Retatrutide for Weight Loss: What the New Type 2 Diabetes Trial Found
Written and medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
A large new trial gives the clearest picture yet of retatrutide for weight loss in people who live with both type 2 diabetes and obesity. In the phase 3 TRIUMPH-2 study, published in The Lancet on September 29, 2026, adults taking the highest dose lost an average of 20.8% of their body weight over 80 weeks, compared with 4.0% on placebo, and their blood sugar (A1C) fell by up to 1.6 percentage points (Eli Lilly; The Lancet). Retatrutide is still experimental: it is not approved by the FDA, and versions sold online are not legal, tested medicines (FDA).
Key takeaways
TRIUMPH-2 is a phase 3, double-blind, placebo-controlled trial of 1,152 adults with type 2 diabetes and obesity or overweight, run for 80 weeks.
Average weight loss was 12.7% (4 mg), 19.1% (9 mg) and 20.8% (12 mg), versus 4.0% with placebo.
A1C fell by 1.4 to 1.6 percentage points with retatrutide, versus 0.2 with placebo. Up to 40% of people reached an A1C below 5.7%, the normal range.
The most common side effects were digestive: diarrhea, nausea, constipation and vomiting, mostly mild to moderate.
Retatrutide is not approved. The company plans to apply to the FDA in the first quarter of 2027.
The FDA warns that retatrutide sold "for research purposes" is unapproved and cannot legally be compounded.
What is retatrutide?
Retatrutide is an experimental once-weekly injection made by Eli Lilly. Most people know GLP-1 medicines such as semaglutide, and "dual" medicines such as tirzepatide. Retatrutide goes one step further. It is a "triple agonist": it acts on three hormone receptors at once, called GIP, GLP-1 and glucagon (Eli Lilly).
In simple terms, these hormones help control appetite, how full you feel, how your body handles sugar, and how it uses energy. Acting on all three is the reason researchers expect larger effects on weight than older drugs. That idea has to be proven in trials, which is why TRIUMPH-2 matters.
How was the retatrutide for weight loss trial designed?
TRIUMPH-2 is one of four large phase 3 trials in Lilly's TRIUMPH program. Here is how it worked (Eli Lilly):
Who took part: 1,152 adults with type 2 diabetes plus obesity or overweight. Their average starting weight was about 106 kg (234 lb), and their average A1C was 7.7%.
Groups: People were randomly placed into four equal groups: retatrutide 4 mg, 9 mg, 12 mg, or a placebo (dummy) injection, once a week.
Blinding: Neither participants nor study staff knew who received which treatment. This "double-blind" design reduces bias.
Dosing: Everyone started at 2 mg, and the dose went up step by step every four weeks to limit side effects.
Length: 80 weeks of treatment, then four weeks of follow-up.
This is the strongest kind of study for testing a medicine: large, randomized, blinded and placebo-controlled.
How much weight did people lose on retatrutide?
The results rose with the dose. The table below shows the main numbers (Eli Lilly).
Result at 80 weeks | Placebo | 4 mg | 9 mg | 12 mg |
|---|---|---|---|---|
Average weight loss | 4.0% | 12.7% | 19.1% | 20.8% |
Average weight loss (lb) | 9.3 | 29.8 | 45.4 | 49.6 |
Lost at least 15% of body weight | 6.4% | 36.6% | 62.2% | 67.0% |
Lost at least 20% of body weight | 1.5% | 24.0% | 45.3% | 52.0% |
Lost at least 25% of body weight | 0.8% | 10.8% | 30.6% | 34.9% |
At the 12 mg dose, about half of participants lost at least a fifth of their body weight, and 59.5% no longer met the BMI definition of obesity by the end of the trial.
One detail matters for reading these numbers. Lilly reported them using the "efficacy estimand." This method estimates what happens to people who keep taking the drug as prescribed. Results that count everyone, including people who stopped treatment, are usually somewhat smaller. The full paper in The Lancet reports both.
What happened to blood sugar and heart risk factors?
For people with type 2 diabetes, weight is only part of the story. Blood sugar control is just as important (Eli Lilly).
Blood sugar result | Placebo | 4 mg | 9 mg | 12 mg |
|---|---|---|---|---|
Change in A1C (percentage points) | −0.2 | −1.4 | −1.6 | −1.5 |
Reached A1C of 6.5% or lower | 26.3% | 73.1% | 79.2% | 79.0% |
Reached A1C below 5.7% (normal range) | 4.4% | 28.4% | 40.0% | 39.3% |
On the 12 mg dose, the company also reported lower triglycerides (−39.5%), lower non-HDL cholesterol (−19.6%), lower systolic blood pressure (−10.8 mmHg), a smaller waist (−6.7 inches) and lower hsCRP, a marker of inflammation (−58.3%).
