Side Effects of MSM (Methylsulfonylmethane)

MSM is considered one of the safest supplements for joints, but even it has side effects. The editorial team gathered data from toxicological and clinical studies to explain which reactions occur, what they depend on, and when a doctor's consultation is needed.

General safety profile of MSM

MSM is among the supplements with one of the most favorable safety profiles among popular "joint" ingredients. The review by Butawan and co-authors (2017), which summarized preclinical and clinical data, concluded that at doses of up to a few grams per day, serious side effects in humans have not been described.

Toxicological studies on rats confirm low toxicity. Horváth and co-authors (2002) found no significant toxic effects with long-term daily administration of very high doses, and Magnuson and co-authors (2007) recorded no teratogenic effect in a fetal development study in rats.

However, "low toxicity" does not mean "complete absence of adverse reactions." In clinical studies and in practice, undesirable effects occur, mostly mild and reversible. It is worth knowing about them in advance in order to respond correctly.

It is also important to distinguish the side effects of MSM itself from problems associated with the quality of the product or other ingredients of the complex. Many supplements contain MSM together with glucosamine, chondroitin, herbs, or sweeteners, which have their own tolerability profile.

The most common side effects

Gastrointestinal complaints are the most common group. People report bloating, rumbling in the abdomen, nausea, loose stools, or, less often, constipation. These symptoms more often appear at the start of intake and with a single large dose on an empty stomach.

Headache and a feeling of fatigue are mentioned in some studies and user reviews. A cause-and-effect relationship here is difficult to establish, since such symptoms also occur in placebo groups.

Sleep disturbances are described mainly in informal reports rather than in controlled studies. Some users notice that an evening dose interferes with falling asleep, so they move the supplement to the morning; this is a simple way to check whether there is a connection.

Skin reactions (itching, rash) are rare. They may be associated with either MSM or excipients. If signs of allergy appear, intake should be stopped.

What the risk of adverse reactions depends on

Dose is the main factor. Clinical studies used from 1.5 to 6 g of MSM per day, and at higher doses gastrointestinal complaints occur more often. A gradual increase in dose over one or two weeks allows the digestive system to adapt.

The regimen also matters. A single large portion on an empty stomach more often causes discomfort than the same daily amount split into two intakes with meals. MSM powder has a slightly bitter taste, and dissolving it in a small amount of liquid can provoke nausea.

Individual sensitivity of the digestive tract matters. People with irritable bowel syndrome or other functional digestive disorders may react to MSM more strongly than others.

Finally, product quality. Raw material obtained with insufficient purification may theoretically contain traces of solvents or heavy metals. Products with certificates from independent laboratories reduce this risk.

Interactions and special situations

There are almost no systematic studies of MSM's interaction with medications. Theoretical concerns relate primarily to anticoagulants and antiplatelet agents: there are isolated reports and assumptions about a possible effect on blood clotting, although there is no convincing clinical data.

People who take warfarin, other anticoagulants, or regular aspirin should discuss taking MSM with a doctor and not combine it with other supplements that may affect clotting (high doses of omega-3, ginkgo, etc.) without medical supervision.

During pregnancy and breastfeeding, there is no data on the safety of MSM in humans. Animal studies are encouraging, but they are insufficient for recommendations, so it is better to refrain from the supplement during this period.

MSM is often confused with DMSO, dimethyl sulfoxide, which is used topically as a solvent and in some medicines. DMSO has a different side-effect profile, including a characteristic garlic odor. These substances are not interchangeable.

• Anticoagulants and antiplatelet agents: consult a doctor.
• Pregnancy and lactation: avoid due to lack of data.
• Chronic liver and kidney diseases: only after discussion with a doctor.

When to see a doctor

Mild digestive symptoms usually do not require medical help and resolve after adjusting the regimen. However, there are situations where continuing self-observation is wrong.

You should immediately seek help at signs of an allergic reaction: a widespread rash, swelling of the face or lips, difficulty breathing. Such reactions to MSM are rare but potentially dangerous regardless of the cause.

A doctor's consultation is also needed for severe or prolonged abdominal pain, blood in the stool, unusual bruising or bleeding, especially if you take medications that affect blood clotting.

Finally, if the joint pain for which you started taking MSM worsens or changes in character, this is a reason for examination rather than for increasing the dose of the supplement.

Editorial conclusions

MSM is generally well tolerated: the most common side effects are mild gastrointestinal complaints, less often headache, sleep disturbances, or skin reactions.

The risk of adverse reactions is reduced by a gradual increase in dose, taking with food, splitting the daily amount, and choosing a quality product.

There is insufficient data on drug interactions and safety for pregnant women, so in these situations the decision should be made by a doctor.

Read more about contraindications, correct intake, and choosing the form of MSM in the articles "Who Should Not Take MSM," "How to Take MSM," and "MSM: Forms and Which to Choose."

References

1. Butawan M, Benjamin RL, Bloomer RJ. Methylsulfonylmethane: applications and safety of a novel dietary supplement. Nutrients. 2017;9(3):290.
2. Horváth K, Noker PE, Somfai-Relle S, et al. Toxicity of methylsulfonylmethane in rats. Food Chem Toxicol. 2002;40(10):1459–1462.
3. Magnuson BA, Appleton J, Ryan B, Matulka RA. Oral developmental toxicity study of methylsulfonylmethane in rats. Food Chem Toxicol. 2007;45(6):977–984.
4. Kim LS, Axelrod LJ, Howard P, et al. Efficacy of methylsulfonylmethane (MSM) in osteoarthritis pain of the knee: a pilot clinical trial. Osteoarthritis Cartilage. 2006;14(3):286–294.
5. 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.
6. Withee ED, Tippens KM, Dehen R, et al. Effects of methylsulfonylmethane (MSM) on exercise-induced oxidative stress, muscle damage, and pain following a half-marathon: a double-blind, randomized, placebo-controlled trial. J Int Soc Sports Nutr. 2017;14:24.