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NAC (N-Acetylcysteine) Supplements: What Trials Show for Lungs, OCD, Fertility and the Liver

NAC (N-acetylcysteine) helps most in chronic bronchitis and COPD: taken by mouth for months, it modestly cut flare-ups in adults (grade B). Added to an SSRI for OCD, results are mixed (grade B, mixed), and one adult trial found less hair pulling (grade C). Two small trials found no change in fatty liver (grade C). With nitroglycerin it can cause severe headache and low blood pressure. A Tylenol overdose is an emergency: call Poison Control.

Published How we grade evidenceEditorial policy

NAC (N-acetylcysteine) is made from cysteine, an amino acid, and your body turns it into glutathione, an antioxidant inside cells. It is also a prescription medicine, used to loosen thick mucus and, in hospital, as the antidote to an acetaminophen (paracetamol, Tylenol) overdose. This guide covers adults taking NAC capsules or tablets by mouth.

A suspected acetaminophen overdose is an emergency. Call 911 or Poison Control at 1-800-222-1222 (US) right away. Hospitals give NAC at doses and times set by blood tests; a supplement at home is no substitute (acetaminophen poisoning consensus).

The short version

  • Chronic bronchitis and COPD (taken by mouth for months, against placebo): modestly fewer flare-ups; newer trials show less benefit than older ones. Grade B (Poole 2019; Cai 2026; Huang 2023).
  • OCD, added to an SSRI in adults (against placebo): lower scores only at 5 to 8 weeks in pooled trials. Grade B, mixed (Eghdami 2024).
  • Hair pulling and skin picking in adults (against placebo): one positive trial each. Grade C (Grant 2009; Grant 2016). In children and teens with hair pulling, no benefit (grade C, Bloch 2013).
  • Fatty liver (MASLD) in adults: no change in liver fat in two small trials, or in liver enzymes in the one that measured them. Grade C (Ramadan 2026; Sinaeinejad 2025).
  • With nitroglycerin (heart patients): oral NAC with a nitroglycerin patch brought more severe headaches, and both given into a vein brought low blood pressure. Grade C for harm (Ardissino 1997; Horowitz 1988).
Question (who, compared with what)What trials foundSize of effectGrade
Flare-ups (adults with COPD, oral NAC vs placebo)Fewer in pooled trials13% lower risk (2,609 people)B
OCD scores (195 adults on SSRIs, add-on vs placebo)Lower at 5 to 8 weeks onlyBorderline (p = 0.05)B, mixed
Hair pulling (50 adults, vs placebo)More people much improved56% vs 16%C
Hair pulling (39 children and teens, vs placebo)No difference25% vs 21% respondedC
Liver fat (60 and 69 adults with MASLD, vs lifestyle advice or placebo)No differenceNo change in either trialC

Does NAC help COPD and chronic bronchitis?

Grade B: a modest drop in flare-ups when taken daily for months. Cochrane reviewers pooled mucus-thinning medicines taken by mouth, NAC among them, across 28 trials (6,723 people with chronic bronchitis or COPD): people on them were more likely to stay flare-up free, and about 8 needed treating for some nine months to keep one more person free of flare-ups. The review rated this moderate certainty and noted that recent trials showed less benefit (Poole 2019). The newest pooling of oral NAC alone, in 2,609 people with COPD, found a 13% lower risk of flare-ups, with no gain in breathing tests or quality of life (Cai 2026); an earlier one limited to trials since 2000 found no clear difference (Huang 2023). NAC is an add-on to inhalers, never a swap. The bronchitis guide has the trial detail; see also COPD and chronic bronchitis.

Does NAC help OCD, skin picking or hair pulling?

Grade B, mixed, for OCD as an add-on; grade C in adults for hair pulling and skin picking. Pooling 6 trials in 195 adults with moderate to severe OCD, NAC added to an SSRI lowered scores more than placebo between weeks 5 and 8, a result on the edge of statistical significance, but not before week 5 or after week 12 (Eghdami 2024). In 50 adults with trichotillomania (hair pulling), 12 weeks of 1,200 to 2,400 mg daily left 56% of the NAC group much or very much improved by the end, while 16% improved that much on placebo, with gains first seen after 9 weeks (Grant 2009). In 66 adults who picked their skin, 1,200 to 3,000 mg daily over 12 weeks gave 47% much improved against 19% among those who finished (Grant 2016). In 39 children and teens who pulled hair, NAC did no better than placebo (Bloch 2013); anyone under 18 should ask a clinician first. Our trichotillomania page shows D for NAC; that letter grades an anxiety score from the children's trial, not hair pulling itself, and our OCD page doesn't grade NAC yet. More in the OCD guide.

