NAC for Fertility: What the Evidence Shows

Fertility Health Guides and Reproductive Health Research NAC (N-Acetylcysteine) for Fertility: What the Evidence Shows

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NAC (N-acetylcysteine) is a form of the amino acid cysteine that has been tested in fertility trials, most of them small, mainly in women with polycystic ovary syndrome (PCOS) and in men with abnormal semen test results. A 2015 review of 8 trials in 910 women with PCOS found more ovulation and more pregnancies with NAC than with a dummy pill (placebo), but fewer than with metformin, a diabetes medicine that is also used in PCOS.1

If you're trying to conceive and have seen NAC suggested online, the evidence is thinner than it first looks. Most of the trials are small, and the only trial in that review to report live births has since been retracted by its journal.1,4 NAC also has no authorised health claim in Great Britain, which means no food or supplement label or advert may say it has a health benefit.2

KEY TAKEAWAYS
  • A 2015 review of 8 trials in 910 women with PCOS found more ovulation and pregnancies with NAC than with placebo, and fewer than with metformin.1
  • The only trial in that review to measure live births was retracted in 2025, so that review has no reliable live birth result for NAC in PCOS, and its pregnancy figure partly rests on that trial.1,4
  • In men, reviews of a few trials report higher readings on some semen measures with NAC, but they did not measure pregnancies or births.14,15 Both include a trial that now carries an expression of concern, a public warning from the journal that it has doubts about the study.13
  • Trials used 1,200 to 1,800 mg a day in women and 600 mg a day in men.1,12 There is no UK limit for NAC (research level): the UK has set no safe upper amount for NAC as a supplement, so these are simply the doses trials used, not a recommended amount.
  • The UK prescribing information for acetylcysteine warns about narrowing of the airways (bronchospasm), especially in asthma, and an interaction with glyceryl trinitrate (GTN).3
  • NAC has no authorised health claim in Great Britain. Speak to your GP, pharmacist or fertility clinic before using it, especially during fertility treatment.2

What is NAC, and why is it studied for fertility?

NAC is a lab-made form of cysteine, an amino acid the body uses to make glutathione, one of its own antioxidants. Acetylcysteine is the medicine name for the same substance, and in the UK it is also a licensed medicine, for example as 600 mg effervescent tablets used to loosen mucus in chest conditions.3 Fertility researchers study it because of that antioxidant role, not because of any proven fertility benefit.

Oxidative stress is an imbalance between reactive molecules that can damage cells and the antioxidant defences that mop them up. Researchers think it may play a part in some cases of subfertility in women and in men, which is why antioxidants are tested in fertility trials.7,16 A plausible mechanism in the lab is not the same as a trial showing more pregnancies, so the rest of this guide looks at what the trials in people actually found, and what that might mean for you.

On food and supplement labels in Great Britain, only health claims listed on the GB Nutrition and Health Claims Register may be used. The register lists a claim linking NAC to glutathione as non-authorised, and a claim that a combination product containing NAC reduced sperm DNA damage was also rejected.2

Section Summary: NAC is an antioxidant compound that is also a licensed UK medicine for chest conditions. It has no authorised fertility or health claim in Great Britain.

What does the research show for NAC and PCOS?

A 2015 review of 8 randomised trials in 910 women with PCOS found that women taking NAC were more likely to ovulate and become pregnant than women taking placebo, but less likely than women taking metformin.1 The reviewers rated several trials at high risk of bias and asked for better trials that measure live births.1

Against placebo, the review found higher odds of pregnancy with NAC (odds ratio 3.58, from 3 trials and 377 women) and higher odds of ovulation (odds ratio 3.13, from 2 trials and 200 women).1 An odds ratio above 1 means the outcome was more common with NAC; it does not mean NAC made pregnancy three times as likely, only that pregnancy was more common with NAC in these trials. One of the three pregnancy trials is the retracted trial described in the next paragraph, so the pregnancy figure is less reliable than it looks. Against metformin, the picture reversed: women taking NAC were less likely to ovulate or become pregnant (2 trials for each outcome).1 Several of these trials gave NAC alongside clomifene, a medicine prescribed to bring on ovulation, so they tested NAC as an add-on to medical treatment rather than a replacement for it.1

The one trial in the review that reported live births, a 2010 Egyptian study of 60 women, was retracted by Reproductive BioMedicine Online in November 2025.1,4 That leaves no reliable live birth figure for NAC in PCOS from this review.

