Also known as NAC, N-Acetyl-L-Cysteine
Acetylated form of the amino acid cysteine and the rate-limiting precursor for glutathione, the body's principal antioxidant; used clinically as the antidote for paracetamol overdose and studied for respiratory and mental health.
Reported side effects:Tolerability / adverse eventsNausea and gastrointestinal upset: the most frequently reported adverse events with oral NAC in trials were gastrointestinal (SR of 5 RCTs); nausea and vomiting are the most common reactions with licensed acetylcysteine (IV, SmPC)
Be careful if: certain health conditions, pregnant
Ask first if you take: other medicines, blood thinners (anticoagulants or antiplatelets)
Suspect a side effect? Report it to the MHRA Yellow Card scheme ↗
We link to relevant studies and leave interpretation to you and your healthcare professional.
The large figures are what the studies reported for each thing they measured. Open a card for every result.
Colour keyReported a benefitNo clear benefitUnclearPossible harmAmber is for highlights, such as where the most research is. It never means a result was good.
No figure given: Obsession and compulsion sub-scores (no clear benefit); Obsession symptoms (reported a benefit).
Also measured alongside: Anxiety symptoms (reported a benefit).
Every resultWhat sources report about side effects, who should be careful, and medicines to ask about first.
| Reported effect | How often | Basis | Sources |
|---|---|---|---|
| Tolerability / adverse events | unknown | Listed by PubMed corpus rows (PubMed 29908912) | Couto JP, Moreira R. Oral N-acetylcysteine in the treatment of obsessive-compulsive disorder: A systematic review of the clinical evidence. Prog Neuropsychopharmacol Biol Psychiatry 2018;86:245-254 (PMID 29908912) |
| Nausea and gastrointestinal upset: the most frequently reported adverse events with oral NAC in trials were gastrointestinal (SR of 5 RCTs); nausea and vomiting are the most common reactions with licensed acetylcysteine (IV, SmPC) | unknown | Listed by UK SmPC (emc / MHRA) (PubMed 29908912) | Parvolex (Acetylcysteine) 200 mg/ml Concentrate for Solution for Infusion — Summary of Product Characteristics, emc, last updated 09-Jan-2024 (Phoenix Labs)Couto JP, Moreira R. Oral N-acetylcysteine in the treatment of obsessive-compulsive disorder: A systematic review of the clinical evidence. Prog Neuropsychopharmacol Biol Psychiatry 2018;86:245-254 (PMID 29908912) |
| Reported effect | How often | Basis | Sources |
|---|---|---|---|
| Anaphylactoid hypersensitivity reactions with licensed IV acetylcysteine (nausea, vomiting, flushing, rash most common; angioedema, bronchospasm, respiratory distress, tachycardia, hypotension more serious; very rarely fatal) — IV-medicine context, dose/route differ from oral supplements | unknown | Listed by UK SmPC (emc / MHRA) | Parvolex (Acetylcysteine) 200 mg/ml Concentrate for Solution for Infusion — Summary of Product Characteristics, emc, last updated 09-Jan-2024 (Phoenix Labs) |
| Applies to | What sources say | Sources |
|---|---|---|
| certain health conditions | The SmPC notes some evidence that patients with a history of atopy and asthma may be at increased risk of anaphylactoid reaction to acetylcysteine; people with asthma or significant allergies should ask a clinician before high-dose use. | Parvolex (Acetylcysteine) 200 mg/ml Concentrate for Solution for Infusion — Summary of Product Characteristics, emc, last updated 09-Jan-2024 (Phoenix Labs) |
| pregnant | Acetylcysteine safety in pregnancy has not been investigated in formal prospective clinical trials (SmPC, licensed IV use); supplement use in pregnancy or breastfeeding warrants clinician advice. | Parvolex (Acetylcysteine) 200 mg/ml Concentrate for Solution for Infusion — Summary of Product Characteristics, emc, last updated 09-Jan-2024 (Phoenix Labs) |
| Severity | Medicine | Sources |
|---|---|---|
| caution | other medicines — NAC potentiates nitrate effects: co-administration with isosorbide dinitrate in chronic heart failure (RCT) enhanced nitrate vasodilation — headaches and hypotension are the practical concern with nitroglycerin-family medicines. [Class 'nitrates' does not exist in the fixed medicine-class list — flagged on JOE-4160.] | Mehra A, et al. Potentiation of isosorbide dinitrate effects with N-acetylcysteine in patients with chronic heart failure. Circulation 1994;89(6):2595-2600 (PMID 8205670) |
| caution | blood thinners (anticoagulants or antiplatelets) — NAC inhibits platelet aggregation (demonstrated ex vivo; obese insulin-resistant subjects showed resistance to this antiaggregating effect), so a theoretical additive antithrombotic effect with anticoagulants/antiplatelets cannot be excluded. | Anfossi G, et al. Platelet resistance to the antiaggregating effect of N-acetyl-L-cysteine in obese, insulin-resistant subjects. Thromb Res 2003;110(1):39-46 (PMID 12877907) |
Parvolex (Acetylcysteine) 200 mg/ml Concentrate for Solution for Infusion — Summary of Product Characteristics, emc, last updated 09-Jan-2024 (Phoenix Labs)Couto JP, Moreira R. Oral N-acetylcysteine in the treatment of obsessive-compulsive disorder: A systematic review of the clinical evidence. Prog Neuropsychopharmacol Biol Psychiatry 2018;86:245-254 (PMID 29908912)Mehra A, et al. Potentiation of isosorbide dinitrate effects with N-acetylcysteine in patients with chronic heart failure. Circulation 1994;89(6):2595-2600 (PMID 8205670)Anfossi G, et al. Platelet resistance to the antiaggregating effect of N-acetyl-L-cysteine in obese, insulin-resistant subjects. Thromb Res 2003;110(1):39-46 (PMID 12877907)
Audited published research for NAC (N-Acetyl Cysteine) by condition. Drill into a pair page for the full breakdown.
