MSM (methylsulfonylmethane) for joint complaints in dogs and horses

What is MSM?

MSM (methylsulfonylmethane) is an organic sulphur compound that occurs naturally in plants, animals and humans. Sulphur is a building block of glycosaminoglycans — the molecules that give joint cartilage structure and resilience. This makes MSM biologically plausible as support for joint complaints, although biological plausibility is not proof of efficacy.

MSM is widely sold as part of combination supplements (typically together with glucosamine and/or chondroitin) for dogs and horses. The marketing suggests pain relief, anti-inflammatory effects and restoration of joint function.

What does the research say?

In dogs

Specific canine evidence is completely lacking. There is no published RCT in dogs that has investigated the efficacy of MSM for osteoarthritis or joint pain. Veterinary surgeons who prescribe MSM base this on human literature and clinical impression — a practice that is common in the world of veterinary supplements, but which is not scientifically validated [1][3].

In horses

A crossover study from 2025 (n=10) investigated the effect of MSM supplementation on muscle gene expression after exercise in adult horses [2]. The study showed an altered pattern of inflammation-related genes in skeletal muscle tissue — an indication of involvement in recovery processes. This is not proof of direct joint action or pain relief, and the small sample size severely limits generalisability.

Human research as a starting point

A systematic review from 2008 analysed studies on DMSO and MSM in humans with knee osteoarthritis [1]. MSM showed statistically significant pain reduction, but the effects were clinically modest and the methodological quality of the included studies was moderate. Whether these findings are translatable to dogs or horses has not been investigated.

The University of California (UC Davis) concludes in a narrative review on joint supplements that the evidence for MSM in horses remains limited and that caution is required when extrapolating [3].

Safety profile

The safety profile of MSM is excellent in all species studied. No serious adverse effects have been reported in the available literature. MSM is therefore considered safe if used correctly — but 'safe' does not mean the same as 'effective'.

Points of attention

• MSM is almost always offered in combination products; it is unclear which component causes any potential effects.
• Product quality and dosages vary greatly between manufacturers; there are no standardised veterinary preparations.
• Always have a veterinary surgeon determine the dosage; there are no established veterinary dosing guidelines.

Consideration

MSM can be considered as an addition to veterinary treatment, but it does not replace a diagnosis or proven therapy. If there is doubt about the cause of joint complaints — especially in the case of acute or rapidly worsening symptoms — a veterinary surgeon is the first step.