A larger 2023 review of 18 studies with 2,185 participants found that NAC lowered total testosterone and raised follicle stimulating hormone (FSH) in women with PCOS. It found no clear effect on the number of follicles or the thickness of the womb lining.5 Hormone levels are not the same as pregnancies, and that review focused on hormones and ovulation rather than births. It also included at least four trials that have since been retracted, among them the 2010 Egyptian PCOS trial and a 2006 Egyptian trial in unexplained infertility, so its figures partly rest on withdrawn data.4,8,19,20 A 2007 Egyptian trial of NAC with clomifene that it also cites carries a 2021 editor's note from its journal flagging concerns.21

One of the larger recent trials took place at a single hospital in China, with no placebo group and no blinding of the women or their doctors, so its results need careful reading. It added 1,800 mg of NAC a day to ovulation induction (medicines that bring on ovulation, here letrozole tablets and FSH injections) in 230 women with PCOS. Over up to three cycles, 77.9% of women in the NAC group had a clinical pregnancy (a pregnancy seen on an ultrasound scan), compared with 58.0% without NAC, but births were not reported.6 Women were allocated at random, using a computer-generated list in sealed envelopes, but there was no placebo, and the women and their doctors knew who was taking NAC.6

If you have PCOS and hoped for a clear answer, the evidence here is frustratingly tangled. Your GP or clinic can talk it through with you.

The NHS now calls the condition polyendocrine metabolic ovarian syndrome (PMOS); this guide uses PCOS because that is the name in the studies. The medicines the NHS lists for PMOS include clomifene, to help with fertility, and metformin; NAC is not among them.17 Our guide to PCOS and fertility covers the condition itself.

Section Summary: In trials, women with PCOS who took NAC had more ovulations and pregnancies than with placebo, but fewer than with metformin. The evidence is low quality, and none of the trials described here gives a reliable live birth result.

Does NAC help with unexplained infertility or IVF?

There is very little reliable evidence either way. An Egyptian trial of NAC with clomifene in 804 women with unexplained infertility, which found no benefit, was retracted in 2023.8 In IVF and ICSI (where a single sperm is injected into an egg), small trials have looked at egg and embryo measures, and those that measured pregnancy found no clear difference.9,10

An Egyptian trial of 76 women having ICSI because of a sperm problem found clinical pregnancy in 52.6% of women given NAC and 47.4% of those who were not, a difference too small to rule out chance.9 A Chinese trial of 200 older women (average age about 38) having IVF or ICSI compared about 45 days of NAC with no NAC. The NAC group needed lower doses of the hormone injections used to stimulate the ovaries, and slightly more of their blastocysts (embryos five or six days old) were rated high quality, but clinical pregnancy rates did not differ.10 A pilot trial of 60 women with PCOS having ICSI was split into four groups of 15 (NAC, metformin, both, or placebo). Compared with placebo, it reported fewer immature eggs and more embryos graded good with 1,800 mg of NAC a day. Its published summary did not report pregnancy rates.11

The 2020 Cochrane review of antioxidants for female subfertility, which included NAC trials, rated the evidence low to very low quality and concluded there was limited evidence for antioxidants in subfertile women.7 In March 2026 Cochrane added a note that seven of its included studies have since been retracted and two more carry expressions of concern, although the editors judged its overall conclusions unchanged.7

If you're having IVF or ICSI, tell your clinic about any supplement before you start, so they know everything you're taking during treatment.

Section Summary: Trials of NAC during IVF and ICSI are few and small, and those that measured pregnancy found no clear difference. A large trial of NAC in unexplained infertility has been retracted.

What does the research show for NAC in men?

Reviews of a few trials in men with unexplained infertility or abnormal semen results report higher semen volume, sperm concentration and sperm motility (movement) with NAC than with placebo.14,15 These are semen test results, not pregnancies or births, and there are only a handful of trials.

A 2021 review pooled 3 randomised trials with 431 men, counting only the NAC and placebo groups of the larger Iranian trial described below. It found higher sperm concentration, semen volume, motility and share of normally shaped sperm with NAC than with placebo, but no difference in testosterone or other hormones.14 A 2025 review of 5 studies reported similar semen findings and said the trials it included did not report any side effects.15 Both reviews drew on the Iranian trial of 468 men that now carries an expression of concern (described below), so their figures partly rest on a study the journal has flagged.13,14,15

The individual trials show the limits. In a Turkish trial of 120 men given 600 mg a day for three months, semen volume and motility were higher than with placebo, but sperm count and shape were not.12 The largest NAC trial in men, an Iranian study of 468 men published in 2009, now carries an expression of concern from the Journal of Urology, which means the journal has publicly flagged doubts about it.13

The 2022 Cochrane review of antioxidants for male subfertility looked at many different antioxidants together. It found very low certainty evidence that they might increase live births, and no clear effect once trials at high risk of bias were removed.16 It also found that antioxidants may cause more mild stomach discomfort than placebo.16

If you'd like to know what those semen numbers mean, our guide to normal semen analysis results explains each one, and the male fertility guide covers causes and tests.

