Glutathione side effects: oral, inhaled and injectable forms
Glutathione is promoted for recovery, detox and skin tone, but its safety depends heavily on how it is taken. Our editorial team reviewed the evidence on side effects of oral, inhaled and injectable forms.
Glutathione: the body's own antioxidant
Glutathione is a tripeptide made from three amino acids: glutamate, cysteine and glycine. It is produced in virtually every cell and is often described as the body's master antioxidant. It neutralises reactive oxygen species, regenerates vitamins C and E, and plays a central role in liver detoxification, binding to drugs and toxins so they can be excreted.
Because levels fall with ageing, illness and oxidative stress, glutathione supplements are marketed for immunity, recovery, "detox" and – especially in some markets – skin lightening. Products include oral capsules, liposomal forms, sublingual tablets, nasal sprays and, controversially, injections.
Oral glutathione was long thought to be broken down in the gut. Witschi and colleagues in 1992 found that a single oral dose did not raise blood glutathione. Later, a six-month trial by Richie and co-workers in 2015 reported that daily oral glutathione increased body stores, while Allen and Bradley in 2011 found no significant change in oxidative stress markers after four weeks. The picture remains mixed.
For athletes, the theoretical appeal is reduced oxidative stress and faster recovery. However, the evidence for performance benefits is limited, and the potential downsides deserve equal attention.
Side effects of oral supplements
Oral glutathione is generally well tolerated in trials, with side effects resembling those of other amino-acid-based supplements. Most reports involve the digestive system.
- Bloating, abdominal cramps or wind
- Loose stools
- Unpleasant sulphur-like taste or odour
- Rare allergic reactions such as rash
- Possible reduction in zinc levels with long-term use (suggested, not confirmed)
Long-term safety beyond about six months has not been well studied. As with all antioxidants, there is a theoretical concern that high, chronic doses could blunt beneficial adaptations to training that depend on oxidative signalling, although this has not been demonstrated specifically for glutathione.
Inhaled glutathione and asthma
Nebulised glutathione has been used in some settings for lung conditions, but it carries a specific risk. Marrades and colleagues showed in 1997 that inhaled glutathione caused bronchoconstriction in people with mild asthma, likely because sulphite is released when the molecule breaks down.
People with asthma or sulphite sensitivity should therefore avoid inhaled forms. Breathlessness, wheezing or chest tightness after using any glutathione product require immediate medical attention.
Injectable glutathione: the greatest concern
Intravenous glutathione is promoted by some clinics and online sellers, particularly for skin lightening and "wellness drips". This is where the most serious safety concerns lie.
| Risk | Explanation |
|---|---|
| Infection | Non-sterile products or poor technique can cause local or bloodstream infection |
| Severe allergic reactions | Anaphylaxis is possible with any injected substance |
| Contaminated products | Unregulated products may contain impurities or incorrect amounts |
| Skin and systemic effects | Rashes, and rare reports of serious skin reactions |
| Kidney and liver concerns | Reported in case series of high-dose IV use; not well characterised |
Sonthalia and colleagues reviewed the use of glutathione as a skin-whitening agent in 2016 and concluded that evidence of benefit is weak and that intravenous use carries potential harms without adequate safety data. Regulators in several countries, including the US Food and Drug Administration, have issued warnings about injectable products of uncertain origin.
In the UK, intravenous treatments are subject to medicines and healthcare regulation, and the sale of unlicensed injectable products for cosmetic purposes is a recognised concern. For athletes, intravenous infusions above a defined volume are prohibited under section M2 of the WADA list unless received during hospital treatment or with a Therapeutic Use Exemption, regardless of what is infused.
Interactions and groups to consider
There are few well-documented interactions for oral glutathione, but theoretical concerns exist. Because it influences detoxification pathways, it could alter the metabolism of some medications. People undergoing chemotherapy should not use antioxidant supplements without consulting their oncology team, because antioxidants may theoretically interfere with treatments that work by causing oxidative damage to cancer cells.
Safety data in pregnancy and breastfeeding are insufficient, so supplements are best avoided at these times unless prescribed. People with asthma should avoid inhaled forms, as noted above.
A more practical approach to supporting glutathione levels is through diet. Sulphur-rich foods such as eggs, onions, garlic and cruciferous vegetables provide cysteine and other precursors, while adequate protein intake supplies the necessary amino acids. Regular moderate exercise itself boosts antioxidant defences.
Editorial team's conclusions
Oral glutathione supplements are generally well tolerated, with mild digestive effects being the most common, although the benefits for athletes remain unproven.
Inhaled glutathione can trigger bronchospasm in people with asthma, while injectable products carry the most serious risks, including infection and severe allergic reactions.
Diet, adequate protein and regular training remain the most reliable ways to support the body's own antioxidant systems.
For related reading, see our articles on N-acetylcysteine, on antioxidants and training adaptation, and on IV drips and anti-doping rules.
References
- Witschi A, Reddy S, Stofer B, Lauterburg BH. The systemic availability of oral glutathione. Eur J Clin Pharmacol. 1992;43(6):667–669.
- Richie JP Jr, Nichenametla S, Neidig W, et al. Randomized controlled trial of oral glutathione supplementation on body stores of glutathione. Eur J Nutr. 2015;54(2):251–263.
- Allen J, Bradley RD. Effects of oral glutathione supplementation on systemic oxidative stress biomarkers in human volunteers. J Altern Complement Med. 2011;17(9):827–833.
- Marrades RM, Roca J, Barberà JA, et al. Nebulized glutathione induces bronchoconstriction in patients with mild asthma. Am J Respir Crit Care Med. 1997;156(2):425–430.
- Sonthalia S, Daulatabad D, Sarkar R. Glutathione as a skin whitening agent: facts, myths, evidence and controversies. Indian J Dermatol Venereol Leprol. 2016;82(3):262–272.
