Who Should Not Take MSM (Methylsulfonylmethane)
Methylsulfonylmethane, better known as MSM, is a sulphur compound sold for joint comfort, exercise recovery and even skin and hair. It has a reputation as a very gentle supplement. That reputation is broadly deserved, but the research base is small, and some groups should steer clear or seek advice first. The editorial team explains who they are.
What MSM is and why people take it
MSM is an organic sulphur compound found in small amounts in some fruits, vegetables, grains, milk, coffee and tea. It is closely related to dimethyl sulfoxide (DMSO), a solvent that has been used topically in medicine; part of DMSO is converted into MSM in the body.
Sulphur is a component of amino acids such as methionine and cysteine, of glutathione, and of connective tissue molecules. Manufacturers argue that MSM supplies "bioavailable sulphur" for joints and other tissues, although whether healthy people with adequate protein intake are short of sulphur is debatable.
Research has focused mainly on osteoarthritis of the knee, with small randomised trials suggesting modest improvements in pain and physical function. A smaller number of studies have explored exercise-induced muscle soreness and markers of oxidative stress in athletes, with mixed results.
In the UK, MSM is sold as a food supplement, either on its own or in combination with glucosamine, chondroitin or collagen. Typical products provide 1–3 g per day, and doses up to around 6 g per day have been used in clinical studies.
The safety picture in general
Toxicology studies in animals have shown very low toxicity, and MSM has been granted GRAS (generally recognised as safe) status in the United States for use in foods at specified levels. Human trials lasting up to about three months have reported few side effects.
A review in the journal Nutrients concluded that MSM appears to be well tolerated at doses up to 4 g per day. However, most trials have been small and short, and long-term data are almost absent. "No harm found" in small studies is not the same as "proven safe" for everyone.
When side effects do occur, they are usually mild:
- Bloating, stomach discomfort or diarrhoea
- Nausea, particularly on an empty stomach
- Headache
- Fatigue or, conversely, difficulty sleeping
- Skin rash or itching in occasional cases
Most of these effects ease with a lower starting dose, gradual increase and taking the supplement with meals. If they persist, it is reasonable to stop: MSM's benefits are not strong enough to justify ongoing discomfort.
Groups who should avoid MSM
For some people, the lack of safety data alone is reason enough to avoid MSM. The table below summarises the main groups and the reasoning behind the advice.
| Group | Reason for caution | Editorial recommendation |
|---|---|---|
| Pregnant women | No human safety data | Avoid |
| Breastfeeding women | Unknown transfer to breast milk | Avoid |
| Children and adolescents | Not studied; no established need | Avoid unless advised by a doctor |
| People on anticoagulants or antiplatelets | Theoretical effect on bleeding, limited data | Only after discussion with a pharmacist |
| People with known allergy to sulphur-containing supplements | Possible sensitivity | Avoid or seek advice |
| People with kidney or liver disease | Excretion and metabolism not studied in these groups | Consult specialist first |
| Before surgery | Theoretical bleeding concern | Stop about two weeks beforehand if advised |
It is worth clarifying a common misunderstanding: MSM is not the same as sulphonamide ("sulfa") antibiotics, and an allergy to sulfa drugs does not automatically mean an allergy to MSM. Nor is MSM the same as sulphites, the preservatives that can trigger asthma in sensitive people. Still, anyone with multiple drug or food sensitivities should be cautious with any new supplement.
People with inflammatory bowel disease or irritable bowel syndrome may find that MSM worsens digestive symptoms. A trial at a low dose, with careful observation, is preferable to starting at the full amount on the label.
Possible interactions with medicines and alcohol
There are very few documented drug interactions with MSM, largely because they have not been studied systematically. Because of a theoretical effect on platelet function and limited case reports involving related compounds, pharmacists generally advise caution when MSM is combined with blood-thinning medicines such as warfarin, apixaban, clopidogrel or aspirin.
Anecdotal reports suggest that some people experience stronger effects from alcohol while taking MSM, although this has not been confirmed in controlled studies. Moderating alcohol intake is sensible in any case for people trying to recover from training or improve joint health.
MSM is frequently combined with glucosamine. In that case, the glucosamine component brings its own interaction with warfarin, which is better documented. People on warfarin should therefore be particularly careful with combination joint products.
Topical products containing MSM or DMSO deserve a separate mention. DMSO increases the skin's permeability, potentially carrying other substances into the body. Such products should not be used on broken skin or mixed with other topical medicines without advice.
Using MSM sensibly if it is appropriate for you
If you are a healthy adult and none of the cautions above apply, MSM is a relatively low-risk supplement. Starting with about 1 g per day with food for a week and, if tolerated, increasing to the label dose is a common approach to minimise digestive effects.
Set a defined trial period, for example eight to twelve weeks, with a simple diary of joint pain, stiffness or muscle soreness. Many people notice no difference, and this is consistent with the modest effects seen in research.
For tested athletes, MSM is not on the WADA Prohibited List. Nevertheless, as with any supplement, contamination remains possible, so batch-tested products are preferable.
Finally, persistent joint pain, swelling or night pain should be assessed by a GP or physiotherapist. MSM should never delay diagnosis of conditions such as inflammatory arthritis, stress fractures or significant ligament injuries.
Conclusions of the editorial team
MSM appears well tolerated in short-term studies, with mild digestive complaints as the most common side effect.
Pregnant and breastfeeding women, children, people on anticoagulants, those with kidney or liver disease and anyone preparing for surgery should avoid it or use it only after medical advice.
The evidence for benefit is modest, and long-term safety is largely unknown, so a time-limited trial with honest evaluation is the most reasonable approach for healthy adults.
Related reading from the editorial team: glucosamine and chondroitin side effects, collagen peptides for joints, and evidence on curcumin for exercise recovery.
References
- Butawan M, Benjamin RL, Bloomer RJ. Methylsulfonylmethane: applications and safety of a novel dietary supplement. Nutrients. 2017;9(3):290.
- Kim LS, Axelrod LJ, Howard P, Buratovich N, Waters RF. Efficacy of methylsulfonylmethane (MSM) in osteoarthritis pain of the knee: a pilot clinical trial. Osteoarthritis Cartilage. 2006;14(3):286–294.
- Debbi EM, Agar G, Fichman G, et al. Efficacy of methylsulfonylmethane supplementation on osteoarthritis of the knee: a randomized controlled study. BMC Complement Altern Med. 2011;11:50.
- Brien S, Prescott P, Bashir N, Lewith H, Lewith G. Systematic review of the nutritional supplements dimethyl sulfoxide (DMSO) and methylsulfonylmethane (MSM) in the treatment of osteoarthritis. Osteoarthritis Cartilage. 2008;16(11):1277–1288.
- Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439–455.
