GLP-1 Medicines and Knee Osteoarthritis: What We Know About Pain and Mobility

Knee osteoarthritis can make everyday things, like stairs, walks and getting up from a chair, feel much harder. Because extra body weight increases the load on the knees, and weight loss has long been known to ease osteoarthritis symptoms, researchers have asked whether GLP-1 medicines can help with knee pain too. The best evidence so far comes from the STEP 9 trial of semaglutide.

What did STEP 9 study?

STEP 9 randomly assigned 407 adults with obesity (BMI 30 or higher) and moderate knee osteoarthritis with at least moderate pain to weekly semaglutide 2.4 mg or placebo for 68 weeks. Everyone also got counseling on physical activity and a reduced-calorie diet. Most participants (about 82%) were women, the average age was 56, and the average BMI was about 40. The study was funded by Novo Nordisk, the manufacturer.

What did it find?

• Weight: about −13.7% with semaglutide versus −3.2% with placebo.
• Knee pain: on the WOMAC pain scale (0–100, higher is worse; average starting score about 71), pain fell by about 42 points with semaglutide versus about 28 with placebo.
• Physical function: scores on a standard physical-function questionnaire improved more with semaglutide (about 12 points versus 6.5).
• Side effects: serious adverse events were similar between groups, but more people stopped semaglutide because of side effects (6.7% vs 3.0%), mostly gastrointestinal ones.

Notice that the placebo group improved a lot, too. That's common in pain trials and shows why a comparison group matters so much: some improvement comes from counseling, attention, natural ups and downs, and expectations, not only the medicine.

What about newer medicines?

In December 2025, Eli Lilly announced topline results from TRIUMPH-4, a phase 3 trial of retatrutide in 445 adults with obesity and knee osteoarthritis, reporting larger reductions in knee pain and weight than placebo over 68 weeks. As of October 2026, those results are company-reported and not yet published in a peer-reviewed journal, and retatrutide is an investigational medicine that is not approved anywhere. Our article on retatrutide's 2026 trial results has more context.

Why it's not just "less weight equals less pain"

Less weight means less mechanical stress on the joint, and researchers are also studying effects on inflammation and physical capacity. STEP 9 can't settle every biological explanation. Knee symptoms are also shaped by injury, joint alignment, muscle strength, sleep, mood and other health conditions, and not every type of arthritis or joint problem was represented in the trial.

What this means for treatment conversations

As of October 2026, no GLP-1 medicine has a US indication specifically for knee osteoarthritis. If knee pain is limiting your life, a clinician can look at the cause and talk through evidence-based options for osteoarthritis and, where appropriate, weight management. Physical therapy, strengthening exercise and pain-management plans still matter, and this article isn't a reason to change them. If you're building strength while losing weight, our guide to strength training on GLP-1 may help.

A practical next step

Ask which options fit your type and severity of arthritis, how much activity is safe for you, and how to measure function (like walking distance or stair comfort) as well as pain. Get prompt medical care if a joint suddenly becomes very swollen, hot and red, especially with a fever, or if you can't bear weight after an injury.

The research is promising because it links a weight-management trial to something people really feel day to day. The takeaway is still specific to the drug and population studied, not a blanket promise for all joint pain.