Eli Lilly’s Retatrutide Sets New Weight-Loss Records in Phase 3 Trials

Key points

• Retatrutide is a 'triple agonist' targeting GLP-1, GIP, and glucagon, unlike existing drugs that target one or two of these hormones.
• In the TRIUMPH-2 trial for type 2 diabetes, the 12mg dose resulted in an average weight loss of 18.8% (approx. 49.6 lbs), with 31% of participants losing at least 25% of their weight.
• In the TRIUMPH-1 trial for obesity without diabetes, participants lost up to 25% of their weight over 80 weeks, and up to 30% in a subset with severe obesity over 104 weeks.
• The drug significantly reduced HbA1c levels, with 72% of diabetic participants achieving an HbA1c of 6.5% or lower, compared to 29% in the placebo group.
• Side effects were primarily gastrointestinal, including diarrhea (27-34%) and nausea (14-28%), with seven deaths reported in the diabetes trial deemed unrelated to the drug.

Background

Retatrutide represents the next generation of GLP-1-based therapies, following semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro/Zepbound). Previous coverage noted that while these drugs offer benefits beyond weight loss, such as reduced inflammation and cardiovascular improvements, they also carry risks like muscle loss and nutrient deficiencies. The current trials build on this foundation by adding the glucagon receptor to enhance energy expenditure, aiming to surpass the efficacy of bariatric surgery without the surgical risks.

How outlets are covering it

The Guardian and Scientific American emphasized the drug's potential to provide 'other important health benefits' beyond weight loss, such as improved cardiometabolic risk factors and reduced inflammation. NBC News highlighted the magnitude of weight loss, noting it is the most recorded in a diabetes drug trial and rivals gastric bypass surgery. Ars Technica focused on the drug's classification as a 'triple agonist' and the specific reductions in knee pain and sleep apnea events. While all outlets agreed on the efficacy, Scientific American and Ars Technica noted the lack of head-to-head comparisons with existing drugs like tirzepatide as a limitation. NBC News also reported on the emergence of unauthorized 'copycat' versions of the drug being sold through wellness platforms, a point not mentioned in the other sources.

Why it matters

Retatrutide's results suggest a potential shift in the treatment of obesity and type 2 diabetes, offering a non-surgical option with efficacy comparable to bariatric surgery. If approved, it could significantly impact healthcare costs and patient outcomes, though concerns about side effects and the rapid pace of development remain. The drug's success may also accelerate the development of even more potent multi-agonist therapies.

What to watch

Eli Lilly plans to submit retatrutide for regulatory approval 'early next year.' Further trials are needed to compare retatrutide directly with existing drugs like tirzepatide and to assess long-term safety risks, including rare cardiovascular events and pancreatitis. Researchers are also calling for more studies on the drug's effects on pregnancy outcomes in women with type 2 diabetes.