Experimental weight loss drug retatrutide significantly reduced chronic knee pain and improved mobility among people with obesity and knee osteoarthritis in two clinical trials led by Northwestern University researchers. The results paired substantial average weight loss with improvements in pain and physical function.

The trials were funded by Eli Lilly and published in The New England Journal of Medicine. Retatrutide, developed by Eli Lilly and Co., is an injectable medication administered once a week and has not yet received FDA approval.

The drug mimics three hormones involved in appetite and metabolism: GLP-1, GIP and glucagon. It has produced substantial weight loss in clinical trials, according to the source.

More than 1,000 adults enrolled in the late stage trials. Participants were overweight or obese, did not have diabetes and experienced painful knee osteoarthritis.

After 68 weeks in one trial and 80 weeks in the other, participants receiving the highest retatrutide dose lost about one quarter of their body weight on average. Researchers then combined findings from the trials for a pooled analysis.

Roughly two thirds of participants treated with retatrutide achieved at least a 50% reduction in knee pain. By comparison, 38% of participants receiving a placebo reached that threshold.

The researchers also reported gains beyond weight loss, pain relief and physical function. Participants experienced lower blood pressure, reduced blood lipid levels and decreased systemic inflammation.

Gastrointestinal problems were the most common side effects recorded during the trials. Serious adverse events occurred more frequently among participants receiving retatrutide than among those given a placebo.

Dr. Thomas J. Schnitzer, a professor at Northwestern University Feinberg School of Medicine and the study’s lead author, described the treatment’s potential for a specific patient group. He cautioned that the findings did not apply to everyone with knee osteoarthritis.

“For people who are obese, not diabetic, have radiographically confirmed knee osteoarthritis that has not progressed to bone on bone, and have consistent moderate knee pain, retatrutide treatment has the potential to result in a significant and meaningful reduction in their knee pain and improvement in their physical function while providing cardiometabolic benefit,” Schnitzer told Fox News Digital.

Researchers expected weight reduction to benefit participants, but one result surprised them. Schnitzer said one of every eight patients taking retatrutide experienced “complete relief of knee pain.”

Painful knee osteoarthritis affects an estimated 15 million Americans. The condition can make routine activities, including standing, walking and climbing stairs, painful challenges.

Conventional treatment options include physical therapy, medications that reduce inflammation and steroid injections. According to the researchers, these approaches frequently provide relief that is limited or temporary.

Earlier research found that losing 5% to 10% of body weight through diet and exercise can ease knee osteoarthritis symptoms. Schnitzer said losing more than 10% through those measures alone can be difficult, particularly when knee pain restricts exercise.

The studies had important boundaries. “People with knee OA who were not overweight or obese were not studied, and individuals who were obese and had more advanced OA were also excluded, so we have no information on them,” Schnitzer said.

Patients who needed knee replacement surgery were also excluded. Researchers therefore do not know whether retatrutide can slow the progression of osteoarthritis or reduce the future need for joint replacement.

Schnitzer said people matching the trial profile who have been unsuccessful at losing weight should speak with their physicians about medication that could support weight loss. Such treatment could also reduce knee pain and provide cardiometabolic benefits, according to Schnitzer.

Medication should not displace healthy daily habits, Schnitzer emphasized. “Before starting pharmacologic treatment for knee pain, people who are overweight should try diet and exercise and consider interventions such as physical therapy,” he advised.

Schnitzer also stressed the continuing value of physical activity during medication treatment. “Also, even for people on weight-loss medications , exercise is an important part of any treatment plan to maintain as much muscle as possible.”