NAC Supplement: What It Does, What the Evidence Shows, and How to Use It in Ireland (2026)
NAC (N-acetylcysteine) is one of the most searched supplements in Ireland. This guide covers what it is, what the human research does and doesn't show, how much to take, who should avoid it, and which NAC to buy: 600mg or 1000mg, capsule or tablet.
What it is. NAC (N-acetylcysteine) is a stable form of the amino acid cysteine, which the body uses to make its own glutathione. It is sold in Ireland as a food supplement under FSAI rules, not a medicine, and no EU health claim is authorised for NAC.
What the evidence shows. The strongest human data come from clinical settings: a quantitative review of 9 trials in chronic bronchitis found 48.5% of patients on oral NAC had no exacerbation versus 31.2% on placebo (Stey et al., Eur Respir J, 2000). Evidence for general wellbeing, hangovers or weight in healthy adults is weak or absent.
What to buy. 600 mg capsules are the standard format in Ireland. Probiotic.ie stocks NOW Foods NAC 600mg, NOW Foods NAC 1000mg and Swanson NAC 600mg, all shipped from Dublin with no customs charges.
NAC (N-acetylcysteine) definition: NAC is the acetylated form of the amino acid L-cysteine, made synthetically, used in hospitals as the medicine acetylcysteine and sold in Ireland as a food supplement in 600 mg capsules and 1,000 mg tablets.
- What it is: N-acetylcysteine, a stable form of the amino acid cysteine
- Other names: acetylcysteine (medicine name), N-acetyl-L-cysteine (label name)
- Role in the body: supplies cysteine, the building block the body needs to make glutathione[2]
- Standard supplement serving in Ireland: 600 mg
- Formats at Probiotic.ie: 600 mg capsules, 1,000 mg tablets
- Is it a stimulant? No. It contains no caffeine.
- EU health claim for NAC: none authorised
- Vegan? Depends on the product: NOW Foods NAC 600mg and 1000mg are vegan; Swanson NAC uses a gelatin capsule
- Irish regulatory status: food supplement under FSAI rules, not a medicine
- Irish VAT on supplements: 13.5%
- NAC is not a medicine when sold as a food supplement, and it is not sold to treat, prevent or cure any condition.
- NAC is not the same product as glutathione. It is a precursor the body uses to make glutathione.
- NAC is not proven to prevent hangovers or make drinking alcohol safer.
- NAC is not a weight-loss supplement. There is no good evidence it causes weight loss in healthy adults.
- Hospital uses of acetylcysteine (paracetamol overdose, mucus clearance) are medicine uses and do not transfer to a supplement.
What is well-supported: NAC supplies cysteine for glutathione synthesis (Atkuri et al., Curr Opin Pharmacol, 2007), and oral NAC reduced exacerbations versus placebo in chronic bronchitis trials (Stey et al., Eur Respir J, 2000).
What is not proven: any benefit for general wellbeing, hangovers, weight loss or "detox" in healthy adults.
Human dose range in trials: commonly 600 mg a day, with some supervised trials using up to 2,400 mg a day in divided doses.
Key safety note: check with a GP or pharmacist if you have asthma, take blood thinners or nitrates, or take any prescription medication.
The clinical and mechanistic research discussed in this article relates to NAC (N-acetylcysteine) as a studied compound. It should not be read as a claim that NOW Foods NAC 600mg, or any other product sold by Probiotic.ie, produces these effects. These products are food supplements, not medicines. No authorised EU health claim is made for NAC on this page or on any product.
NOW Foods NAC 600mg, 100 Vegan Capsules
600 mg NAC per capsule in a plant-based capsule, with 25 mcg selenium (45% NRV) and 50 mcg molybdenum. Selenium contributes to the protection of cells from oxidative stress.
Current price on the product page, including Irish VAT at 13.5%. Food supplement, not a medicine. No customs charges. Free DPD delivery on Republic of Ireland orders over €75.
What is NAC?
NAC stands for N-acetylcysteine. It is the amino acid L-cysteine with an acetyl group attached, which makes it more stable.
In hospitals the same compound is the medicine acetylcysteine, used for paracetamol overdose and to thin mucus.[1] As a supplement in Ireland, it is sold as a food, and the medicine uses do not carry over.
| Name on the label | What it means |
|---|---|
| NAC | Common supplement name |
| N-acetyl-L-cysteine | Full label name, same compound |
| Acetylcysteine | Medicine name, same compound |
| L-cysteine | The base amino acid, a different product |
How NAC works: the glutathione connection
Glutathione is made from three amino acids, and cysteine is usually the one in shortest supply. NAC is a stable way to deliver cysteine, which the body then uses to make glutathione.[2]
Supplies cysteine for the body's own glutathione production.
