Glutathione is one of your body’s own molecules — produced in every cell and well tolerated in most people at dietary levels. Side effects from glutathione supplementation are uncommon and generally mild. That said, higher doses and specific formulations do carry some considerations worth understanding before you start supplementing.
This article covers what the research says about glutathione side effects, the differences between supplementation routes, and when caution is warranted. For the flipside — the evidence-backed benefits of glutathione — see our guide to glutathione benefits and what the research actually shows.
Is Glutathione Generally Safe?
Yes. Glutathione is a naturally occurring molecule produced by the body and found in food. Its long-term presence in human physiology means it is well tolerated under normal circumstances. Regulatory bodies in the UK and EU consider glutathione safe for use in food supplements at typical doses.
The most commonly studied oral doses in clinical research range from 250mg to 1,000mg per day, with the majority of studies reporting no significant adverse events. A randomised controlled trial published in the European Journal of Nutrition (Richie et al., 2015) found that 250mg or 1,000mg per day of oral glutathione over six months was well tolerated in 54 non-smoking adults, with no clinically significant adverse effects reported.
It’s worth noting that a 2025 systematic review and meta-analysis raised questions about how much standard oral glutathione actually raises blood glutathione levels, highlighting ongoing debate about oral bioavailability. Safety in trials has been consistent, but efficacy remains an area of active research — which is one reason many people opt for NAC (see below) as a precursor approach.
Glutathione Side Effects at a Glance: Oral vs Liposomal vs IV
The three main routes of glutathione supplementation have very different safety and availability profiles. This table summarises the key differences:
| Route | Typical Dose | Common Side Effects | Serious Risks | UK Availability |
|---|---|---|---|---|
| Standard oral | 250–1,000mg/day | Mild GI (bloating, loose stools, nausea) — uncommon | None documented at standard doses | Widely available as food supplement |
| Liposomal oral | 500–1,000mg/day | Similar GI profile to standard oral; generally mild | None identified; 2023 trial showed no changes in liver or kidney markers over 30 days | Available as food supplement |
| Intravenous (IV) | 600–2,000mg+ per session | Injection-site reactions, nausea, metallic taste, dizziness | Endotoxin contamination, sepsis, Stevens-Johnson syndrome, renal/thyroid dysfunction, deranged LFTs, anaphylaxis | Not available as consumer supplement; medical supervision only |
The clear pattern: oral and liposomal glutathione have a very benign safety profile; IV glutathione carries substantially greater risks, most of which relate to administration quality and contamination rather than the molecule itself.
Reported Side Effects of Oral Glutathione Supplementation
Side effects from standard oral glutathione supplements are uncommon. When they do occur, they tend to be mild and gastrointestinal in nature:
- Bloating or abdominal discomfort — occasionally reported, particularly at higher doses; usually resolves with dose reduction or taking the supplement with food
- Loose stools — reported infrequently; may be more likely with higher doses
- Nausea — uncommon; more likely with higher doses or in those with gastrointestinal sensitivity
- Flatulence and flushing — reported in a small number of participants in controlled trials
These are not specific to glutathione — similar effects are seen with many amino acid and peptide supplements at higher doses.
Glutathione and Zinc: What the Evidence Actually Shows
You’ll sometimes see claims that long-term glutathione supplementation depletes zinc. It’s worth being clear about where this evidence stands, because the picture is more nuanced than supplement blogs often suggest.
The mechanistic relationship actually runs in the other direction: zinc deficiency impairs glutathione synthesis, because zinc is required for enzymes involved in GSH metabolism. Animal and cell-culture studies confirm this. What is not well established is the reverse claim — that taking oral glutathione depletes zinc in humans. Direct human clinical trial evidence for this is essentially absent.
In practice: at typical supplemental doses (250–500mg per day) there is no good reason to expect clinically meaningful effects on zinc status. If you’re using higher doses over extended periods, ensuring adequate dietary zinc from meat, shellfish, legumes, and seeds is sensible general nutrition — but you shouldn’t assume you need a separate zinc supplement on the basis of glutathione use alone.
Liposomal Glutathione Side Effects
Liposomal glutathione — encapsulated in fat-based particles to improve absorption — generally has a similar side effect profile to standard oral glutathione. The same gastrointestinal effects are possible.
Recent clinical research supports the safety of liposomal formulations. A 2023 study of 600mg per day of liposomal glutathione over 30 days in healthy adults found no significant changes in liver enzymes (ALT, AST, ALP) or kidney markers (creatinine), and the product was well tolerated throughout. Earlier work by Sinha and colleagues (2018) reached similar conclusions at doses of 500mg and 1,000mg per day over one month.
Because liposomal glutathione may be absorbed more effectively than standard oral glutathione, there is a theoretical consideration that effects may occur at lower doses — but the clinical trial evidence to date has not identified any unique safety concerns with liposomal formulations. For more detail on how liposomal glutathione actually performs, see our liposomal glutathione guide.
