Shares of Eli Lilly & Company advanced on Thursday following the release of groundbreaking data for its experimental obesity treatment, Retatrutide. In a pivotal Phase 3 study, participants achieved an average weight reduction of 28.7% of their body mass, setting a new record for efficacy in late-stage trials of anti-obesity medications.
The results from the TRIUMPH-4 study, published Wednesday, significantly surpassed market expectations. The trial involved 445 adults diagnosed with obesity or overweight who also had knee osteoarthritis. After 68 weeks of treatment with the highest dose of 12 mg, subjects shed an average of 32.3 kilograms.
Notably, 39% of participants achieved a weight loss of 30% or greater, with nearly a quarter losing more than 35%. Concurrently, reported knee pain decreased by 75.8%. Kenneth Custer, a Lilly executive overseeing cardiometabolic health, highlighted the dual impact, stating that the data demonstrates the powerful effect of this triple-agonist for individuals who often contend with pain and limited mobility.
Retatrutide's mechanism of action differentiates it from Lilly's already successful drugs, Mounjaro and Zepbound. While those therapies activate two hormone receptors (GLP-1 and GIP), Retatrutide targets a third pathway by also activating the glucagon receptor. This approach may prove particularly relevant for patients requiring more substantial weight reduction.
The study did report higher rates of adverse events. Among those taking the 12 mg dose, 43% experienced nausea and one-third reported diarrhea. Discontinuation due to side effects occurred in 18.2% of the treatment group, compared to 4% in the placebo group. The company suggested that some participants may have discontinued because the rate of weight loss was perceived as too rapid.
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The development pathway for Retatrutide is extensive. Seven additional Phase 3 trials are scheduled for completion in 2026. These will investigate longer treatment durations of up to 80 weeks and explore the drug's potential in treating conditions like obstructive sleep apnea and chronic lower back pain.
Market analysts view the data as strengthening Lilly's competitive position against rival Novo Nordisk. David Risinger, an analyst at Leerink, described Retatrutid as the drug with the best weight-loss efficacy observed to date. Umer Raffat of Evercore ISI noted that the TRIUMPH-4 trial was not even optimized for maximum weight loss, implying further potential.
In a separate strategic move, Lilly confirmed the completion of its acquisition of Adverum Biotechnologies on December 9. Approximately 64% of Adverum shareholders accepted the offer of $3.56 per share, plus contingent value rights worth up to $8.91 per share. This transaction expands Lilly's gene therapy portfolio, with a focus on addressing age-related ocular diseases.
The pharmaceutical giant, which recently became the first in its industry to reach a $1 trillion market valuation, continues to demonstrate robust growth. Its third-quarter 2025 revenue surged by 54% year-over-year.