Evidence: established biochemistry [2]Its –SH group can act as an antioxidant directly in laboratory studies.
Evidence: laboratory studies [3]Breaks bonds in mucus proteins. This is the basis of its medicine use.
Evidence: clinical pharmacology [1]Proposed to influence inflammatory signalling pathways.
Evidence: mostly preclinical [3]Mechanism is context, not proof. A pathway seen in a lab does not mean a capsule produces a benefit in people.
NAC benefits: what the evidence actually shows
The quality of NAC evidence varies a lot by area. Most of the stronger trials are in clinical settings, run alongside medical care. That tells you what was studied, not what a supplement will do for a healthy adult.
Chronic bronchitis
Stey et al. pooled 9 trials of oral NAC: 48.5% of patients on NAC had no exacerbation versus 31.2% on placebo (relative benefit 1.56).[4] A later meta-analysis by Cazzola et al. also examined exacerbations.[5] This is a clinical population, not a supplement claim.
Stey C et al. Eur Respir J. 2000;16(2):253-62. PMID 10968500.
PCOS
Thakker et al. pooled randomised trials of NAC in women with PCOS, most run alongside fertility treatment.[6] The trials were small and varied in design. PCOS is a medical condition, and any NAC use belongs in a conversation with your GP.
Thakker D et al. Obstet Gynecol Int. 2015. PMC4306416.
OCD, as an add-on
A double-blind trial added NAC (up to 2,400 mg a day) to standard medication in adults with treatment-resistant OCD and reported a greater reduction on the Y-BOCS scale than placebo.[7] Results have not been consistently repeated, and NAC is not a replacement for OCD treatment.
Afshar H et al. J Clin Psychopharmacol. 2012;32(6). PMID 23131885.
Anxiety and depression
Trials of NAC across mental health conditions have been pooled in meta-analyses,[8] but evidence for anxiety or depression in the general population is preliminary. Professional support comes first.
Zheng W et al. Acta Psychiatr Scand. 2018. PMID 29457216.
Liver
Acetylcysteine is standard hospital care for paracetamol overdose.[1] Studies of NAC supplements for liver markers in other settings are small and results are not consistent.[3] The hospital use does not transfer to a supplement.
Kidney protection in imaging
Early hospital trials of NAC before contrast scans looked positive. Larger trials did not confirm it, and guidelines became more cautious.[9]
Hangovers, weight and "detox"
The reasoning sounds plausible, but there is no good human trial evidence that NAC prevents hangovers, causes weight loss or "detoxes" healthy adults.
NAC dosage: how to take it correctly
600 mg is the standard serving in Ireland. Follow your product label. The table shows doses used in published research, which is not a prescription.
| Context | Dose used | Notes |
|---|---|---|
| Everyday supplement use | 600 mg once daily | Most common Irish format. Follow the label. |
| Chronic bronchitis trials | Commonly 600 mg a day | Clinical trials [4] |
| OCD add-on trial | Up to 2,400 mg a day, divided | Supervised, alongside medication [7] |
When to take NAC
- With food if you get nausea. It can be taken either way.
- Any time of day. No trial shows morning beats evening.
- Split larger amounts into two servings, morning and evening.
- Consistency beats timing. Pick a time you'll stick to.
Which NAC should I buy? 600mg vs 1000mg
Same compound, three formats. The right one depends on how many tablets you want to take, whether you need vegan, and whether you want selenium included. Swipe the table on a phone.
| Product | NAC per unit | Label serving | Pack | Also contains | Vegan |
|---|---|---|---|---|---|
| NOW Foods NAC 600mg | 600 mg capsule | 1 capsule, 1 to 2 times daily | 100 capsules | Selenium 25 mcg (45% NRV), molybdenum 50 mcg | Yes |
| NOW Foods NAC 1000mg | 1,000 mg tablet | 1 tablet, 1 to 3 times daily | 120 tablets | NAC only | Yes |
| Swanson NAC 600mg | 600 mg capsule | 1 capsule daily | 100 capsules | NAC only | No (gelatin) |
- Want the standard 600 mg in a vegan capsule? NOW Foods NAC 600mg. It also includes selenium, and selenium contributes to the protection of cells from oxidative stress.