Section Summary: In a handful of trials, men taking NAC had higher readings on some semen measures than men taking placebo, but the reviews looked at semen results rather than pregnancies or births. The largest trial carries an expression of concern.

How much NAC was used in fertility trials?

Trials in women with PCOS used 1,200 to 1,800 mg of NAC a day, often split into two or three doses, and trials in men used 600 mg a day for three to six months.1,12,13 There is no UK limit for NAC (research level): the UK has not set a safe upper amount for NAC as a supplement, so the figures below are doses used in research, not a recommended amount.

Doses of NAC used in fertility trials

Who was studied Dose used in trials How long
Women with PCOS (8 trials in the 2015 review) 1,200 to 1,800 mg a day Varied between trials1
Women with PCOS having ovulation induction 1,800 mg a day Up to three treatment cycles6
Women with PCOS having ICSI 1,800 mg a day About six weeks11
Men with unexplained infertility (Turkey) 600 mg a day Three months12
Men with low sperm measures (Iran, expression of concern) 600 mg a day 26 weeks13

For comparison, the UK licensed 600 mg acetylcysteine tablet for chest conditions is taken once a day, so the doses used in the women's trials were two to three times that amount.3 The trial doses above are doses used in research, not advice on how much to take.

What are the side effects, and who should take care?

In the PCOS trials, side effects were reported as mild, though often not described in detail.1 The UK prescribing information (summary of product characteristics) for 600 mg acetylcysteine lists stomach upset, headache and allergic reactions, and warns that it can cause narrowing of the airways (bronchospasm), especially in people with asthma.3

The same document gives these cautions:3

  • Asthma: stop taking it straight away if bronchospasm happens.
  • Stomach ulcers: take care if you have had a peptic ulcer.
  • Glyceryl trinitrate (GTN): acetylcysteine may increase the blood vessel widening effect of this chest pain medicine, so caution is advised.
  • Antibiotics and cough medicines: take antibiotics two hours before or after it, and do not take it with cough suppressants.
  • Activated charcoal: can reduce how much acetylcysteine your body absorbs.
  • Blood clotting: studies show acetylcysteine reduces how platelets (the blood cells that help clotting) clump together, and the clinical significance of this is not known.
  • Skin reactions: very rare serious skin reactions have been reported, usually alongside another medicine.

If you take any prescribed medicine, including a blood thinner, have asthma, or are having fertility treatment, speak to your GP, pharmacist or fertility clinic before taking NAC.

Can you take NAC during pregnancy or breastfeeding?

The evidence is limited. The UK prescribing information for the 600 mg medicine says there are limited data on acetylcysteine in pregnant women, that it crosses the placenta, and that available data do not indicate a risk to the baby.3 Fertility trials were not designed to test NAC in pregnancy, so this question is still open.

The same document says it is not known whether acetylcysteine passes into breast milk, although no effects on the baby are expected at medicine doses.3 That advice is for a licensed medicine taken for a medical reason, not for a supplement taken in the hope of conceiving. If you become pregnant while taking NAC, or are breastfeeding, ask your GP, midwife or pharmacist whether to carry on.

When should you see a GP about fertility?

If you haven't seen a GP yet, the NHS advises going if you have not conceived after a year of trying. It advises going sooner if you are a woman aged 36 or over or already know you may have a fertility problem.18 A GP can check for common causes of fertility problems and suggest treatments that could help.18

If this feels like a lot to weigh up, you don't have to decide on your own.

Taking a supplement should never delay that conversation, and if you are already seeing a fertility clinic, take any questions about NAC to them. The NHS also advises seeing a GP if you think you might have PMOS (the new NHS name for PCOS), whatever you decide about NAC.17

Frequently Asked Questions

Can NAC help you get pregnant?

In trials of women with PCOS, NAC was linked with more pregnancies than placebo but fewer than metformin, and the evidence is low quality.1 Its only trial to report live births, which also counted towards the pregnancy figure, has since been retracted,4 so there is no reliable live birth result. Talk to your GP or fertility clinic before relying on NAC.

