Lilly Reports Up to 28.3% Weight Loss with Retatrutide in Phase 3 Obesity Trial

Eli Lilly announced positive topline results from the Phase 3 TRIUMPH-1 study evaluating retatrutide, an investigational triple hormone receptor agonist for adults with obesity or overweight and at least one weight-related comorbidity.¹

According to the company, participants receiving the highest 12 mg dose achieved an average body weight reduction of 28.3% over 80 weeks, equivalent to approximately 70 pounds. More than 45% of participants lost at least 30% of their body weight, a level commonly associated with bariatric surgery outcomes.¹

The once-weekly injectable targets glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon receptors simultaneously, positioning retatrutide within a growing class of multi-receptor metabolic therapies.²

Why are triple agonist therapies drawing industry attention?

Retatrutide has generated significant attention because of the scale of weight reduction observed during clinical development. Earlier Phase 2 findings published in the New England Journal of Medicine demonstrated up to 24.2% average weight loss at 48 weeks among adults with obesity.²

The newly released Phase 3 data extend those findings into a larger late-stage study population involving more than 2,300 participants.¹ Lilly also reported that patients with baseline body mass indexes of 35 or higher who continued into a 104-week extension achieved average weight reductions exceeding 30%.¹

Researchers additionally observed improvements in cardiometabolic markers, including waist circumference, triglycerides, systolic blood pressure, and inflammatory biomarkers.

“Obesity is a chronic disease, and people living with obesity deserve treatment options that match the complex biology of their neurometabolic disease,” said Ania Jastreboff, MD, PhD, lead investigator for the trial.¹

What safety findings emerged from the TRIUMPH-1 study?

Lilly stated that adverse events were generally consistent with incretin-based therapies currently available on the market.¹ The most frequently reported side effects included nausea, diarrhea, constipation, and vomiting, with gastrointestinal events increasing alongside dose escalation.

Discontinuation rates due to adverse events ranged from 4.1% in the 4 mg group to 11.3% in the 12 mg group.¹ Analysts continue monitoring tolerability closely as obesity therapies move into broader patient populations and longer treatment durations.³

The TRIUMPH-1 study forms part of Lilly’s broader Phase 3 development program evaluating retatrutide across obesity, cardiovascular disease, obstructive sleep apnea, osteoarthritis pain, and metabolic dysfunction-associated steatotic liver disease.¹

What could retatrutide mean for the future obesity market?

Additional detailed findings from TRIUMPH-1 are expected to be presented at the upcoming American Diabetes Association Scientific Sessions.¹ Additional Phase 3 readouts from the TRIUMPH program are anticipated later this year.

Competition in the obesity therapeutics market continues to intensify as pharmaceutical companies expand development of next-generation incretin and multi-agonist therapies targeting both weight reduction and cardiometabolic health outcomes.⁴

References

1. Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. (2026 May 21). Eli Lilly. https://investor.lilly.com/news-releases/news-release-details/lillys-triple-agonist-retatrutide-delivered-powerful-weight
2. Jastreboff A. M. et al. (2023 Jun 26). Triple–Hormone-Receptor Agonist Retatrutide for Obesity. New England Journal of Medicine. https://www.nejm.org/doi/full/10.1056/NEJMoa2301972
3. Obesity Drug Development and the Expanding GLP-1 Market. BioPharm International. Accessed May 21, 2026. https://www.biopharminternational.com/search?biopharn_sanity_data%5Bquery%5D=obesity%20drug%20development
4. Bilodeau, K. (2026 May 19). Race intensifies to lead next wave of obesity drugs as trial results loom. PharmaVoice. https://www.pharmavoice.com/news/obesity-weight-loss-drug-trial-readout-pfizer-lilly-viking/820435/