Glutathione Side Effects: Trial Counts and Who Should Ask

In the trials, oral glutathione caused few side effects. In a four-week placebo-controlled trial, five of 40 adults taking 1,000 mg a day reported more wind and loose stools, two flushing and one weight gain, with no change in liver, kidney or blood-count tests;¹ the six-month trial's published report gives no adverse-event data;² and a 2026 review describes stomach discomfort as the most reported effect and serious toxicity as rare.³ Glutathione has no authorised health claim in the UK; what follows is what the trials measured.⁴ This page sits under what does glutathione do in the body.

What side effects did the glutathione trials report?

An open-label series of six children recorded stomach upset in four.⁹ Anything beyond a mild stomach reaction or flushing is a reason to stop and ask a pharmacist. Buyers also mention a sulphurous smell to the powder and a foul taste in liquids; neither is a side effect.

No allergic reaction was reported in these trials, but one is possible with any supplement. The NHS says to call 999 if "your lips, mouth, throat or tongue suddenly become swollen" or "you're breathing very fast or struggling to breathe".¹⁰

Who should ask a pharmacist or GP before taking glutathione?

• Pregnancy and breastfeeding. No trial of glutathione supplements in pregnancy was found, and EFSA's 2026 safety opinion on S-acetyl glutathione, a related form, excludes pregnant and breastfeeding women.¹¹ Ask a midwife or GP.
• Children and under-18s. The same opinion excludes under-10s and sets lower adolescent intakes for that form (190 mg a day at 10 to 13, 269 mg at 14 to 17, 307 mg for adults).¹¹ The one placebo-controlled children's trial was in cystic fibrosis under medical supervision.⁸ Ask a pharmacist, GP or health visitor.
• Asthma or sulphite sensitivity. In eight people with mild asthma, inhaled (nebulised) glutathione cut FEV1 by 19% and caused cough in four and breathlessness in three; the authors attributed it to sulphite forming from glutathione.¹² A capsule is a different product and no study links oral glutathione to asthma, but sulphites are one of the 14 regulated allergens on the Food Standards Agency's list,¹³ so ask first.
• Liver or kidney disease. No oral trial supports use in either (next section). Ask your specialist.
• Anyone on prescribed medicines. No interaction was reported in any trial read, and glutathione is not a substitute for the treatment of any condition the trials studied.

Is glutathione hard on the liver or kidneys?

Not in the trials of healthy adults: the four-week trial found liver and kidney function tests unchanged.¹ The one liver signal is the two women in the 12-week skin trial whose liver enzymes rose and who stopped; the values returned to normal within weeks, and the authors advised blood tests even for over-the-counter supplements.⁵ In liver disease, a 2026 retrospective analysis of 466 people taking 500 mg a day found no overall improvement and no dose-response, and warned against "indiscriminate antioxidant use".¹⁴ No oral trial read shows a kidney signal, and none measured creatinine. None of this is a liver or kidney benefit.

What should you not mix with glutathione?

Nothing specific, on the published record. No trial reported an interaction, and the 2026 review notes that glutathione and its precursors were taken alongside standard antidiabetic and antiretroviral treatment without reported problems.³

• Paracetamol. The hospital antidote to paracetamol overdose is acetylcysteine, a medicine given under a regimen set by clinicians, not a glutathione capsule.¹⁵ If you think you have taken too much paracetamol, call 111 or go to A&E.
• Alcohol. No human trial of glutathione and alcohol was found, so nothing can be said either way.
• Vitamin D, vitamin C, B vitamins, iron, coffee. No study was found reporting a problem or a benefit from any of these pairings.

Is it safe to take glutathione every day, and for how long?

A four-week trial of 1,000 mg a day in 40 adults found no change in red-cell glutathione or two urinary oxidative-stress markers, and a six-month trial of 250 and 1,000 mg a day in 54 adults found glutathione in red cells, plasma and lymphocytes 30 to 35% higher at the top dose and 17 to 29% higher in blood and red cells at 250 mg, with levels returning to baseline a month after stopping.^{1, 2} Nothing longer has been studied; after stopping, stores returned to baseline within a month, with no rebound reported. EFSA's 2026 opinion judged 300 mg a day of the acetylated form safe for adults, noting that trials of ordinary oral glutathione "support the safety of the NF in adults"; it is not a limit for reduced glutathione.¹¹ Timing and forms are at how to take glutathione, and the liposomal pilot at does liposomal glutathione work.

Does glutathione lower your zinc or your B12?

No published study says so. The claim that long-term glutathione depletes zinc circulates online without a citation; literature searches for glutathione supplementation and zinc or copper status found only zinc-supplementation and animal papers, and the six-month trial measured glutathione, not minerals.² The same is true of B12.

Are injections and drips a different question?