These are risk factors, not outcomes. The trial did not show that retatrutide prevents heart attacks, strokes or deaths. That would need a dedicated long-term outcomes trial.
The lead investigator, Dr. Juan P. Frías, said that results like these "may change what we set out to achieve with a single therapy for adults living with type 2 diabetes and obesity" (Eli Lilly).
What are the side effects of retatrutide?
Side effects were mostly digestive, and they became more common at higher doses. Most were mild to moderate and settled during treatment (Eli Lilly).
Side effect | Placebo | 4 mg | 9 mg | 12 mg |
|---|---|---|---|---|
Diarrhea | 13.2% | 27.4% | 33.5% | 33.6% |
Nausea | 8.0% | 13.7% | 20.8% | 28.0% |
Constipation | 9.4% | 14.0% | 16.2% | 16.8% |
Vomiting | 4.2% | 5.5% | 10.2% | 15.7% |
Dysesthesia (unusual skin sensations) | 0.7% | 4.5% | 5.6% | 7.3% |
Stopped treatment due to side effects | 4.9% | 3.8% | 11.6% | 7.7% |
Two points stand out. First, dysesthesia, meaning unusual skin sensations such as tingling or sensitivity, was more common with retatrutide than with placebo. Second, about 1 in 9 people on the 9 mg dose stopped treatment because of side effects. Long-term safety beyond 80 weeks is still unknown.
Is retatrutide available, and is it safe to buy online?
No. Retatrutide is not approved by the FDA for any condition. Lilly says it plans to submit an application to the FDA in the first quarter of 2027 (Eli Lilly). A regulator then reviews the full data before any decision.
Some websites sell products labeled "retatrutide" as "for research purposes" or "not for human consumption." The FDA states that retatrutide has not been found safe and effective for any condition, cannot be used in compounding under federal law, and that it has warned companies selling these products (FDA). Products like these may contain the wrong dose, the wrong substance or contaminants. The only safe way to receive retatrutide today is inside a registered clinical trial.
What does this mean for you?
If you have type 2 diabetes and obesity, this trial is encouraging news for the future of retatrutide for weight loss and blood sugar control. It suggests a single weekly medicine may one day lower weight and blood sugar at the same time, for many people into the normal range.
For now, practical steps include:
Talk to your doctor about approved options. Several approved medicines already help with weight and blood sugar.
Avoid online "research" products. They are unapproved and untested.
Ask about clinical trials. If you are interested in new treatments, your doctor can help you look for a trial you may qualify for.
Keep the basics going. Nutrition, physical activity, sleep and regular check-ups remain the foundation of care, with or without medication.
Frequently asked questions
Is retatrutide for weight loss approved by the FDA?
No. Retatrutide is an experimental medicine and is not approved by the FDA. Its maker plans to apply for approval in the first quarter of 2027.
How much weight did people lose in the TRIUMPH-2 trial?
Over 80 weeks, average weight loss was 12.7%, 19.1% and 20.8% on the 4 mg, 9 mg and 12 mg doses, compared with 4.0% on placebo.
How is retatrutide different from semaglutide and tirzepatide?
Semaglutide acts on the GLP-1 receptor, and tirzepatide acts on GIP and GLP-1 receptors. Retatrutide acts on three: GIP, GLP-1 and glucagon receptors.
What are the most common side effects of retatrutide?
Diarrhea, nausea, constipation, vomiting and reduced appetite were the most common. They were mostly mild to moderate. Unusual skin sensations (dysesthesia) were also more common than with placebo.
Can I buy retatrutide online?
Products sold online as "retatrutide" are not approved medicines. The FDA has warned companies that sell them, and retatrutide cannot legally be compounded.
Health information, not medical advice
Health information, not medical advice. This article explains published research for general education. It does not replace advice from your own doctor. Never start, stop or change a medicine without talking to a qualified health professional.
Sources
Eli Lilly and Company. Lilly's triple agonist, retatrutide, delivered substantial weight loss and A1C reduction, underscoring its potential promise for people with obesity and type 2 diabetes. September 29, 2026.
The Lancet. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial. Published September 2026.
U.S. Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss. Updated September 1, 2026.
ClinicalTrials.gov. Study record NCT05929079 (TRIUMPH-2).
About the author: Dr. Baraa Alnahhal, MD, is a medical doctor and the founder of Rinnit. Dr. Baraa Alnahhal reviews new medical research and translates it into clear, evidence-based health information for everyday readers.
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