NOW NAC 600mg – N-Acetyl Cysteine 100 Veg Capsules
NOW NAC 600mg – N-Acetyl Cysteine 100 Veg Capsules
✎ Too long? Here is what matters:
- ✅ NAC is your body's glutathione raw material — published research documents that NAC raises intracellular glutathione levels; glutathione is described in biochemistry literature as the body's master antioxidant
- ✅ One of the most-studied supplement compounds in existence — NAC has been the subject of hundreds of peer-reviewed randomised controlled trials across respiratory health, oxidative stress, liver function research, and more
- ✅ Selenium: EU-authorised health claim — under EU Regulation 1924/2006, selenium is authorised to claim it "contributes to the protection of cells from oxidative stress" and "contributes to the normal function of the immune system"
- ✅ 600 mg NAC per capsule — the dose used in the majority of published human clinical trials on NAC
- ✅ 100 capsules per bottle — one of the best value NAC formulas available in Ireland
- ✅ Vegan ✔ Gluten-free ✔ No soy, milk, egg, fish, or tree nuts ✔
- ✅ Made by NOW Foods — independently tested, GMP-certified since 1968
ⓘ Food supplement. Not a medicine. Full research references below.
📝 In-Depth Guide
NAC Supplement: What It Is, What the Evidence Says, and How to Use It Safely
Our editorial team has published a full evidence-led guide to NAC — covering the science behind glutathione and cysteine pathways, how to interpret "NAC benefits" claims under Irish and EU rules, dosing context, safety checks, and a verification-first buying framework. If you want to understand exactly what you are taking and why, read this before you buy.
📖 Read the Full NAC Guide →Published 23 February 2026 | Probiotic.ie Editorial Team | Evidence-led. Not medical advice.
NOW Foods NAC 600 mg — N-Acetyl Cysteine With Selenium & Molybdenum: What the Research Says
N-Acetyl Cysteine — NAC — is one of the most extensively researched compounds in nutritional science. It has been studied in hundreds of peer-reviewed randomised controlled trials (RCTs), examined across more therapeutic contexts than almost any other supplement ingredient, and used clinically in hospitals worldwide for decades. Its primary role in published research is as a precursor to glutathione — the tripeptide antioxidant that published biochemistry literature describes as the most abundant and important intracellular antioxidant in the human body.
This formula pairs 600 mg of NAC with selenium from L-selenomethionine — the organic, highly bioavailable form of selenium — and molybdenum from sodium molybdate. Selenium carries fully EU-authorised health claims under Regulation 1924/2006. This is not marketing language. These are legally permitted, EFSA-substantiated statements about what selenium contributes to in the body.
This is a food supplement, not a medicine. The research cited below relates to NAC and its constituent compounds as studied in published settings. It does not constitute a claim that this specific product will produce the same outcomes in any individual.
The EFSA-Authorised Claims for Selenium in This Formula
The selenium in this product is provided as L-selenomethionine — the organic form of selenium with the highest documented bioavailability in published research. Under EU Regulation (EC) No 1924/2006, the following health claims are legally authorised for selenium and may be stated on food supplement labels and product pages in Ireland and the EU:
- Selenium contributes to the protection of cells from oxidative stress
- Selenium contributes to the normal function of the immune system
- Selenium contributes to normal thyroid function
- Selenium contributes to the maintenance of normal hair and nails
- Selenium contributes to normal spermatogenesis
Each capsule of this product provides 25 mcg of selenium — 45% of the EU Nutrient Reference Value — from L-selenomethionine, the form used in the human bioavailability studies on which these EFSA claims are based.
What Published Research Has Documented About NAC
📊 NAC as a Glutathione Precursor — The Core Mechanism
Glutathione (GSH) is a tripeptide composed of three amino acids: glutamate, glycine, and cysteine. Of these three, cysteine is the rate-limiting precursor — meaning the body's ability to synthesise glutathione is directly constrained by cysteine availability. NAC is a stable, bioavailable form of cysteine that, once absorbed, is deacetylated to free cysteine inside cells. Multiple published studies have documented that oral NAC supplementation raises both plasma cysteine levels and intracellular glutathione concentrations. Published review literature describes NAC's primary antioxidant role as its ability to increase intracellular glutathione concentration — the most abundant nonprotein thiol in the body and one of the main antioxidants responsible for maintaining cellular redox status.
📊 Oxidative Stress — RCT Evidence
A randomised crossover trial comparing NAC, oral glutathione, and sublingual glutathione in adults found that NAC supplementation was effective for increasing glutathione levels, and that the GSH/GSSG ratio — a key marker of cellular redox status — was significantly higher in the NAC group than in the oral glutathione group. A higher GSH/GSSG ratio indicates lower oxidative stress burden at the cellular level.