Yes, in both safety and law. No glutathione medicine holds a UK marketing authorisation, so any injection or drip is an unlicensed medicine; the MHRA says unlicensed medicines "may not have been assessed by the MHRA" and may be supplied only when a patient's needs are "clinical in nature",¹⁶ and its 2016 position, carried on the Joint Council for Cosmetic Practitioners' page, is that "Cosmetic use is therefore not an admissible special need."¹⁷ The harms on record belong to the needle, not the capsule: a 2025 review lists anaphylaxis and liver toxicity among the serious safety concerns with intravenous glutathione.¹⁸ Reactions can be reported through the MHRA Yellow Card scheme. More at are glutathione injections and drips safe in the UK; skin lightening, safety and legal side only, is at does glutathione lighten skin.

Frequently asked questions

Can glutathione cause diarrhoea or stomach pain?

Loose stools and wind, yes, in a few people: five of 40 in the four-week trial.¹ The 2026 review calls stomach discomfort the most reported effect,³ and four of six children in one case series had stomach upset.⁹ If it persists, stop and ask a pharmacist.

Is glutathione linked to Alzheimer's disease?

No trial has studied glutathione supplements and Alzheimer's disease in either direction. Lower blood glutathione in older adults is a population finding, not a diagnosis, and memory concerns belong with a GP.

Can glutathione increase creatinine?

Not in anything published. The four-week trial found kidney function tests unchanged,¹ and creatinine was not a measured outcome in the others.

Can I drink coffee while taking glutathione?

No study has looked at coffee and glutathione supplements: nothing reported to avoid, nothing reported to gain.

How much glutathione per day is safe?

The trial doses are the facts available: 100 mg a day for four weeks, 250 mg for 12 weeks, 500 mg for four weeks, and 1,000 mg for four weeks and for six months, with the adverse events in the table above.^{1, 2, 5, 6, 7} No UK body has set a limit for reduced glutathione; EFSA's 307 mg a day applies to the acetylated form.¹¹ These are trial doses, not a recommendation.

Sources

1. Allen J, Bradley RD. Effects of oral glutathione supplementation on systemic oxidative stress biomarkers in human volunteers. Journal of Alternative and Complementary Medicine, 2011. PubMed 21875351.
2. Richie JP, et al. Randomized controlled trial of oral glutathione supplementation on body stores of glutathione. European Journal of Nutrition, 2015. PubMed 24791752.
3. Au S, et al. Efficacy and safety of glutathione supplementation in type 2 diabetes and diabetes complications. Nutrients, 2026. PubMed 42451135.
4. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register, updated 19 May 2026. gov.uk.
5. Weschawalit S, et al. Glutathione and its antiaging and antimelanogenic effects. Clinical, Cosmetic and Investigational Dermatology, 2017. PubMed 28490897.
6. Jung ES, et al. Formulation-dependent differences in systemic glutathione availability: comparative pharmacokinetics of orally dissolving film and tablet formulations in healthy adults. European Journal of Pharmaceutics and Biopharmaceutics, 2026. PubMed 42392376.
7. Mawu FO, et al. Effectiveness of oral glutathione in reducing nitric oxide and IL-1α concentrations for clinical improvement in mild to moderate acne vulgaris: a randomized controlled trial. Acta Dermatovenerologica Alpina, Pannonica et Adriatica, 2025. PubMed 41014073.
8. Bozic M, et al. Oral glutathione and growth in cystic fibrosis: a multicenter, randomized, placebo-controlled, double-blind trial. Journal of Pediatric Gastroenterology and Nutrition, 2020. PubMed 32960827.
9. Radwan K, et al. An open-label case series of glutathione use for symptomatic management in children with autism spectrum disorder. Medical Sciences, 2023. PubMed 37987328.
10. NHS. Anaphylaxis. nhs.uk.
11. EFSA Panel on Nutrition, Novel Foods and Food Allergens. Safety of S-acetyl glutathione as a novel food pursuant to Regulation (EU) 2015/2283. EFSA Journal, 2026. PubMed 42683004.
12. Marrades RM, et al. Nebulized glutathione induces bronchoconstriction in patients with mild asthma. American Journal of Respiratory and Critical Care Medicine, 1997. PubMed 9279219.
13. Food Standards Agency. Food allergy and intolerance: advice for consumers, updated 7 August 2026. gov.uk.
14. Philips CA, et al. A cluster analysis of 466 patients demonstrates that glutathione supplementation could preferentially benefit advanced unstable cirrhosis phenotype rather than stable cirrhosis. Frontiers in Pharmacology, 2026. PubMed 42453576.
15. Chiew AL, et al. Interventions for paracetamol (acetaminophen) overdose. Cochrane Database of Systematic Reviews, 2018. PubMed 29473717.
16. MHRA. Supply unlicensed medicinal products (specials), updated 29 January 2025. gov.uk.
17. Joint Council for Cosmetic Practitioners. Glutathione and unlicensed medicines used in cosmetic procedures, carrying the MHRA 2016 wording. jccp.org.uk.
18. Alzahrani TF, et al. Exploring the safety and efficacy of glutathione supplementation for skin lightening: a narrative review. Cureus, 2025. PubMed 40013212.

This article is general information, not medical advice.