Retatrutide, Eli Lilly's next obesity drug, fueled dramatic weight loss in clinical trial

Retatrutide, Eli Lilly’s next generation of weight loss injections, showed dramatic results in clinical trials, with patients losing an average of up to 71.2 pounds, or 28.7% of their body weight. 

Eli Lilly announced the clinical trial results in a news release Thursday, though they haven’t been peer-reviewed or published in a medical journal. Here’s what to know: 

What is retatrutide? 

Big picture view:

Retatrutide is the next step in the class of drugs known as GLP-1s. Retatrutide is a first-of-its kind triple agonist, meaning it mimics three different hormones that regulate appetite and metabolism.  Zepbound and Mounjaro, Eli Lilly’s other blockbuster weight loss drugs, are dual agonists, while Novo Nordisk’s Wegovy and Ozempic are singular agonists. 

By the numbers:

According to Eli Lilly, the trial included 2,339 patients who were obese or overweight. Participants on the highest dose lost just over 70 pounds on average, or 28.7% of their body weight, after 80 weeks. 

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For patients with a body mass index (BMI) of over 35, the heaviest people in the trial, the weight loss was even higher: They lost an average of 85 pounds, or 30.3% of their body weight, after two years. According to The New York Times, that’s on par with patients who have gastric bypass surgery. 

Clinical trial participants who took Zepbound lost an average of 50 pounds over 72 weeks, while those who took semaglutide, or Wegovy, lost about 33 pounds.

Retatrutide for pain

Lilly also reported that trial participants saw "substantial relief" from osteoarthritis pain, another sign that these blockbuster drugs are treating more than obesity. Zepbound is FDA-approved to treat sleep apnea, while Wegovy is FDA-approved to treat heart disease. These drugs are also being studied to potentially treat alcohol and substance use disorders. 

What they're saying:

"People with obesity and knee osteoarthritis often live with pain and restricted mobility, and may eventually require total joint replacement," Kenneth Custer, executive vice president and president of Lilly Cardiometabolic Health, said in a statement. "We are encouraged by the results … which highlight the powerful effect of retatrutide, a first-in-class triple agonist, on body weight, pain and physical function. We believe retatrutide could become an important option for patients with significant weight loss needs and certain complications, including knee osteoarthritis."

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Retatrutide side effects

Dig deeper:

With more weight loss also came more side effects, like nausea, vomiting, diarrhea and constipation, Lilly reported. The company said 11% of participants on the highest dose left the study because of side effects. That’s a higher dropout rate than previous clinical trials for other obesity drugs. 

When will retatrutide be FDA-approved? 

What's next:

Eli Lilly hasn’t released a date for when it will seek approval by the Food and Drug Administration. The company said it has more retatrutide trials planned this year.