- Want fewer tablets? NOW Foods NAC 1000mg puts 1,000 mg in one tablet.
- Want NAC on its own, one a day? Swanson NAC 600mg. Note the gelatin capsule.
The selenium statement is an authorised EU health claim for selenium, at 25 mcg (45% NRV) per capsule. It is not a claim for NAC. Prices change, so each product page shows the current price including 13.5% VAT.
Side effects and who should avoid NAC
At typical oral supplement doses NAC is generally well tolerated. Side effects are more common at higher doses or on an empty stomach.[1]
Common side effects
- Digestive: nausea, stomach upset, diarrhoea. Taking it with food helps.
- Smell and taste: a sulphur smell is normal for NAC.
- Headache: reported in some trials, mostly at higher doses.
Rare but serious
- Allergic reactions: documented mainly with intravenous hospital use.[1]
- Bronchospasm: mainly with inhaled acetylcysteine in people with asthma.
- are pregnant or breastfeeding
- have asthma
- take blood thinners, antiplatelet drugs or nitrates (such as nitroglycerin)
- have kidney or liver disease
- take any prescription medication, or have surgery coming up
| Medicine | Possible interaction | What to do |
|---|---|---|
| Nitrates (e.g. nitroglycerin) | May increase low blood pressure and headache[1] | Avoid unless your doctor agrees |
| Blood thinners / antiplatelets | Possible added effect on bleeding | Ask your GP or pharmacist |
| Activated charcoal | May reduce NAC absorption | Separate by at least 2 hours |
Not a complete list. If you take regular medication, ask a pharmacist before starting NAC.
NAC vs glutathione supplement: which is better?
They work differently. NAC is a building block; glutathione supplements supply the finished molecule. For a full guide to glutathione itself, see our glutathione supplement Ireland guide.
| Factor | NAC | Oral glutathione |
|---|---|---|
| How it works | Precursor: body makes its own glutathione from it | Supplies glutathione directly |
| Absorption | Oral NAC is absorbed[2] | How much standard oral glutathione survives digestion is debated |
| Human research | Larger body of trials | Smaller, growing |
| Interchangeable? | No. They are different products with different evidence. | |
Is NAC legal in Ireland? The regulatory context
- Yes, it's legal. NAC is sold in Ireland as a food supplement under FSAI rules.[10] It is not a controlled substance and not a prescription medicine in supplement form.
- No authorised health claim. No EU health claim is authorised for NAC under Regulation (EC) No 1924/2006, so no NAC label can lawfully promise a health benefit.
- FSAI notification is not approval. The FSAI states notification is not an approval or authorisation process.[11] Be wary of "FSAI approved" on any supplement.
- The US FDA debate doesn't apply here. The FDA's questions about NAC as a US dietary supplement concern US law only.[12]
- 13.5% VAT. Food supplements carry Ireland's reduced VAT rate.[13]
Buying NAC in Ireland: what to look for in 2026
- The right name: NAC, N-acetylcysteine or N-acetyl-L-cysteine.
- Amount per capsule or tablet and the label serving per day.
- Full ingredient list, including extras like selenium.
- Capsule type: vegetarian (hypromellose) or gelatin.
- No disease claims. "Cures", "treats" or "detoxes" is a red flag.
- Ships from Ireland? Supplements ordered from outside the EU can attract VAT and customs charges (see customs charges Ireland).
Product details on this page were checked by Probiotic.ie against the live product listings on 14 October 2026: NOW Foods NAC 600mg (600 mg NAC, 25 mcg selenium, 50 mcg molybdenum per vegan capsule; 100 capsules; 1 capsule once or twice daily), NOW Foods NAC 1000mg (1,000 mg per vegan tablet; 120 tablets; 1 tablet one to three times daily) and Swanson NAC 600mg (600 mg per gelatin capsule; 100 capsules; 1 capsule daily). Always check the label on the pack you receive.
The research discussed in this article relates to NAC as a studied compound and should not be read as a claim that any product sold by Probiotic.ie produces these effects. These products are food supplements, not medicines. The only authorised health claim on this page is for selenium, at the stated amount in NOW Foods NAC 600mg.
Ready to order? NOW Foods NAC 600mg
The standard 600 mg serving in a vegan capsule, with selenium. Or choose the 1,000 mg tablet or Swanson NAC-only capsule.
Current price on the product page, including Irish VAT at 13.5%. Food supplement, not a medicine. Compare all NAC supplements.