Does NAC help depression, schizophrenia or cravings?

Grade B, mixed, for depression and schizophrenia; grade B for no clear benefit in cannabis use disorder; always on top of usual treatment. For depression, pooling 12 trials (904 people) found a small drop in scores, most clearly in bipolar disorder (Peng 2024), while an earlier pooling of 7 double-blind trials found no change in depressive symptoms and more stomach and gut side effects (Kishi 2020). For schizophrenia, reviews disagree: one saw benefit only after 24 weeks or more (Yolland 2020), another pooling 8 trials (594 people) saw none (Zhang 2024); see does NAC help schizophrenia? For cannabis use disorder, a Cochrane review of 2 trials (270 people) found NAC did not raise quit rates, moderate certainty (Spiga 2025); see do supplements help cannabis withdrawal? Our condition pages don't yet grade NAC for these overall results; where they show a D, it is for other measures such as anxiety or processing speed. Don't stop, skip or swap a psychiatric medicine; see bipolar disorder and schizophrenia.

Does NAC help fertility or PCOS?

Grade C: no clear rise in pregnancies. A review pooling 15 trials (2,330 women) found no clear gain in pregnancy or ovulation, and three of the trials it pooled have since been retracted (Devi 2020). The fertility guide and PCOS guide cover this; once pregnant, follow your midwife or obstetric team.

Does NAC help your liver or fatty liver?

Grade C: no clear effect on fatty liver. In 60 adults with MASLD (fat in the liver linked to weight and blood sugar, once called NAFLD), 2,400 mg a day plus lifestyle advice for 12 weeks did no better than lifestyle advice alone on liver fat, scarring scores or insulin resistance (Ramadan 2026). In 69 adults, 600 mg three times a day for 8 weeks left liver fat, liver enzymes and blood fats unchanged against placebo, though fasting sugar, insulin and CRP fell (Sinaeinejad 2025). See fatty liver and supplements and your liver.

For acetaminophen poisoning, the prescription solution is labeled as an antidote taken by mouth under medical care (NAC label), and hospitals also give it into a vein (Sandilands 2009). They also try it by drip for some other kinds of sudden liver failure, where pooling 4 trials found no clear survival benefit (Orban 2024). Neither use tells you anything about a daily capsule for a healthy liver.

Does NAC raise glutathione?

Grade C: NAC alone did not raise glutathione in COPD trials, and it is only a blood measure. In 24 older adults, glycine plus NAC for 16 weeks corrected low glutathione and improved other lab markers against a placebo (Kumar 2023); that trial combined two supplements, so it can't show what NAC alone does. In COPD trials, oral NAC on its own did not change glutathione levels against placebo (Huang 2023; Cai 2026). A higher blood level is not proof of better health. See glutathione and glycine.

Does NAC help colds, flu, hangovers or blood pressure?

  • Flu-like illness: grade C. In 262 people at 20 Italian centers, most aged 65 or over, 600 mg twice a day for 6 winter months meant fewer and milder flu-like episodes than placebo; infection rates were similar, but only 25% of infected people on NAC got symptoms against 79% on placebo (De Flora 1997). It is one trial.
  • Hangover: grade C, no clear effect. In 49 volunteers, total hangover scores did not differ from placebo; only a subgroup of women did better (Coppersmith 2021). In 40 students, symptoms did not change (Podobnik 2024).
  • Blood pressure: grade C, no clear effect. In 20 people with kidney disease already on blood pressure medicines, taking 1,200 mg daily for 8 weeks did not change blood pressure (Renke 2010).

Does NAC protect your kidneys?

Grade C: no benefit, and no sign of harm, in hospital. In 4,993 people at high risk of kidney damage before an X-ray dye test (angiography), 5 days of oral NAC did not lower death, dialysis or lasting kidney decline at 90 days (4.6% against 4.5%), nor dye-related kidney injury (Weisbord 2018). With kidney disease, ask your kidney team before any supplement.

What we'd skip

  • NAC instead of an inhaler, an SSRI or therapy: the benefits above come from trials where it was added to usual care (Poole 2019; Eghdami 2024).
  • NAC for lung scarring (idiopathic pulmonary fibrosis): in 264 adults over 60 weeks, oral NAC did not slow the loss of lung capacity against placebo (Martinez 2014).
  • NAC to "break down biofilms": grade D, because the work is in lab studies, such as NAC against bacteria growing on urinary catheters (Manoharan 2025).
  • NAC as a "liver cleanse" or before drinking: fatty liver and hangover trials found no clear benefit (Sinaeinejad 2025; Podobnik 2024).