What this means: Bars count reported findings, not treatment effectiveness or certainty.
One study may report several findings or appear in more than one pairing. Counts do not show the size of an effect. Comparable numerical estimates are not established for this summary.
| Compound and condition | Findings (count) | Studies (count) | Reported results (finding counts) | How sure? |
|---|---|---|---|---|
| OCD | 9 | 4 | Benefit: 4; no benefit: 4; harm: 1; unclear: 0; not recorded / unrecognised: 0 | Not formally graded |
Where people report using it and what trials suggest
Common claims the trials do not support
N-acetyl cysteine; decades of hospital use for paracetamol overdose, with growing but unproven psychiatric applications.
Evidence grades reflect study quality and consistency, not marketing claims.
Ordered by strength of evidence, then result direction.
01Comparison of adjuvant and neoadjuvant therapies for muscle invasive bladder cancer: A network meta-analysisPetrelli F, et al. · Urologic oncology · 2026PMID 40935764 ↗02The safety and efficacy of N-acetylcysteine as an augmentation in the treatment of obsessive-compulsive disorder in adults: a systematic review and meta-analysis of randomized clinical trialsEghdami S, et al. · Frontiers in psychiatry · 2024PMID 39376972 ↗03The impact of N-acetylcysteine on lactate, biomarkers of oxidative stress, immune response, and muscle damage: A systematic review and meta-analysisSadowski M, et al. · Journal of cellular and molecular medicine · 2024PMID 39632267 ↗04Brazilian Research Consortium on Obsessive-Compulsive Spectrum Disorders guidelines for the treatment of adult obsessive-compulsive disorder. Part I: pharmacological treatmentde Oliveira MVS, et al. · Revista brasileira de psiquiatria (Sao Paulo, Brazil : 1999) · 2023PMID 36749887 ↗05Effect of neoadjuvant chemotherapy on tumor immune infiltration in breast cancer patients: Systematic review and meta-analysisLlano-León M, et al. · PloS one · 2023PMID 37104271 ↗06Clinical Recommendations for Augmentation Agents in Obsessive-Compulsive Disorder Partially Responsive to Serotonin Reuptake InhibitorsGautam M · Journal of clinical psychopharmacology · 2023PMID 37335203 ↗Reported results grouped by condition. Values and units are preserved as recorded; missing information is not estimated.
How to read this table
Reported direction, numerical results and study design are separate. Certainty has not been formally graded in this table.