FAQs: NAC supplement Ireland
What is NAC supplement good for?
NAC (N-acetylcysteine) is most studied as a source of cysteine, the building block the body uses to make glutathione (Atkuri et al., Curr Opin Pharmacol, 2007). Human research also covers chronic bronchitis, PCOS and OCD, but those are clinical settings, not reasons to self-treat. No EU health claim is authorised for NAC, so it is sold in Ireland as a food supplement, not a medicine.
What does NAC supplement do?
NAC supplies cysteine, which the body uses to make glutathione. It also has a free thiol group that can act as an antioxidant in laboratory studies, and in hospital medicine acetylcysteine is used to break down mucus and to treat paracetamol overdose (StatPearls: Acetylcysteine). Hospital uses of acetylcysteine are medicine uses and do not transfer to a food supplement.
Should I take NAC 600mg or 1000mg?
Both contain the same compound. 600 mg capsules are the most common format in Ireland and match the dose used in many published trials. A 1,000 mg tablet gives more NAC per tablet, so fewer tablets for the same daily amount. Choose the format that suits your routine and follow the label: NOW Foods NAC 600mg suggests 1 capsule once or twice daily, NOW Foods NAC 1000mg suggests 1 tablet one to three times daily, and Swanson NAC 600mg suggests 1 capsule daily.
Is NAC supplement legal in Ireland?
Yes. NAC is sold legally in Ireland as a food supplement under EU food law, overseen by the Food Safety Authority of Ireland (FSAI) (FSAI). It is not a controlled substance. No EU health claim is authorised for NAC under Regulation (EC) No 1924/2006. The US FDA debate about NAC as a supplement does not apply in Ireland. Irish VAT on food supplements is 13.5% (Revenue).
What are NAC supplement side effects?
The most commonly reported side effects at oral doses are digestive: nausea, stomach upset and diarrhoea, more often at higher doses or on an empty stomach (StatPearls). A sulphur smell or taste is common. Speak to a GP or pharmacist first if you have asthma, take blood thinners or nitrates, take any prescription medication, or are pregnant or breastfeeding.
What is the best NAC supplement in Ireland?
There is no single best NAC. Check that the label says N-acetylcysteine or N-acetyl-L-cysteine, the amount per capsule or tablet, the full ingredient list, the capsule type (vegetarian or gelatin) and that the product makes no disease claims. Probiotic.ie stocks three: NOW Foods NAC 600mg (vegan capsules with selenium and molybdenum), NOW Foods NAC 1000mg (vegan tablets) and Swanson NAC 600mg (NAC only, gelatin capsules).
How much NAC supplement should I take per day?
Follow the label on your product. 600 mg once daily is the most common consumer serving in Ireland. Clinical trials have used higher amounts, for example up to 2,400 mg a day in divided doses as an add-on to medication in OCD (Afshar et al., J Clin Psychopharmacol, 2012), but those were supervised trials, not a guide to self-dosing. Do not exceed the label dose without advice from a GP or pharmacist.
Should I take NAC or glutathione?
They are different products. NAC is a precursor: the body converts it to cysteine and uses that to make its own glutathione. Oral glutathione supplies glutathione directly, but how much of a standard oral dose survives digestion is debated. NAC has the larger body of published human research as an oral supplement. Our glutathione supplement Ireland guide covers glutathione in detail.
Can I take NAC supplement with alcohol?
The idea comes from the fact that alcohol metabolism uses up glutathione. There is no good human trial evidence that NAC prevents or reduces hangovers. Taking NAC does not make drinking safer. If you are concerned about alcohol and your liver, speak to a GP.
Is NAC supplement good for PCOS?
NAC has been studied in women with PCOS, mostly alongside fertility treatment. A systematic review and meta-analysis by Thakker et al. pooled the randomised trials (Obstet Gynecol Int, 2015). PCOS is a medical condition, NAC is not a treatment for it, and any use should be agreed with your GP or specialist.
Where can I buy NAC supplement in Ireland?
NAC is sold in Irish pharmacies, health food shops and online. Probiotic.ie stocks NOW Foods NAC 600mg, NOW Foods NAC 1000mg and Swanson NAC 600mg, shipped from Dublin with tracked delivery, no customs charges, and free DPD delivery on Republic of Ireland orders over €75 (delivery information). Check the label before you buy, wherever you buy.
- NAC (N-acetylcysteine) is a stable form of the amino acid cysteine that the body uses to make glutathione.
