ACR 2026: Retatrutide eases knee OA pain in phase 3 trials

Clinical takeaway: For patients with obesity and painful knee osteoarthritis who have not achieved adequate symptom improvement with lifestyle measures alone, substantial weight loss with retatrutide may offer meaningful reductions in pain and functional limitation. If approved, the therapy could emerge as a disease-management option that addresses both excess weight and osteoarthritis symptoms.

Knee osteoarthritis affects millions of adults and remains a leading cause of pain and mobility loss. Weight reduction is known to improve symptoms, but sustained losses beyond 10% are difficult to achieve with diet and exercise alone, particularly in patients whose pain limits physical activity. New phase 3 findings presented at the American College of Rheumatology annual meeting suggest that substantially greater weight loss with retatrutide may translate into meaningful improvements in pain and function.

In two phase 3 trials enrolling more than 1,000 adults without diabetes who had obesity or overweight and painful knee osteoarthritis, once-weekly retatrutide produced significantly greater pain reduction than placebo. At 68 weeks in TRIUMPH-4, WOMAC pain scores improved by about 3.7 to 4.0 points with retatrutide versus 2.1 points with placebo.

Weight loss was substantial. Participants receiving retatrutide lost an average of 20.0% to 23.7% of body weight over 68 weeks, compared with 4.6% for placebo. A pooled analysis found that roughly two-thirds of retatrutide-treated participants achieved at least a 50% reduction in knee pain, versus 38% of placebo recipients. Participants also showed improvements in blood pressure, lipid levels, and markers of systemic inflammation.

Findings were confirmed in the second trial, TRIUMPH-1-OA. At 80 weeks, WOMAC pain scores improved by 3.2 to 3.6 points across retatrutide dose groups, compared with 1.9 points with placebo. Gastrointestinal adverse events were common, and serious adverse events occurred more often with retatrutide than with placebo.

The phase 3 randomized trials enrolled 445 participants in TRIUMPH-4 and 574 in TRIUMPH-1-OA. Adults without diabetes who had painful knee osteoarthritis and a BMI of at least 27 were assigned to once-weekly retatrutide or placebo, with change in WOMAC pain score serving as the primary outcome in both studies; TRIUMPH-4 also evaluated percentage change in body weight.

Investigators say an important next question is whether retatrutide can slow osteoarthritis progression and reduce the need for total knee replacement. Future research will also explore whether benefits extend to patients with painful knee osteoarthritis who are not overweight or obese.

“The findings are really saying for people who are overweight and have OA, if you lose a significant amount of weight with this treatment, there is a good chance that you’re going to get a meaningful reduction in your knee pain,” said corresponding author Dr. Thomas Schnitzer of Northwestern University. “A major factor is that you’re loading your knees less and therefore, there’s less pain and it allows you to increase your function.”

Source: Schnitzer TJ, et al. (2026 Nov 8) N Engl J Med. Retatrutide Once Weekly in Adults with Knee Osteoarthritis Pain and Obesity