📊 The 600 mg Dose — Why It Matters
The dose in this product — 600 mg per capsule — is the dose that appears most consistently across published human clinical trials on NAC. Published pharmacokinetic research has documented that at 600 mg dosing, glutathione concentrations were consistently and significantly elevated post-dose. At the recommended dose of one to two capsules daily, this product delivers 600–1,200 mg of NAC — within the range studied across the broadest body of published RCT evidence.
📊 Respiratory Research — Multiple RCTs and Meta-Analyses
NAC has one of the longest clinical research histories in respiratory medicine of any supplement compound. It has been studied in the context of chronic obstructive pulmonary disease (COPD), acute respiratory conditions, and mucolytic applications. NAC's mucolytic properties — its ability to break disulfide bonds in mucus glycoproteins — are the basis of its licensed pharmaceutical use in hospital settings across Europe, including as an intravenous treatment for paracetamol overdose.
📊 Physical Performance Research — 2023 Systematic Review
A 2023 systematic review published in Nutrients (Fernández-Lázaro et al., PubMed ID: 37299425) evaluated controlled trials on NAC supplementation and physical performance in adult men, concluding that NAC supplementation may regulate glutathione homeostasis, produce antioxidant effects, and improve exercise performance, while noting that further studies are needed to clarify the relevance of its use in this context.
📊 Safety Profile — Decades of Clinical Use
At oral supplement doses (600–1,800 mg/day), NAC has been documented as well tolerated across a large body of published clinical trial data spanning several decades. Published review literature describes NAC's toxicity as uncommon and dependent on route of administration and high dosages. The most commonly reported adverse effects at oral doses are mild gastrointestinal symptoms including nausea and stomach discomfort.
Why This Formula — NAC + Selenium + Molybdenum
Most NAC supplements contain NAC alone. This formula adds two important cofactors:
- Selenium (as L-selenomethionine, 25 mcg — 45% NRV): Selenium is a required cofactor for glutathione peroxidase (GPx) — the enzyme that uses glutathione to neutralise hydrogen peroxide and lipid hydroperoxides inside cells. Without adequate selenium, the glutathione NAC helps produce cannot be fully utilised by the GPx enzyme system. L-selenomethionine is the organic, most bioavailable form, and the form used in the EFSA-assessed bioavailability studies.
- Molybdenum (as sodium molybdate, 50 mcg — 111% NRV): Molybdenum is an essential trace mineral and cofactor for several key enzymes including sulfite oxidase, which is involved in the metabolism of sulfur-containing amino acids — the same biochemical pathway that NAC, as a sulfur-containing compound, participates in.
Product Facts
- N-Acetyl Cysteine (NAC): 600 mg per capsule
- Selenium (from L-Selenomethionine): 25 mcg — 45% NRV
- Molybdenum (from Sodium Molybdate): 50 mcg — 111% NRV
- Capsules per bottle: 100 (50-day supply at 2 caps/day; 100-day at 1 cap/day)
- Capsule type: Hypromellose (plant-derived cellulose) — suitable for vegans and vegetarians
- Free from: Wheat, gluten, soy, milk, egg, fish, shellfish, tree nuts
- Manufactured by: NOW Foods, USA — GMP-certified, independently tested since 1968
- Distributed by: Probiotic.ie, Dublin, Ireland
Full Ingredient List (per capsule)
- N-Acetyl Cysteine — 600 mg
- Selenium (from L-Selenomethionine) — 25 mcg
- Molybdenum (from Sodium Molybdate) — 50 mcg
- Hypromellose (vegan capsule shell)
- Stearic acid (vegetable source)
- Citric acid
Allergen note: Not manufactured with wheat, gluten, soy, milk, egg, fish, shellfish, or tree nut ingredients.
How to Take
Take one capsule one to two times daily with food and water. Do not exceed two capsules in any 24-hour period.
In the majority of published clinical trials on NAC, the dose studied was 600 mg taken two to three times daily. This product delivers 600–1,200 mg per day at the recommended dose — within the range most commonly used in the published human trial literature.
If you are taking any prescription medication — particularly paracetamol, nitroglycerin, or medications affecting blood pressure — consult your doctor or pharmacist before use.
Who Looks at This Product?
People who typically seek NAC + selenium supplements include those who:
- Have researched glutathione and want to raise levels via the most bioavailable oral precursor rather than direct glutathione supplementation
- Are interested in compounds studied extensively in the context of oxidative stress and cellular redox balance
- Want the 600 mg dose that matches the majority of published human clinical trial evidence
- Are looking for a clean-label vegan formula free from the most common allergens
- Trust NOW Foods as a manufacturer with a long track record of third-party testing and GMP production
This product is intended for adults aged 18 and over. It is not a medicine and is not intended to diagnose, treat, cure, or prevent any disease or health condition.
Frequently Asked Questions
What is NAC and what does it do in the body?