Intravenous (IV) Glutathione Side Effects
IV glutathione is used in some clinical and aesthetic settings and carries a substantially different risk profile to oral supplementation. Documented adverse effects include:
- Endotoxin contamination and sepsis — the most concrete documented harm. In 2019 the FDA issued a warning after seven patients experienced adverse events linked to endotoxin-contaminated L-glutathione powder used by compounding pharmacies. Symptoms of endotoxin exposure range from fever and chills to hypotension, shock and death.
- Skin reactions and allergic responses — including rare but serious reports of Stevens-Johnson syndrome and toxic epidermal necrolysis
- Renal dysfunction — reported in case series of high-dose IV use
- Thyroid dysfunction — documented in case reports, particularly with high-dose long-term IV use
- Deranged liver function tests — in one trial of IV glutathione for skin lightening, approximately one third of patients showed abnormal liver function markers
- Anaphylaxis — rare but documented
IV glutathione is not available as a consumer supplement in the UK and should only be administered under medical supervision in a properly regulated clinical environment. The contamination and compounding-quality risks are as significant as any direct pharmacological concern, which is why regulatory agencies have repeatedly flagged unregulated IV clinics as the higher-risk setting.
Skin Whitening and High-Dose Use
Glutathione has become widely used in some markets as a skin-lightening agent, typically at doses much higher than those used in health research (sometimes exceeding 2,000mg per day via IV). Regulatory agencies in several countries — including the Philippines’ FDA and the WHO — have issued warnings about high-dose IV glutathione for skin lightening, citing risks of kidney damage, thyroid dysfunction, nerve damage, and infection from unregulated administration.
These risks are associated with high-dose IV administration in uncontrolled settings, not with oral supplementation at standard doses. The distinction is important: the evidence base and safety profile for oral glutathione supplementation at typical doses is very different from high-dose IV use.
Glutathione Side Effects vs NAC Side Effects
Most people seeking to support their glutathione levels will encounter NAC (N-acetyl cysteine) as an alternative or first-line option — because NAC raises intracellular glutathione more reliably than standard oral glutathione supplements. We cover this comparison in more detail in our NAC vs glutathione guide.
NAC has its own side effect profile, which is also mild at standard doses:
- Nausea and gastrointestinal discomfort — more commonly reported with NAC than with glutathione, particularly at doses above 600mg
- A characteristic sulphurous smell — inherent to the molecule; not a health concern
- Headache — occasionally reported at higher doses
For a full discussion of NAC benefits, dosage and side effects, see our NAC supplement guide, or explore our own NAC+ 600mg vegan supplement.
Who Should Be Cautious With Glutathione Supplementation
Most healthy adults can take oral glutathione supplements without concern. However, specific groups should seek advice before supplementing:
- People undergoing chemotherapy — glutathione plays a role in cellular detoxification, and some oncologists have concerns about antioxidant supplementation interfering with treatment (glutathione may protect cancer cells alongside healthy cells). This requires discussion with your oncologist.
- People with asthma — inhaled forms of glutathione (nebulised) have triggered bronchospasm in some asthmatic individuals; oral supplementation does not carry this risk, but caution and medical guidance are appropriate
- Pregnant and breastfeeding women — insufficient data exists on glutathione supplementation in pregnancy; dietary sources are appropriate but supplementation should be discussed with a midwife or healthcare provider
- People on medications affecting glutathione — paracetamol at high regular doses depletes glutathione; nitroglycerin interacts with glutathione metabolism. Check with a pharmacist or prescriber if you take regular medications.
If you’d rather support your glutathione levels through diet and lifestyle first, see our guide on how to boost glutathione naturally.
Frequently Asked Questions
Does glutathione cause any serious side effects?
At typical oral supplemental doses (250–1,000mg per day), serious side effects are rare. The reported side effects are primarily mild and gastrointestinal — bloating, loose stools, or nausea, particularly at higher doses. Serious adverse effects are associated with high-dose IV use, not oral supplementation.
Can glutathione cause skin problems?
Skin rash has occasionally been reported with IV glutathione use, and rare but serious reactions including Stevens-Johnson syndrome have been documented. Oral supplementation at standard doses has not been associated with skin reactions in clinical research. Some people use glutathione for skin effects — specifically lightening — but at the doses and routes (IV) typically used for this purpose, safety concerns are more significant.
Does glutathione deplete zinc?
The evidence for this claim is weak. Mechanistically, zinc deficiency can impair glutathione synthesis — but the reverse (oral glutathione supplementation depleting zinc in humans) has not been demonstrated in clinical trials. At typical supplemental doses there is no good reason to expect clinically meaningful effects on zinc status.
Is it safe to take glutathione every day?
Based on available research, daily oral glutathione supplementation at standard doses appears safe for at least six months, which is the duration of the longest published controlled trial. Long-term safety data beyond this period is limited, though there is no mechanistic reason to expect problems at typical doses. As with any supplement, periodic reassessment is sensible.
Can I take glutathione with other supplements?
Glutathione is generally compatible with other supplements. It is often taken alongside vitamin C (which supports glutathione recycling), NAC (which supports glutathione synthesis), and selenium (which supports the recycling enzymes). There are no well-established adverse interactions with common supplements at standard doses.
This article is for informational purposes only and does not constitute medical advice. If you have a digestive health condition, are taking medication, or are considering supplementation, speak to your GP or a registered dietitian before making changes.
