A blockbuster weight loss drug Significantly reduces pain caused by obesity-related knee arthritis and improves a person’s ability to participate in activities such as walking. This is according to a clinical trial carried out in 11 countries, the first of its kind to prove that one of the the new wave of anti-obesity drugs can treat arthritis. The drug, semaglutide, provided pain relief comparable to that of opioid medications.

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By the end of the trial, many participants’ pain had subsided enough that they were no longer eligible for the study, says Henning Bliddal, a rheumatologist at Copenhagen University Hospital in Bispebejerg and Frederiksberg who helped to conduct the test. “They received such effective therapy that they were more or less excluded from the study,” he says.

The findings are “important and could be useful” for people with knee osteoarthritis, says Leigh Callahan, an epidemiologist at the University of North Carolina at Chapel Hill.

The results were published today in the New England Journal of Medicine¹. The trial was sponsored and designed by Novo Nordisk, a company based in Bagsværd, Denmark, which manufactures semaglutide, a drug sold as Ozempic to treat diabetes and Wegovy to treat obesity. Bliddal briefly served as a paid consultant to the company during trial planning.

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Osteoarthritiswhich causes stiff and painful joints, is one of the most common aging-related conditions, and the knee is the most commonly affected joint. Obese people are at higher risk of developing arthritic knees because they put extra pressure on their joints. Obesity also makes symptoms worse, Callahan says. The pain caused by this condition can prevent people from exercising, Bliddal says, making it extremely difficult to lose weight through lifestyle changes alone.

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The trial recruited some 400 participants on five continents and randomly assigned them to receive weekly injections of semaglutide or a placebo. They also received advice on healthy eating and physical activity. At the start of the trial, participants were obese and their average score on a 100-point pain scale was 71 – high enough that walking was painful.

After 68 weeks of injections, participants taking semaglutide had lost significantly more weight than those taking the placebo. They also reported a much greater drop on the pain scale: an average of 42 points, compared to an average of 28 points for the placebo recipients. These participants also noticed greater improvement in their daily functioning, such as climbing stairs.

The improvement probably comes in part from a reduction in the load on the knee resulting from weight loss, the authors write. But semaglutide also has anti-inflammatory effectswhich could help explain the pain relief.

Despite the benefits, Bliddal worries about the long-term outlook for those who use semaglutide to relieve knee arthritis. “Do these guys keep taking semaglutide forever” to manage their pain? People who stop taking the medications usually regain the weight they lostand the drugs are expensive: a monthly supply can cost hundreds of US dollars.

Callahan emphasizes that while the results seem “very exciting,” it’s important that people complement anti-obesity medications with lifestyle changes to maintain their weight long-term.