How much NAC is used for fertility?

Trials in women with PCOS used 1,200 to 1,800 mg a day, and trials in men used 600 mg a day for three to six months.1,12,13 These are doses used in research, not a recommended amount. There is no UK limit for NAC (research level), meaning no official safe upper amount has been set, so speak to your GP or pharmacist before trying it.

What does the research say about NAC and eggs?

A pilot trial of 60 women with PCOS having ICSI reported fewer immature eggs with NAC, and a trial of 200 older women having IVF or ICSI reported slightly more blastocysts rated high quality.10,11 The trial that measured pregnancy found no difference.10 Lab measures of eggs and embryos do not tell you whether a supplement leads to a baby.

Is NAC or CoQ10 better for fertility?

We did not find a trial comparing NAC with coenzyme Q10 (CoQ10) head to head, so there is no fair way to say one is better. Both have been studied as antioxidants in fertility, mostly in small trials. Neither has an authorised health claim in Great Britain, and the GB register lists claims for both as non-authorised.2

Can men take NAC for sperm?

Trials gave men 600 mg of NAC a day for three to six months and reported higher readings on some semen measures than placebo.12,14 The reviews did not measure pregnancies or births, and the largest trial carries an expression of concern.13 If you're thinking of trying it, check with your GP or pharmacist first, especially if you take other medicines.

Should I stop NAC if I get pregnant?

Ask your GP, midwife or pharmacist. The UK prescribing information for the 600 mg acetylcysteine medicine says data in pregnancy are limited, although available data do not indicate a risk to the baby.3 Fertility trials were not designed to test NAC in pregnancy, so it is sensible to get advice rather than carry on by default.

Who should not take NAC?

The UK prescribing information for acetylcysteine says not to take it if you are allergic to it, and advises caution if you have asthma, because it can cause bronchospasm, or have had a stomach ulcer.3 It can also interact with glyceryl trinitrate (GTN) and some other medicines. Check with a pharmacist if you take any regular medicine.