- NAC is not the same as glutathione; it is a precursor.
- No EU health claim is authorised for NAC under Regulation (EC) No 1924/2006.
- A quantitative review of 9 trials found 48.5% of chronic bronchitis patients on oral NAC had no exacerbation versus 31.2% on placebo (Stey et al., Eur Respir J, 2000, PMID 10968500).
- 600 mg is the standard NAC supplement serving in Ireland; supervised trials have used up to 2,400 mg a day.
- There is no good human evidence that NAC prevents hangovers or causes weight loss.
- In Ireland, NAC is sold as a food supplement under FSAI rules, not a medicine; 13.5% VAT applies.
- Probiotic.ie stocks NOW Foods NAC 600mg, NOW Foods NAC 1000mg and Swanson NAC 600mg, shipped from Dublin with no customs charges.
Related guides from Probiotic.ie
This guide was first published on 1 April 2026 and reviewed by Probiotic.ie on 14 October 2026. In the review we:
- Re-checked every journal citation against PubMed or publisher records, and corrected two PMIDs and two mis-attributed references from the original version.
- Reviewed StatPearls (acetylcysteine), Atkuri 2007, Stey 2000, Cazzola 2015, Thakker 2015, Afshar 2012, Zheng 2018 and the KDIGO 2012 guideline.
- Separated hospital medicine uses of acetylcysteine from food supplement use throughout.
- Checked FSAI food supplement rules and confirmed no EU health claim is authorised for NAC.
- Verified the three NAC products against the live Probiotic.ie listings.
- Made no disease-treatment claims and no health claims for NAC.
This guide has not been reviewed by a clinician. It is not medical advice.
Sources
- [1] StatPearls. Acetylcysteine. Treasure Island (FL): StatPearls Publishing; NCBI Bookshelf NBK537183. — ncbi.nlm.nih.gov/books/NBK537183
- [2] Atkuri KR, Mantovani JJ, Herzenberg LA, Herzenberg LA. N-Acetylcysteine: a safe antidote for cysteine/glutathione deficiency. Curr Opin Pharmacol. 2007. PMID 17602868. — pubmed.ncbi.nlm.nih.gov/17602868
- [3] Mokhtari V et al. A review on various uses of N-acetyl cysteine. Cell J. 2017. PMC5241507. — pmc.ncbi.nlm.nih.gov/articles/PMC5241507
- [4] Stey C, Steurer J, Bachmann S, Medici TC, Tramèr MR. The effect of oral N-acetylcysteine in chronic bronchitis: a quantitative systematic review. Eur Respir J. 2000;16(2):253-62. PMID 10968500. — pubmed.ncbi.nlm.nih.gov/10968500
- [5] Cazzola M, Calzetta L, et al. Influence of N-acetylcysteine on chronic bronchitis or COPD exacerbations: a meta-analysis. Eur Respir Rev. 2015;24(137):451. PMID 26324807. — pubmed.ncbi.nlm.nih.gov/26324807
- [6] Thakker D et al. N-Acetylcysteine for polycystic ovary syndrome: a systematic review and meta-analysis of randomized controlled clinical trials. Obstet Gynecol Int. 2015. PMC4306416. — pmc.ncbi.nlm.nih.gov/articles/PMC4306416
- [7] Afshar H et al. N-acetylcysteine add-on treatment in refractory obsessive-compulsive disorder: a randomized, double-blind, placebo-controlled trial. J Clin Psychopharmacol. 2012;32(6). PMID 23131885. — pubmed.ncbi.nlm.nih.gov/23131885
- [8] Zheng W et al. N-acetylcysteine for major mental disorders: a systematic review and meta-analysis of randomized controlled trials. Acta Psychiatr Scand. 2018. PMID 29457216. — pubmed.ncbi.nlm.nih.gov/29457216
- [9] KDIGO Clinical Practice Guideline for Acute Kidney Injury. 2012. — kdigo.org (PDF)
- [10] Food Safety Authority of Ireland. Food Supplements: legislation and guidance. — fsai.ie/legislation/food-legislation/food-supplements
- [11] Food Safety Authority of Ireland. Food Supplements – Legislative Requirements. 2024. — fsai.ie (PDF)
- [12] US Food and Drug Administration. Final guidance on enforcement discretion for certain NAC products (US only). — fda.gov
- [13] Revenue Commissioners. Tax and Duty Manual: VAT treatment of food supplement products. — revenue.ie (PDF)