The blockbuster drug semaglutide, sold as Ozempic for diabetes and as Wegovy for weight loss, now has a new proven benefit: It markedly soothed knee pain in people who are obese and have moderate to severe osteoarthritis, according to a large study.

The effect was so pronounced that some arthritis experts not involved with the clinical trial were taken aback.

“The magnitude of the improvement is of a scope we haven’t seen before with a drug,” said Dr. Bob Carter, deputy director of the National Institute of Arthritis and Musculoskeletal and Skin Diseases. “They had an almost 50 percent reduction in their knee pain. That’s huge.”

Dr. David T. Felson, an arthritis expert and professor of medicine at Boston University School of Medicine, said the study “changes the landscape,” adding that the pain reduction is greater than anything that can be achieved short of knee replacement surgery.

The results were published Wednesday in the New England Journal of Medicine.

Knee osteoarthritis affects nearly one in five Americans over the age of 45. Those with obesity are especially likely to develop it because their weight puts more stress on the knee and because obesity is associated with inflammation, which contributes to deterioration of cartilage.

There are no good medical treatments. Doctors can suggest patients take over-the-counter pain relievers like acetaminophen or ibuprofen. But long-term use of those medications can damage vital organs.