Eli Lilly’s experimental drug retatrutide helped obese patients shed close to a third of their body weight in a major clinical trial, a result the company calls the strongest ever recorded for a weight-loss medicine.
Story Snapshot
- The highest dose of retatrutide cut body weight by an average of 70.3 pounds, or 28.3%, over 80 weeks.
- A second trial found similar results in patients who also have type 2 diabetes.
- Nearly half of high-dose patients lost 30% or more of their body weight, a range once tied only to surgery.
- Eli Lilly plans to ask federal regulators to approve the drug in early 2027.
- Up to 11% of patients on the top dose dropped out of the trial due to side effects.
Drug Hits Surgery-Level Weight Drops
Eli Lilly announced results from TRIUMPH-1, a Phase 3 trial testing retatrutide against a placebo in adults with obesity. Participants who took the 9 mg dose lost an average of 64.4 pounds, or 25.9% of their body weight. Those on the 12 mg dose lost 70.3 pounds, or 28.3%, over 80 weeks. Placebo patients lost just 2.2%, according to the company’s data on those who stayed on treatment.
The trial included roughly 2,500 people with a body mass index that put most in the severe obesity category. Lilly reported that all three doses tested met the study’s main goals, showing the drug worked across a range of starting weights and body sizes.
Diabetes Patients Also See Gains
A related trial called TRIUMPH-2 tested retatrutide in adults with both obesity and type 2 diabetes. Every dose group in that study lost significant weight while also showing better blood sugar control, meeting the trial’s combined goals for weight and glucose management. That matters because diabetes and obesity often make each other harder to treat.
Researchers built retatrutide to act on three different hormone receptors at once, targeting GLP-1, GIP, and glucagon pathways. Earlier Phase 2 testing found weight loss up to 24.2% at 48 weeks, so the new Phase 3 numbers push that signal even higher over a longer stretch of treatment.
Weight Loss Rivals Surgical Results
Company figures show about 45% of patients on the 12 mg dose lost 30% or more of their body weight, a level of weight loss historically seen mainly after bariatric surgery. Some patients lost as much as 85 pounds during the study, according to reporting on Lilly’s release.
TRIUMPH-1 is striking on several fronts. In the phase 3 results @NEJM just posted, retatrutide delivered substantial weight loss and also reduced knee osteoarthritis pain and obstructive sleep apnea events for the people who had those problems.
It is also a great chance to learn… https://t.co/Bai0OsS1ih
— Çağrı Mert Bakırcı (@cagrimbakirci) September 30, 2026
The gains came with real trade-offs. Discontinuation rates due to side effects hit 4.1%, 6.9%, and 11.3% for the 4 mg, 9 mg, and 12 mg groups, compared with 4.9% on placebo. Those numbers show that stronger results also came with a higher chance patients could not tolerate the treatment long enough to finish it.
What Happens Next
Lilly said in July that two more Phase 3 trials of retatrutide also produced positive results and that the company plans to file for federal approval in the first quarter of 2027. The company is racing against its own existing drugs, including Zepbound, as well as rivals, to hold its lead in the fast-growing obesity treatment market.
Detailed results from these trials are still headed for peer-reviewed publication, which will let outside scientists check Lilly’s numbers and methods in full. For the millions of Americans already struggling with the cost and availability of weight-loss shots, the bigger question ahead may not be whether the drug works, but who can actually afford it once it reaches pharmacy shelves.
Sources:
time.com, investor.lilly.com, theguardian.com, cnbc.com
