Eli Lilly’s Retatrutide Shows Promising Weight Loss, But Trial Data Reveals High Dropout Rates

Eli Lilly is advancing its next-generation weight loss drug, retatrutide, with updated timelines for late-stage clinical trial data expected this year. The drug, dubbed the "triple G" due to its mimicry of three hunger-regulating hormones (GLP-1, GIP, and glucagon), has demonstrated significant weight loss potential, exceeding that of existing treatments like tirzepatide.

• Eli Lilly anticipates releasing data from a late-stage retatrutide trial in 2025, earlier than previously projected.
• Retatrutide has shown impressive average weight loss of up to 24.2% in midstage trials.
• A Phase 3 trial, ‘Triumph-4’, revealed high dropout rates, particularly at the highest dosage, with some participants citing perceived excessive weight loss.

Retatrutide operates by mimicking three hormones – GLP-1, GIP, and glucagon – which are crucial in regulating appetite and blood sugar. This triple-action mechanism appears to offer more potent effects on satiety and food satisfaction compared to drugs like tirzepatide (Zepbound/Mounjaro), which targets GLP-1 and GIP, and Wegovy, which targets GLP-1.

In a midstage trial involving adults with obesity or who were overweight, retatrutide helped participants lose an average of 24.2% of their body weight, equating to approximately 58 pounds, after 48 weeks. This is a notable increase compared to tirzepatide’s late-stage trial results, where patients with obesity lost up to 22.5% of their body weight on higher doses.

Eli Lilly has accelerated its timeline, expecting to release data from a 68-week study involving individuals with obesity and knee osteoarthritis later in 2025, a few months ahead of the previously anticipated February 2026 completion date. The company has numerous clinical trials underway for retatrutide, positioning it as a critical component of Lilly’s strategy to maintain its leadership in the weight loss and diabetes market, and to compete effectively with rivals like Novo Nordisk.

However, recent updates from the Phase 3 ‘Triumph-4’ trial have highlighted significant dropout rates. At the highest 12mg dose, 18.2% of participants discontinued the trial, with 12.2% dropping out from the 9mg dose group. This contrasts sharply with the 4% dropout rate in the placebo group. Lilly has indicated that these discontinuations were "highly correlated with baseline BMI and included discontinuations for perceived excessive weight loss."

Despite the dropout concerns, the efficacy of retatrutide remains a significant talking point. Obesity medicine expert Dr. Jennah Siwak described the weight loss results as "insane," comparing them to outcomes seen with bariatric surgery. Dr. Kenneth Custer, Executive Vice President and President of Lilly Cardiometabolic Health, emphasized the potential of retatrutide to offer an important treatment option for patients struggling with significant weight loss needs and related complications, such as knee osteoarthritis.

Eli Lilly is slated to release seven additional Phase 3 readouts for retatrutide in 2026, which will provide further insights into the drug’s safety and efficacy profile. The company faces the challenge of balancing retatrutide’s substantial weight loss benefits against its tolerability, particularly at higher doses, as it progresses through regulatory pathways.

• Eli Lilly to release data on weight loss drug retatrutide in 2025, CNBC.
• Eli Lilly’s New Weight Loss Drug Sees High Dropout Rates, National Today.