| What was measured | Reported findings | Result and units | Reported sample and duration | Study / source |
|---|---|---|---|---|
| Adverse events | N-acetylcysteine (NAC) augmentation with SSRIs did not significantly improve Adverse events compared with placebo; the difference versus placebo was not statistically established in 195.No clear benefit | Not reported Recorded unit: Not reported | Sample (as reported): 195 Follow-up: Not reported | Systematic review · 2024 Study detailsThe safety and efficacy of N-acetylcysteine as an augmentation in the treatment of obsessive-compulsive disorder in adults: a systematic review and meta-analysis of randomized clinical trials. Systematic Review |
| Obsession and compulsion Y-BOCS scores | N-acetylcysteine (NAC) augmentation with SSRIs did not significantly improve Obsession and compulsion Y-BOCS scores compared with placebo; the difference versus placebo was not statistically established in 195.No clear benefit | Not reported Recorded unit: Not reported | Sample (as reported): 195 Follow-up: Not reported | Systematic review · 2024 Study detailsThe safety and efficacy of N-acetylcysteine as an augmentation in the treatment of obsessive-compulsive disorder in adults: a systematic review and meta-analysis of randomized clinical trials. Systematic Review |
| Total Y-BOCS score | N-acetylcysteine (NAC) augmentation with SSRIs improved Total Y-BOCS score (p-Value = 0.05) compared with placebo in 195 (five to eight weeks).Benefit seen | p-Value = 0.05 Recorded unit: Not reported | Sample (as reported): 195 Follow-up: five to eight weeks | Systematic review · 2024 Study detailsThe safety and efficacy of N-acetylcysteine as an augmentation in the treatment of obsessive-compulsive disorder in adults: a systematic review and meta-analysis of randomized clinical trials. Systematic Review |
| Yale-Brown Obsessive-Compulsive Scale (OCD symptoms) | N-acetyl cysteine (NAC) did not significantly improve Yale-Brown Obsessive-Compulsive Scale (OCD symptoms) (mean difference at week 20 = 0.53; 95% compatibility interval = -2.18, 3.23; p = 0.70) compared with placebo; the difference versus placebo was not statistically established in 98 (20-week). (p = 0.70)No clear benefit | mean difference at week 20 = 0.53 Recorded unit: Not reported | Sample (as reported): 98 Follow-up: 20-week | Randomised trial · 2022 Study detailsN-acetyl cysteine (NAC) augmentation in the treatment of obsessive-compulsive disorder: A phase III, 20-week, double-blind, randomized, placebo-controlled trial. Randomized Controlled Trial |
| abdominal pain | N-acetylcysteine (NAC) showed harm (adverse effect) on abdominal pain (9 [60.0]; 2 [13.3]; P < .01) compared with placebo in Forty subjects (16-week). (P < .01)Possible harm | 9 [60.0] Recorded unit: Not reported | Sample (as reported): Forty subjects Follow-up: 16-week | Randomised trial · 2017 Study detailsRandomized, Double-Blind, Placebo-Controlled Trial of N-Acetylcysteine Augmentation for Treatment-Resistant Obsessive-Compulsive Disorder. Randomized Controlled Trial |
| anxiety symptoms | N-acetylcysteine (NAC) improved anxiety symptoms (P = .02) compared with placebo in Forty subjects (16-week). (P = .02)Benefit seen | Not reported Recorded unit: Not reported | Sample (as reported): Forty subjects Follow-up: 16-week | Randomised trial · 2017 Study detailsRandomized, Double-Blind, Placebo-Controlled Trial of N-Acetylcysteine Augmentation for Treatment-Resistant Obsessive-Compulsive Disorder. Randomized Controlled Trial |
| Y-BOCS scores | N-acetylcysteine (NAC) did not significantly improve Y-BOCS scores (4.3 points; 25.6 to 21.3; 3.0 points; 24.8 to 21.8; P = .92) compared with placebo; the difference versus placebo was not statistically established in Forty subjects (16-week). (P = .92)No clear benefit | 4.3 points Recorded unit: Not reported | Sample (as reported): Forty subjects Follow-up: 16-week | Randomised trial · 2017 Study detailsRandomized, Double-Blind, Placebo-Controlled Trial of N-Acetylcysteine Augmentation for Treatment-Resistant Obsessive-Compulsive Disorder. Randomized Controlled Trial |
| Y-BOCS obsession subscale | N-acetylcysteine (NAC) augmentation with fluvoxamine improved Y-BOCS obsession subscale (F = 5·44; d.f. = 1·54; P = 0·011) compared with placebo in 44 (10-week). (P = 0·011)Benefit seen | F = 5·44 Recorded unit: Not reported | Sample (as reported): 44 Follow-up: 10-week | Randomised trial · 2016 Study detailsN-acetylcysteine augmentation therapy for moderate-to-severe obsessive-compulsive disorder: randomized, double-blind, placebo-controlled trial. Randomized Controlled Trial |
| Y-BOCS total score | N-acetylcysteine (NAC) augmentation with fluvoxamine improved Y-BOCS total score (F = 5·14; d.f. = 1·64; P = 0·012) compared with placebo in 44 (10-week). (P = 0·012)Benefit seen | F = 5·14 Recorded unit: Not reported | Sample (as reported): 44 Follow-up: 10-week | Randomised trial · 2016 Study detailsN-acetylcysteine augmentation therapy for moderate-to-severe obsessive-compulsive disorder: randomized, double-blind, placebo-controlled trial. Randomized Controlled Trial |
Associated conditions and community-reported outcomes, wrapped together on one page. Aggregates appear only once enough reports arrive.
How this compound is sold in the UK, and where our readers typically find it.
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