Lilly’s Tirzepatide Cuts Weight of Enrollees by 26% in Phase III Trials

Pictured: Eli Lilly sign on building/iStock, jetcityimage

Pictured: Eli Lilly sign on building/iStock, jetcityimage

Promising results from two late-stage trials for Eli Lilly’s experimental weight loss drug tirzepatide, announced by the company Thursday, support its ongoing, fast-tracked review by the FDA.

Tirzepatide, sold under the brand name Mounjaro as a treatment for Type 2 diabetes, was fast-tracked for review by the FDA for the treatment of adults with obesity or overweight with weight-related comorbidities.

Lilly is studying tirzepatide as a treatment for obesity and overweight in the absence of Type 2 diabetes, both with and without exercise. The two latest Phase III studies were intended to uncover the drug's effectiveness alongside exercise, as well as the effects on weight of going off the drug. SURMOUNT-3 and SURMOUNT-4 met all primary and key secondary objectives for tirzepatide compared to placebo, according to the company.

The SURMOUNT-3 trial looked at the safety and efficacy of the drug in a 72-week treatment plan after a 12-week lifestyle intervention. Patients taking tirzepatide lost an average of an extra 21.1% body weight while on the drug, versus placebo patients who, on average, regained 3.3% of their previous weight. Combined with an average 6.9% weight loss in the 12-weeks leading up to the drug application, patients on average lost 26.6% body weight.

The SURMOUNT-4 trial, on the other hand, evaluated the safety and effectiveness of a 52-week dosing regimen after a 36-week open-label lead-in period. By the end of that 36-week period, patients had lost an average of 21.1% body weight. Patients who stayed on tirzepatide lost an average of an additional 6.7% of body weight, while patients given a placebo instead regained 14.8% body weight. On average, patients who stayed on tirzepatide over the whole 88-2eek period lost 26% body weight.

The drug is a GIP and GLP-1 receptor agonist, targeting receptors found in parts of the human brain associated with appetite regulation. Tirzepatide “has been shown to decrease food intake and modulate fat utilization,” Lilly said in a statement.

“The findings from SURMOUNT-3 challenge the notion that patients living with obesity or overweight can achieve their weight loss goals with diet and exercise alone,” Jeff Emmick, Lilly’s senior vice president of product development, said in a statement. “Additionally, the findings from SURMOUNT-4 reinforce that obesity should be regarded like other chronic diseases where chronic therapy may be needed to maintain treatment benefits."

Lilly noted in its release that the “overall safety profile of tirzepatide in both studies was similar to previously reported SURMOUNT and SURPASS trials and to that of incretin-based therapies approved for the treatment of obesity and overweight.” The company also said that most adverse events in the trials were gastrointestinal, and mild-to-moderate in severity.

However, GLP-1 receptor agonists have come under scrutiny in the EU and UK recently, with both the European Medicines Agency (EMA) and the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) investigating reports of suicidal ideation and self-harm risk. The EMA noted in its announcement that suicidal behavior is not listed as a side effect in any GLP-1 receptor agonist approved in the EU.

Connor Lynch is a freelance writer based in Ottawa, Canada. Reach him at

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