N-Acetyl Cysteine (NAC) is a stable, bioavailable form of the amino acid cysteine. Once absorbed, NAC is converted to free cysteine inside cells. Cysteine is the rate-limiting precursor to glutathione — meaning it is the building block the body needs most to synthesise glutathione. Published research documents that oral NAC supplementation raises both plasma cysteine and intracellular glutathione concentrations. Glutathione is described in biochemistry literature as the body's most abundant intracellular antioxidant. For a full explanation of the mechanism, safety, and evidence, read our complete NAC guide.
Why not just take a glutathione supplement directly?
Oral glutathione has poor bioavailability — it is broken down in the digestive tract before it can enter cells intact. Published research comparing oral glutathione and NAC has found that NAC is more effective at raising intracellular glutathione levels, because NAC is absorbed as a precursor and glutathione is synthesised inside the cell where it is needed. This is why NAC is often described in research literature as the preferred oral strategy for raising glutathione.
Why does this formula include selenium?
Selenium is a required cofactor for glutathione peroxidase (GPx) — the enzyme that uses glutathione to neutralise harmful reactive oxygen species inside cells. Without adequate selenium, glutathione cannot be fully deployed by the GPx enzyme system. The L-selenomethionine form used in this product is the organic, most bioavailable form of selenium. Under EU Regulation 1924/2006, selenium is authorised to claim it contributes to the protection of cells from oxidative stress and contributes to the normal function of the immune system.
What is molybdenum doing in this formula?
Molybdenum is an essential trace mineral and cofactor for several key enzymes including sulfite oxidase — which is involved in the metabolism of sulfur-containing amino acids. NAC is itself a sulfur-containing compound, so molybdenum supports the broader sulfur amino acid metabolic pathway that NAC participates in. At 50 mcg per capsule, this product delivers 111% of the EU Nutrient Reference Value for molybdenum.
How many capsules are in the bottle and how long will it last?
Each bottle contains 100 capsules — more than most NAC products on the market. At one capsule per day that is a 100-day supply. At two capsules per day (the maximum recommended dose) it is a 50-day supply. This makes it one of the best value NAC formulas available in Ireland.
Is this suitable for vegans and vegetarians?
Yes. The capsule shell is made from hypromellose — a plant-derived cellulose. The formula contains no gelatin and no animal-derived ingredients. It is free from gluten, soy, milk, egg, fish, shellfish, and tree nuts.
Can I take NAC if I am on medication?
Consult your doctor or pharmacist before taking NAC if you are on prescription medication. This is particularly important if you take paracetamol regularly, nitroglycerin, or medications affecting blood pressure or blood clotting. NAC is known to interact with certain drug pathways and your healthcare provider should be aware of your full supplement intake.
What are the known side effects of NAC?
At oral supplement doses, NAC has a well-established safety profile documented across decades of clinical use and published trials. The most commonly reported side effects at oral doses are mild gastrointestinal symptoms — including nausea, stomach discomfort, and occasionally loose stools — particularly when taken on an empty stomach. Taking capsules with food is recommended. If you experience any adverse reaction, discontinue use and consult a healthcare professional.
Why choose NOW Foods as a brand?
NOW Foods has been manufacturing nutritional supplements since 1968 and is one of the most independently tested supplement brands in the industry. Their manufacturing facilities operate to GMP standards. For consumers who prioritise label accuracy and manufacturing quality, NOW Foods is consistently ranked among the most trusted brands in independent supplement testing.
How quickly will my order arrive in Ireland?
Orders are dispatched from Dublin, Ireland via DPD next-day delivery. Most orders placed before the daily dispatch cut-off arrive the following working day within Ireland.
What is the returns policy?
Probiotic.ie processes returns in line with Irish and EU consumer protection law. If your product arrives damaged or is not as described, contact Probiotic.ie directly and the team will resolve it for you.
Where can I read more about NAC before I buy?
We have published a full evidence-led guide to NAC covering the glutathione mechanism, how to interpret "NAC benefits" claims under Irish and EU food supplement rules, dosing context, a safety checklist, and a verification-first buying framework. Read the complete NAC supplement guide here →
Important Information
This product is a food supplement. It is not a medicine and is not intended to diagnose, treat, cure, or prevent any disease or health condition. Research cited on this page relates to NAC and its constituent compounds as studied in published scientific settings and does not constitute a claim that this specific product will produce the same results in any individual.
Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Do not exceed the stated recommended daily dose. Intended for adults aged 18 years and over.
If you are pregnant, breastfeeding, taking any medication, or under medical supervision, consult your doctor or qualified healthcare professional before use.
Discontinue use and seek medical advice if any adverse reaction occurs. Do not use if the tamper-evident seal under the cap is broken or missing. Store in a cool, dry place, away from direct sunlight. Keep out of reach of children.
Manufactured by: NOW Foods, Bloomingdale, Illinois, USA
Distributed by: Probiotic.ie, Dublin, Ireland