Safety and interactions

  • Nitroglycerin and other nitrates: among 200 people with unstable angina, 35% of those given oral NAC plus a nitroglycerin patch had side effects, mostly intolerable headache, nearly double the rate with the patch alone (Ardissino 1997). In 46 people given both into a vein, 7 on NAC had symptomatic low blood pressure against none without it (Horowitz 1988). Ask your prescriber first.
  • Activated charcoal: the NAC label says charcoal binds NAC in the lab "and may do so in patients and thereby may reduce its effectiveness" (NAC label). Don't take them together; ask a pharmacist.
  • Asthma: the inhaled (nebulized) prescription form can tighten airways, and the label says to watch people with asthma closely (NAC label). Given into a vein for poisoning, NAC can cause rash, itching, swelling and airway spasm, more often in people with asthma or allergies (Sandilands 2009). With asthma, ask before trying capsules.
  • Stomach and gut: in depression trials, stomach and gut side effects were 1.79 times as common as on placebo, about 1 extra person for every 7 treated (Kishi 2020). A review sponsored by a NAC maker (its conflict-of-interest statement says so) found oral doses as high as 3,000 mg daily no worse for the gut than control groups in lung trials (Calverley 2021). The label also notes a slight unpleasant smell at first.
  • Blood thinners and clotting tests: at the high doses hospitals use for acetaminophen poisoning, NAC raised the INR (a clotting test) by 15% to 30% by lowering clotting factors (Nazar 2025). A 6 g oral dose did not undo clopidogrel's effect on platelets in 11 heart patients (Campbell 2005). No studies have tested NAC capsules with apixaban (Eliquis), warfarin or other anticoagulants; ask your prescriber or pharmacist and see supplements and blood thinners.
  • Acetaminophen (Tylenol): taking NAC does not make extra acetaminophen safe; stay within the dose on the label.
  • Diabetes medicines: NAC lowered fasting sugar and insulin in one MASLD trial (Sinaeinejad 2025); check your sugar more often if you add it.
  • Cancer: in mice, NAC sped up lung tumors and raised melanoma spread (Sayin 2014; Le Gal 2015), grade D. If you have cancer, ask your oncology team before taking it.
  • Upper limit: no official upper limit has been set. Lung trials in adults used 600 to 3,000 mg a day (Calverley 2021) and lasted up to 3 years (Poole 2019). Check your stack if you take other products.
  • Pregnancy and breastfeeding: take NAC only if your midwife or obstetric team advises it. For children, ask your child's doctor.
  • Legal status: NAC was approved as a drug in 1963, so the FDA says it falls outside the legal definition of a dietary supplement; since August 2022 the agency has said it will not act against otherwise lawful NAC supplements (FDA guidance).

When to see a doctor

  • Call 911 or Poison Control (1-800-222-1222) after any possible acetaminophen overdose, even without symptoms.
  • Emergency care for wheezing, throat or face swelling, or a widespread rash after a dose.
  • Same day for chest pain, fainting or a pounding headache on nitrates; breathlessness much worse than usual, or blue lips, with COPD.
  • Right away for thoughts of self-harm: call or text 988 in the US.
  • Before starting: see your doctor if you have asthma, kidney disease or cancer, or take nitrates, diabetes medicines or a blood thinner.

Don't stop a prescribed medicine on your own; ask the prescriber or pharmacist. Pregnant or breastfeeding? Your midwife or obstetric team should advise you. Under 18? Talk to a clinician.

FAQ

What is NAC good for? Its best support is for adults with chronic bronchitis or COPD: taken daily for months, it modestly cut flare-ups (grade B). As an add-on to an SSRI, OCD results are mixed (grade B, mixed), and single trials in adults found less hair pulling and skin picking (grade C).

How long does NAC take to work? In lung trials, the flare-up benefit was measured over about nine months on average. In adult OCD trials, scores dropped only at 5 to 8 weeks; in the adult hair-pulling trial, gains first showed after 9 weeks; in schizophrenia, some reviews saw benefit only after 24 weeks.

Does NAC help your liver? For fatty liver, two small trials in adults found no change in liver fat, and the one that measured liver enzymes found no change in them either (grade C). Its liver use is as a hospital antidote for acetaminophen overdose, which is an emergency.

Does NAC thin your blood? At the high hospital doses used for acetaminophen poisoning, it raised the INR by 15% to 30%. No studies have tested NAC capsules with apixaban or warfarin, so ask your prescriber or pharmacist.

Is NAC safe to take long term? Adult lung trials gave it for up to 3 years. A maker-sponsored review of lung trials found gut side effects no more common than in control groups, but depression trials found them more common than on placebo. No upper limit has been set. Avoid it with nitroglycerin unless your prescriber agrees.

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