Retatrutide Exhibits Meaningful Weight Loss in Phase 3 Trial

Eli Lilly released topline results from its TRIUMPH-1 phase 3 clinical trial, highlighting that retatrutide 12 mg achieved an average weight loss of 70.3 pounds over 80 weeks, according to a news release.¹ With over 45% of trial participants exhibiting at least 30% weight loss, the investigational therapy has potential to become the first-in-class GIP, GLP-1, and glucagon triple hormone receptor agonist for obesity management.

“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, professor of medicine & pediatrics at the Yale School of Medicine, director of the Yale Obesity Research Center, and lead trial investigator, according to the release. “It was impressive to see that every dose of retatrutide resulted in clinically meaningful weight reduction for nearly all participants.”

The clinical significance of these findings was further shown by the trial’s extension period for participants with a baseline body mass index (BMI) of 35 or higher. In this specific subgroup, individuals reaching 104 weeks of treatment achieved a mean weight reduction of 30.3%, or approximately 85 pounds.¹

These data suggest a continuing weight loss trajectory, aligning with earlier Phase 2 observations where weight reduction curves had not yet reached a plateau even after 48 weeks of treatment.^2,3

For pharmacists, these results represent a shift toward pharmacological weight reduction levels traditionally associated with bariatric surgery.^1,2

READ MORE: Early Responders With Oral Semaglutide Indicate Long-Term Weight Loss

The therapeutic efficacy of retatrutide is driven by its unique mechanism as a unimolecular agonist at the GIP, GLP-1, and glucagon receptors. While GLP-1 and GIP primarily regulate satiety and glucose-dependent insulin secretion, the addition of glucagon receptor agonism is designed to increase energy expenditure and stimulate lipid catabolism.

This triple-hormone approach aims to overcome the metabolic adaptations that often hinder long-term weight management. Interestingly, phase 2 data also noted that women may achieve a higher mean weight reduction than men, a factor for pharmacists to consider during individualized treatment evaluations.^2,3

As these advanced incretin-based therapies enter the clinical landscape, the Obesity Association—part of the American Diabetes Association—has released new standards of care for obesity medications. These 2026 guidelines emphasize a person-centered, shared decision-making approach between health care providers and patients.^4,5

Clinical pharmacists are integral to this process, utilizing the Pharmacists’ Patient Care Process to assess patient eligibility, provide counseling on proper administration, and optimize dosing strategies. Pharmacists are also tasked with managing the most common adverse events, which in the TRIUMPH-1 trial were primarily gastrointestinal, including nausea, diarrhea, and vomiting.^1,3,5

Notably, the trial observed that the 4 mg dose achieved nearly 20% weight loss with lower discontinuation rates compared with higher doses, offering a potential strategy for balancing efficacy and tolerability.¹

Despite the clinical promise, pharmacists must navigate significant barriers to treatment, particularly regarding cost and insurance coverage. Currently, Medicare is prohibited from covering pharmacotherapy for weight loss when used specifically for obesity management.⁵

Furthermore, clinical pharmacy networks and the Obesity Association have issued strong warnings against the use of non-FDA-approved compounded products. Federal enforcement discretion regarding compounded versions of these medications ended in mid-2025 as supply began to stabilize, highlighting the pharmacist's role in advocating for the use of authorized, evidence-based therapies.^4,5

Pharmacists also play a critical role in perioperative safety for patients taking these therapies. Recent safety signals have identified a risk of pulmonary aspiration during surgery for patients under deep sedation or anesthesia, necessitating careful medication withholding before procedures.^1,5

By monitoring for long-term safety concerns and promoting strategies to preserve muscle mass, such as resistance training and protein intake, pharmacists ensure a comprehensive approach to chronic disease management.⁵

As retatrutide moves toward potential regulatory approval, it offers a transformative tool for addressing the complex biology of obesity and improving long-term health trajectories.^1,2,5

“Importantly, treatment with retatrutide not only resulted in robust weight reduction, but also in clear improvements in assessed cardiometabolic health measures,” concluded Jastreboff, according to the release.¹ “For patients I see in clinic, retatrutide may potentially be a highly impactful future tool to treat their obesity and transform their health.”

READ MORE: Obesity Management Resource Center

REFERENCES

1. Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. News Release. Eli Lilly and Company. May 21, 2026. Accessed May 21, 2026. https://investor.lilly.com/news-releases/news-release-details/lillys-triple-agonist-retatrutide-delivered-powerful-weight-loss

2. Jakubowska A, Roux CWL, Viljoen A. The Road towards triple agonists: glucagon-like peptide 1, glucose-dependent insulinotropic polypeptide and glucagon receptor - an update. Endocrinol Metab (Seoul). 2024 Feb;39(1):12-22. doi: 10.3803/EnM.2024.1942.

3. Jastreboff AM, Kaplan LM, Frias JP, et al. Triple–hormone-receptor agonist retatrutide for obesity — a phase 2 trial. N Engl J Med. 2023;389(6):514-526. https://doi.org/10.1056/nejmoa2301972

4. The Obesity Association publishes new standards of care section on obesity medications. American Diabetes Association. January 13, 2026. Accessed May 21, 2026. https://diabetes.org/newsroom/press-releases/obesity-association-publishes-new-standards-care-section-obesity

5. Lingow S, Carris N, Clements J, et al. The pharmacist’s role in the use of incretin‐based therapies for weight management: an opinion of the Endocrine and Metabolism Practice and Research Network of the American College of Clinical Pharmacy. JACCP. 2025;8(10):1078-1093. https://doi.org/10.1002/jac5.70111