Is there any evidence that DMSO creams and gels help arthritis pain? I see companies selling these products all over the internet and in health food stores.

In two words, not much. DMSO stands for dimethyl sulfoxide, a compound that’s had a long and somewhat complicated history of being used in topical, oral, and even intravenous form as an alternative therapy for a variety of conditions, from headaches to musculoskeletal problems to burns and wounds to athlete’s foot to the autoimmune disease scleroderma—sort of like a wonder drug.

In the mid-1960s, the FDA banned much research on DMSO because its use in animals, even topically, was said to be linked with the possible development of cataracts. Shortly after, the agency reversed its decision, which had been based on unsubstantiated evidence of harm. But the effect of the restrictions had lingering effects: It led many responsible investigators to discontinue their studies of DMSO and scared patients away from using it. The only FDA-approved use for DMSO today is as a prescription drug given intravenously to treat a bladder condition called interstitial cystitis.

Nowadays, DMSO is mostly sold as an over-the-counter product that’s applied to the skin to purportedly relieve pain from arthritis (osteoarthritis or rheumatoid) or tendinitis, for example. However, according to the Arthritis Foundation, though topical DMSO appears to have some anti-inflammatory activity, the few human studies done on it have produced conflicting results. Most of the studies are old, and some have methodological problems.

Moreover, it’s hard to know if topical DMSO is safe, according to the National Center for Complementary and Integrative Health at the National Institutes of Health. Again, that’s because there have been too few human studies. Side effects including skin irritation and skin rash have been reported. Also, it is absorbed through the skin and can give a garlic smell to the breath, and it can affect some medications people may be taking, including anticoagulant drugs.

Here’s a sampling of some of the more recent research on DMSO:

• DMSO has been found to reduce joint swelling in mice with arthritis, with lab studies suggesting that there may be several mechanisms to account for pain-relieving properties of the compound, including anti-inflammatory and antioxidant activity and the ability to reduce transmission of signals along pain-inducing nerve fibers. Among the anti-inflammatory properties associated with DMSO in the lab is a reduction in the production of pro-inflammatory chemicals called cytokines.
• A human study in the International Journal of Pharmaceutical Sciences and Research in 2019 involved middle-aged and older people with knee osteoarthritis who were randomized into one of two groups. For three months, they were treated three times a day with either a topical nonsteroidal anti-inflammatory (NSAID) prescription drug (diclofenac) plus DMSO, or with the topical NSAID plus linseed oil (the control group). The researchers found greater improvement in joint pain and stiffness in the DMSO-based NSAID group, which might be attributed to DMSO acting to enhance transdermal absorption of the pain medication.
• An older but much larger human study, published in the journal Pain in 2009, compared the topical NSAID diclofenac combined with DMSO to DMSO alone in more than 500 people with knee osteoarthritis (as one arm of the trial). After three months, the NSAID-DMSO group had the most symptom improvement. But the authors concluded that this was not because of any beneficial effect of DMSO itself but rather, as noted above, because DMSO might have improved absorption of the NSAID.

BOTTOM LINE: Because of a paucity of data from human trials showing a benefit of topical DMSO, we don’t recommend using this OTC product for relief of pain or any other symptoms. If you have arthritis or another condition or injury that is causing pain, talk with your doctor about potentially more effective treatments. But if you decide to use DMSO with a topical anti-inflammatory drug (such as diclofenac), check with your doctor or pharmacist about any possible interactions with other drugs you may be taking. The Arthritis Foundation says DMSO should not be used if you have diabetes, asthma, or liver, kidney, or heart conditions.