Archive · 3 Oct 2026
Retatrutide Produces Up to 25% Weight Loss in Phase 3 Trial
Researchers tested a new weight-loss medicine called retatrutide.
The study included 2,339 adults with obesity who did not have diabetes.
People received weekly injections of different doses or a placebo, which contains no active study medicine.
After 80 weeks, people taking the highest dose lost an average of 25% of their starting weight.
Some people taking it also had fewer breathing problems during sleep or less knee pain.
A smaller group who continued on the highest dose had lost an average of 29.9% after 104 weeks.
Stomach and digestive problems were common, and some people stopped taking the medicine.
The study did not compare retatrutide directly with other weight-loss drugs or establish its cardiovascular safety.
In a Phase 3 trial of 2,339 adults with obesity who did not have diabetes, weekly retatrutide injections were compared with placebo.
After 80 weeks, average weight loss was 25% with the 12 mg dose, 23.7% with 9 mg, and 17.6% with 4 mg; the placebo group lost 3.9%.
Participants with knee osteoarthritis taking the highest dose had greater knee-pain reduction than those given placebo.
For participants with obstructive sleep apnoea, breathing disruptions fell by 32.1 episodes per hour with 12 mg, compared with 9.6 with placebo.
Nausea affected about 42% of those on the highest dose, and 11% stopped treatment because of adverse events, versus 4.6% on placebo.
- Who
- Eli Lilly is developing retatrutide; researchers studied 2,339 adults with obesity who did not have diabetes.
- What
- A Phase 3 trial reported weight loss and other health outcomes with retatrutide compared with placebo.
- When
- The main results were measured after 80 weeks; a smaller extension group was followed for 104 weeks.
- Why
- The trial evaluated retatrutide as a treatment for obesity and examined some associated health problems.
- Trial size
- 2,339 adults with obesity and without diabetes
- Treatment period
- 80 weeks for the main trial results
- Highest-dose weight loss
- Average 25% of starting body weight with 12 mg
- Other doses
- Average weight loss was 23.7% with 9 mg and 17.6% with 4 mg
- Placebo weight loss
- Average 3.9% after 80 weeks
- Extension results
- In a smaller group of 532 participants, average loss among those initially receiving 12 mg reached 29.9% after 104 weeks
- Common side effect
- About 42% of participants receiving 12 mg reported nausea
- Publication and funding
- Published in The New England Journal of Medicine; Eli Lilly funded the research and participated in collecting and analysing data