Related Reading

References

  1. Thakker D, Raval A, Patel I, Walia R. N-acetylcysteine for polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled clinical trials. Obstetrics and Gynecology International. 2015;2015:817849. doi:10.1155/2015/817849
  2. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register (spreadsheet updated 19 May 2026; entries for N-acetyl-L-cysteine, the NAC-containing combination product Condensyl and coenzyme Q10, all non-authorised). https://www.gov.uk/government/publications/great-britain-nutrition-and-health-claims-nhc-register. Accessed 6 October 2026.
  3. Alturix Ltd. NACSYS 600 mg effervescent tablets (acetylcysteine): summary of product characteristics. Electronic Medicines Compendium. Text revised 12 July 2023. https://www.medicines.org.uk/emc/product/8576/smpc. Accessed 6 October 2026.
  4. Retraction notice to "Effect of N-acetyl-cysteine after ovarian drilling in clomiphene citrate-resistant PCOS women: a pilot study" (Nasr A, 2010;20(3):403-409). Reproductive BioMedicine Online. 2025;51(5):105286. doi:10.1016/j.rbmo.2025.105286
  5. Shahveghar Asl Z, Parastouei K, Eskandari E. The effects of N-acetylcysteine on ovulation and sex hormones profile in women with polycystic ovary syndrome: a systematic review and meta-analysis. British Journal of Nutrition. 2023;130(2):202-210. doi:10.1017/S0007114522003270
  6. Fang YQ, Ding H, Li T, Zhao XJ, Luo D, Liu Y, Li Y. N-acetylcysteine supplementation improves endocrine-metabolism profiles and ovulation induction efficacy in polycystic ovary syndrome. Journal of Ovarian Research. 2024;17(1):205. doi:10.1186/s13048-024-01528-8
  7. Showell MG, Mackenzie-Proctor R, Jordan V, Hart RJ. Antioxidants for female subfertility. Cochrane Database of Systematic Reviews. 2020;8(8):CD007807 (editorial note added 5 March 2026). doi:10.1002/14651858.CD007807.pub4
  8. Retraction notice to "Clomiphene citrate plus N-acetyl cysteine versus clomiphene citrate for augmenting ovulation in the management of unexplained infertility: a randomized double-blind controlled trial" (Badawy A, El Nashar AB, El Totongy M, 2006;86(3):647-650). Fertility and Sterility. 2023;120(2):395. doi:10.1016/j.fertnstert.2023.06.016
  9. Elgindy EA, El-Huseiny AM, Mostafa MI, Gaballah AM, Ahmed TA. N-acetyl cysteine: could it be an effective adjuvant therapy in ICSI cycles? A preliminary study. Reproductive BioMedicine Online. 2010;20(6):789-796. doi:10.1016/j.rbmo.2010.03.001
  10. Li X, Wang Z, Wang H, Xu H, Sheng Y, Lian F. Role of N-acetylcysteine treatment in women with advanced age undergoing IVF/ICSI cycles: a prospective study. Frontiers in Medicine. 2022;9:917146. doi:10.3389/fmed.2022.917146
  11. Cheraghi E, Mehranjani MS, Shariatzadeh MA, Esfahani MH, Ebrahimi Z. N-acetylcysteine improves oocyte and embryo quality in polycystic ovary syndrome patients undergoing intracytoplasmic sperm injection: an alternative to metformin. Reproduction, Fertility and Development. 2016;28(6):723-731. doi:10.1071/RD14182
  12. Ciftci H, Verit A, Savas M, Yeni E, Erel O. Effects of N-acetylcysteine on semen parameters and oxidative/antioxidant status. Urology. 2009;74(1):73-76. doi:10.1016/j.urology.2009.02.034
  13. Safarinejad MR, Safarinejad S. Efficacy of selenium and/or N-acetyl-cysteine for improving semen parameters in infertile men: a double-blind, placebo controlled, randomized study. Journal of Urology. 2009;181(2):741-751. doi:10.1016/j.juro.2008.10.015. Expression of concern: Journal of Urology. 2023. doi:10.1097/JU.0000000000003113
  14. Zhou Z, Cui Y, Zhang X, Zhang Y. The role of N-acetyl-cysteine (NAC) orally daily on the sperm parameters and serum hormones in idiopathic infertile men: a systematic review and meta-analysis of randomised controlled trials. Andrologia. 2021;53(2):e13953. doi:10.1111/and.13953
  15. Syarif S, Makkaraka MAG, Zainal ATF, Birowo P, Atmoko W. Unlocking the potential of antioxidant supplementation with n-acetylcysteine to improve seminal parameters and analysis of its safety: a systematic review and meta-analysis of randomized controlled trials. Archivio Italiano di Urologia e Andrologia. 2025;97(1):13750. doi:10.4081/aiua.2025.13750
  16. de Ligny W, Smits RM, Mackenzie-Proctor R, Jordan V, Fleischer K, de Bruin JP, Showell MG. Antioxidants for male subfertility. Cochrane Database of Systematic Reviews. 2022;5(5):CD007411. doi:10.1002/14651858.CD007411.pub5
  17. National Health Service (NHS). Polyendocrine metabolic ovarian syndrome (PMOS): overview and treatment. Page last reviewed 30 June 2026. https://www.nhs.uk/conditions/polyendocrine-metabolic-ovarian-syndrome-pmos/. Accessed 6 October 2026.
  18. National Health Service (NHS). Infertility. Page last reviewed 9 August 2023. https://www.nhs.uk/conditions/infertility/. Accessed 6 October 2026.
  19. Statement of retraction: "The adjuvant effect of metformin and N-acetylcysteine to clomiphene citrate in induction of ovulation in patients with polycystic ovary syndrome" (Maged AM, Elsawah H, Abdelhafez A, et al., 2015;31(8):635-638). Gynecological Endocrinology. 2025. doi:10.1080/09513590.2025.2600208
  20. Retraction: "Randomized controlled trial of N-acetylcysteine versus l-carnitine among women with clomiphene-citrate-resistant polycystic ovary syndrome" (El Sharkwy IA, Abd El Aziz WM, 2019;147(1):59-64). International Journal of Gynecology and Obstetrics. 2023. doi:10.1002/ijgo.14995
  21. Editor's Note: "N-Acetyl cysteine and clomiphene citrate for induction of ovulation in polycystic ovary syndrome: a cross-over trial" (Badawy A, State O, Abdelgawad S, 2007;86(2):218-222). Acta Obstetricia et Gynecologica Scandinavica. 2021;100:2126. doi:10.1111/aogs.14194
Marina Carter, Health and Fertility Writer

Marina Carter

Health & Fertility Writer

Marina Carter is FertilitySmart's lead writer on fertility, preconception health, and reproductive nutrition. She translates the clinical and nutritional evidence base into honest, practical guidance for individuals and couples trying to conceive, working closely with the product team to ensure every article reflects current peer-reviewed research and the lived emotional reality of the fertility journey. Read Full Bio →

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