Lilly Halts Muscle-Sparing Obesity Drug Trial, Signaling Shift in FDA Approval Standards

Eli Lilly has terminated a Phase IIb clinical trial for bimagrumab, an experimental muscle-sparing obesity drug, citing "strategic business reasons." This decision comes amid indications of potentially higher approval standards from the U.S. Food and Drug Administration (FDA) for drugs aimed at preserving muscle mass in patients taking weight loss medications.

Bimagrumab Trial Termination and Ongoing Studies

The now-halted study was evaluating bimagrumab alone and in combination with Lilly's blockbuster weight-loss drug tirzepatide (marketed as Zepbound) in 180 patients with type 2 diabetes and overweight or obesity. The trial's primary objective was to assess changes in body weight over 36 weeks, with secondary outcomes focused on body fat and visceral adipose tissue reduction.

A Lilly spokesperson stated that company executives "routinely evaluate our clinical development programs to optimize the potential for each product." Notably, a separate Phase 2 trial involving non-diabetic individuals with obesity is still ongoing. This study is testing various dosing regimens of bimagrumab with or without Zepbound, measuring weight loss and muscle mass preservation, with initial results expected around April 2026.

Shifting Landscape in Muscle-Sparing Obesity Drug Development

The cancellation of Lilly's trial reflects a broader trend in the pharmaceutical industry's approach to developing muscle-sparing obesity drugs. These medications are designed to address a limitation of current weight loss drugs like Zepbound and Novo Nordisk's Wegovy, which can lead to the loss of lean mass alongside fat.

Recent developments suggest that the FDA may be raising the bar for approval of such drugs. Veru, another company in this space, recently announced that the FDA now guides that "incremental weight loss" over a GLP-1 drug alone "is an acceptable primary endpoint to support approval." This indication of higher clearance standards has implications for other companies pursuing muscle-sparing obesity treatments, including Regeneron Pharmaceuticals, Biohaven, and Scholar Rock.

Industry Competition and Recent Developments

Despite the setback with bimagrumab, Lilly remains active in the muscle-preservation space. In June, the company invested up to $650 million in a deal with Juvena Therapeutics to leverage AI for discovering novel drugs that maintain muscle mass and function during weight loss.

Competitors are also making strides in this area:

• Regeneron reported Phase II data for trevogrumab, showing a 51.3% boost in muscle preservation compared to semaglutide monotherapy. When combined with garetosmab, muscle preservation increased to 80.9% relative to semaglutide.
• Scholar Rock announced that apitegromab, used alongside tirzepatide, preserves 55% more muscle mass than tirzepatide alone.

These developments underscore the intense competition and rapid evolution in the field of obesity treatment, as pharmaceutical companies strive to address the complex challenges associated with weight loss and muscle preservation.