrate (a standard drug used to stimulate ovulation), can improve ovulation and pregnancy rates in infertile women with PCOS.
Study Type
Randomised, double-blind, placebo-controlled trial
Purpose
To evaluate whether oral NAC, added to clomiphene citrate (a standard drug used to stimulate ovulation), can improve ovulation and pregnancy rates in infertile women with PCOS.
Dose
NAC 1.2 g/day + clomiphene citrate 100 mg/day (days 3–7 of cycle), or clomiphene + placebo
Participants
180 infertile women with PCOS
Duration
One menstrual cycle with follow-up
Results
The NAC + clomiphene group demonstrated significantly higher ovulation rates and clinical pregnancy rates compared to the clomiphene + placebo group. There was also a trend toward improved endometrial thickness (the lining of the uterus, which must be sufficiently thick for a fertilized egg to implant) in the NAC group.
To determine the effects of NAC supplementation following letrozole/uFSH (fertility drugs) treatment in improving ovulation induction outcomes in women with PCOS. Ovulation induction is a fertility treatment using oral or injectable medications to stimulate the ovaries to develop and release one or more mature eggs, usually in women with irregular or absent ovulation.
Study Type
Pragmatic randomized, parallel-group controlled clinical trial
Purpose
To determine the effects of NAC supplementation following letrozole/uFSH (fertility drugs) treatment in improving ovulation induction outcomes in women with PCOS. Ovulation induction is a fertility treatment using oral or injectable medications to stimulate the ovaries to develop and release one or more mature eggs, usually in women with irregular or absent ovulation.
Dose
1.8 g/day oral NAC (3 x 0.6 g) or control
Participants
230 PCOS women with an average age of 28 years
Duration
Taken from the 2nd to the 4th day of the menstrual cycle for five consecutive days.
Results
The researchers observed that overweight or obese participants who took NAC after fertility treatment showed a significantly higher pregnancy rate, with about 73% becoming pregnant compared to 45% of those who did not (control). This suggests that taking NAC may help increase the chances of becoming pregnant after fertility treatment, especially for women who are overweight or obese.
Respiratory Health
To evaluate whether high-dose N-acetylcysteine (NAC) taken for 1 year can improve lung function and reduce flare-ups in patients with stable Chronic Obstructive Pulmonary Disease (COPD)
Study Type
Randomised, double-blind, placebo-controlled trial
Purpose
To evaluate whether high-dose N-acetylcysteine (NAC) taken for 1 year can improve lung function and reduce flare-ups in patients with stable Chronic Obstructive Pulmonary Disease (COPD)
Dose
1.2 g/day (2 x 600 mg capsules) or placebo
Participants
120 patients with stable COPD with an average age of 71 years
Duration
1 year
Results
The researchers observed that NAC significantly improved air flow from 25%–75%. The number of flare-ups was also significantly reduced: 0.96 per patient per year in the NAC group vs. 1.71 in the placebo group. There was also significant improvement in airway resistance, indicating the airways were less stiff and more open. This suggests that air could move more easily in and out of the lungs, making breathing more efficient and potentially reducing symptoms like shortness of breath and wheezing.
To evaluate whether long-term NAC supplementation reduces the number of flare-ups in patients with moderate-to-severe COPD (Chronic Obstructive Pulmonary Disease)
Study Type
Randomised, double-blind, placebo-controlled trial
Purpose
To evaluate whether long-term NAC supplementation reduces the number of flare-ups in patients with moderate-to-severe COPD (Chronic Obstructive Pulmonary Disease)
Dose
1.2 g/day (2 x 600 mg capsules) or placebo
Participants
1,006 patients with moderate-to-severe COPD, aged 40–80, enrolled at 34 hospitals in China
Duration
1 year
Results
After 1 year, researchers observed that the NAC group had 497 acute flare-ups in 482 patients (1.16 per patient per year) compared to 641 flare-ups in the placebo group (1.49 per patient per year). This difference was statistically significant with a risk ratio=0.78 (95% CI 0.67–0.90; P = 0.0011), meaning patients in the NAC group were about 22% less likely to experience flare-ups compared to those in the placebo group.
Frequently Asked Questions
Common questions about N-Acetylcysteine (NAC) research
There are currently 9 peer-reviewed studies on N-Acetylcysteine (NAC) (N-Acetylcysteine (NAC)), involving 1,904 total participants. Research covers Antioxidant, Fertility, Respiratory Health. The overall evidence strength is rated as Very Strong.
The evidence is currently rated as "Very Strong Evidence". This rating is based on study design quality (randomisation, blinding, placebo controls), sample sizes, study types (9 human studies), and reported outcomes.
N-Acetylcysteine (NAC) has been researched for: Antioxidant, Fertility, Respiratory Health. Each area has its own body of evidence which you can explore in the study breakdowns above.
Yes, 9 out of 9 studies are human trials. Human trials carry more weight in our evidence scoring system.
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