A new generation of weight-loss medicines is moving closer to doctors' clinics. Detailed results from TRIUMPH-2, a large phase 3 trial of the experimental drug retatrutide, were published in The Lancet on 29 September 2026 and presented at the European Association for the Study of Diabetes (EASD) annual meeting in Milan. In adults with both obesity and type 2 diabetes, the once-weekly injection led to substantial weight loss and better blood sugar control over 80 weeks.
Retatrutide is still investigational. It has not been approved for sale, and its maker says it cannot legally be sold or marketed for human use.
What is retatrutide?
Retatrutide, developed by Eli Lilly, is described as a "triple agonist". A single molecule activates the body's receptors for three hormones involved in appetite, blood sugar and energy use:
- GLP-1, the target of drugs such as semaglutide
- GIP, which tirzepatide also targets alongside GLP-1
- glucagon, a hormone that researchers think may help increase the energy the body uses
The idea is that hitting all three pathways could produce more weight loss than drugs acting on one or two.
Who was in the trial
According to The Lancet paper, TRIUMPH-2 randomly assigned 1,152 adults with obesity or overweight and type 2 diabetes to one of three dose levels of retatrutide or a placebo, given as a weekly injection. Participants had an average age of about 55, an average body mass index (BMI) of 38.2 and an average HbA1c, a measure of long-term blood sugar, of 7.7%. Most were already taking oral diabetes medicines. About 84% completed the study drug.
The headline results
The results can be reported in two ways, and both are useful:
- Counting everyone as randomised, including people who stopped treatment, average weight loss at 80 weeks was 11.9%, 16.8% and 18.8% across the three retatrutide doses, compared with 5.1% on placebo, according to the Lancet abstract.
- Estimating the effect if everyone had stayed on treatment, the measure highlighted by Lilly, average weight loss was 12.7%, 19.1% and 20.8%, compared with 4.0% on placebo.
At the highest dose, Lilly says 59.5% of participants no longer met the BMI criteria for obesity by the end of the study.
Blood sugar improved too. HbA1c fell by an average of 1.4 to 1.6 percentage points with retatrutide, compared with 0.2 points on placebo. Lilly reports that up to about 40% of participants in the higher-dose groups reached an HbA1c below 5.7%, which is in the normal range, although this analysis was not adjusted for multiple comparisons. The company also reported falls in triglycerides, blood pressure and waist size at the highest dose.
Why the diabetes result matters
Weight loss is usually harder to achieve in people with type 2 diabetes. A Lancet commentary on the trial notes that GLP-1 drugs generally produce less weight loss in people with diabetes than in people without diabetes who have a similar BMI. It also notes that phase 3 trials of retatrutide in people with obesity but no diabetes have reported weight losses of up to 28.3%.
So while the TRIUMPH-2 figures are lower than those headline numbers, they are large for this group of patients.
Side effects
As with other medicines in this family, stomach and gut side effects were the most common. Lilly reports that across the three doses compared with placebo:
- diarrhoea affected about 27–34% of participants, compared with 13%
- nausea affected about 14–28%, compared with 8%
- constipation, reduced appetite and vomiting were also more common
Abnormal skin sensations, known as dysesthesia, were reported by 4.5–7.3% of people on retatrutide, compared with 0.7% on placebo. Lilly says most side effects were mild to moderate. The share of people who stopped treatment because of side effects ranged from 3.8% to 11.6% on retatrutide, compared with 4.9% on placebo.
Longer-term safety, and whether the drug reduces heart attacks, strokes or other complications, is still being studied.
When could it be available?
Lilly says it plans to submit an application to the US Food and Drug Administration in the first quarter of 2027. Regulators in other countries, including India, would need to make their own decisions. Any approval timeline is uncertain.
A word of caution
Because retatrutide is still investigational and Lilly says it cannot be legally sold, anything offered online under that name is not an approved medicine, and its contents and safety cannot be assured.
If you are living with obesity or type 2 diabetes:
- Talk to your doctor about approved treatment options suited to your health.
- Do not buy injections online or from unofficial sellers.
- Do not stop or change your diabetes medicines without medical advice.
- Remember the basics. Diet, physical activity, sleep and regular check-ups remain central to managing both conditions, with or without medicines.
FAQ
Is retatrutide approved? No. It is an investigational drug. Lilly plans to apply to the US FDA in early 2027.
How much weight did people lose? On average, between about 12% and 21% of body weight over 80 weeks depending on dose and how results are calculated, compared with 4–5% on placebo.
Is retatrutide the same as Ozempic or Mounjaro? No. It acts on three hormone receptors (GLP-1, GIP and glucagon), whereas semaglutide acts on one and tirzepatide on two.
What were the main side effects? Mostly gut-related, including diarrhoea, nausea, constipation and vomiting.
Sources
- The Lancet: Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2), phase 3 trial
- The Lancet comment: Retatrutide in adults with obesity and type 2 diabetes, what have we learned from TRIUMPH-2?
- Eli Lilly via PR Newswire: TRIUMPH-2 results (29 September 2026)
- AJMC: Retatrutide yields up to 20.8% weight loss in obesity with T2D
