Important Disclaimer
This article is for educational and informational purposes only. Retatrutide is an investigational medication and has not been approved for use in the United Kingdom or any other country as of July 2026. The information below is based on publicly available data from clinical trials. It is not medical advice. Retatrutide should only be used within approved clinical trial settings under medical supervision. Research peptides and investigational compounds are intended strictly for laboratory research use and are not for human consumption. Always consult a qualified healthcare professional before considering any treatment.
Note on Sources: This article is based on publicly available clinical trial information as of July 2026. It has been prepared with reference to primary sources released by Eli Lilly and Company.
Overview of Retatrutide
Retatrutide is an investigational once-weekly injectable medication being developed by Eli Lilly. It is a triple hormone receptor agonist that targets GLP-1, GIP, and glucagon receptors. This mechanism is different from currently approved medications such as semaglutide and tirzepatide.
In 2026, Eli Lilly released results from the Phase 3 TRIUMPH-1 clinical trial. These results, along with additional data presented at the American Diabetes Association Scientific Sessions in June 2026, have provided more clarity on the potential effects of retatrutide.
Key Results from the TRIUMPH-1 Trial
The TRIUMPH-1 trial studied retatrutide in adults with obesity or overweight who had at least one weight-related health condition but did not have diabetes. Participants received retatrutide at doses of 4 mg, 9 mg, or 12 mg once weekly, or a placebo, for 80 weeks.
At 80 weeks, the average weight loss was:
- 19.0% with the 4 mg dose
- 25.9% with the 9 mg dose
- 28.3% with the 12 mg dose [1]
In a smaller group of participants who continued treatment in an extension study, those on the 12 mg dose achieved an average weight loss of 30.3% by week 104 [1].
A significant number of participants on the highest dose also saw improvements in other areas. For example, 65.3% of participants on the 12 mg dose achieved a BMI below 30 at 80 weeks. The trial also reported improvements in waist circumference and certain cardiovascular risk markers, such as triglycerides and systolic blood pressure.
Additional data presented in June 2026 showed reductions in knee osteoarthritis pain and improvements in obstructive sleep apnea severity among participants who had these conditions [2].
Safety and Side Effects
Like other medications in this class, retatrutide was associated with gastrointestinal side effects. The most common side effects reported in the TRIUMPH-1 trial included nausea, diarrhoea, vomiting, and constipation. These effects were more frequent during dose increases and were generally more common at higher doses.
Discontinuation rates due to adverse events were 4.1% for the 4 mg dose, 6.9% for the 9 mg dose, and 11.3% for the 12 mg dose, compared with 4.9% for placebo [1]. These figures indicate that while many participants tolerated the medication, side effects led some people to stop treatment, particularly at the highest dose.
Long-term safety data beyond the study periods is still being collected through ongoing trials.
What the Data Means in Practical Terms
The TRIUMPH-1 results show that retatrutide can produce substantial average weight loss in a clinical trial setting. The weight loss observed at the 12 mg dose approaches levels typically seen with bariatric surgery. The trial also suggested potential benefits beyond weight loss, including improvements in knee pain and sleep apnea.
However, several important points should be considered:
- These results come from a controlled clinical trial with specific inclusion criteria and support for participants.
- Individual results can vary significantly.
- Side effects, particularly gastrointestinal issues, were common and led to treatment discontinuation in some cases.
- Retatrutide remains an investigational treatment and is not currently approved or available for general use.
Current Status and Future Outlook
As of July 2026, retatrutide has not been submitted for regulatory approval. Industry expectations suggest that Eli Lilly may submit a New Drug Application to the U.S. Food and Drug Administration in the fourth quarter of 2026. Additional results from other trials in the TRIUMPH programme are expected later in 2026. Any potential approval would depend on the outcome of the regulatory review process.
For now, retatrutide is only available to people participating in clinical trials.
Summary
The 2026 Phase 3 data provides important information about retatrutide’s potential effects on weight and certain obesity-related conditions. While the results are notable, retatrutide is still in the later stages of clinical development. Individuals exploring weight management options should speak with their healthcare provider about currently approved treatments and monitor updates from reliable medical sources as more data becomes available.
References
- Eli Lilly and Company. (2026, May 21). Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. https://investor.lilly.com/news-releases/news-release-details/lillys-triple-agonist-retatrutide-delivered-powerful-weight-loss
- Eli Lilly and Company. (2026, June). Additional TRIUMPH-1 data presented at the American Diabetes Association 86th Scientific Sessions. Data presented at ADA 2026.
- ClinicalTrials.gov. A Study of Retatrutide (LY3437943) in Participants With Obesity or Overweight (TRIUMPH-1). https://clinicaltrials.gov/study/NCT05929066