An experimental weight-loss drug cut body weight by 18.8 per cent in adults with obesity and type 2 diabetes, showing substantial weight loss while raising questions about intensive treatment. Retatrutide is not approved by any regulatory agency.

The highest dose produced that reduction over 80 weeks in the TRIUMPH-2 trial. Participants also received dietary counselling and exercise guidance, making the result notable in a population that has generally experienced less weight loss with obesity medications than people without diabetes.

Weight Loss Reached 18.8 Per Cent

Weekly retatrutide injections of 4mg, 9mg and 12mg produced average weight losses of 11.9 per cent, 16.8 per cent and 18.8 per cent, respectively. Those receiving placebo lost 5.1 per cent, according to the phase 3 trial in The Lancet.

At the highest dose, 47 per cent of participants lost at least 20 per cent of their starting weight, while 31 per cent lost at least 25 per cent. With placebo, the figures were 6 per cent and 3 per cent.

The trial screened 2,047 people across eight countries, with 1,152 adults randomly assigned to retatrutide or placebo. It focused on adults with obesity and type 2 diabetes, who can struggle to achieve substantial weight reduction.

Retatrutide mimics three gut hormones involved in appetite, blood glucose and metabolism: GLP-1, GIP and glucagon. Unlike Wegovy and Mounjaro, it also targets the glucagon receptor, which may increase energy expenditure.

A separate phase 3 trial, TRIUMPH-1, found up to 28.3 per cent weight loss over 80 weeks in people with obesity. Its findings appeared in the New England Journal of Medicine.

Randy Seeley, a University of Michigan professor not involved in TRIUMPH-2, said people with type 2 diabetes tend to lose less weight with GLP-1 drugs. He has previously been a paid consultant for Eli Lilly.

Blood Glucose Also Improved

Read more

Some 72 per cent of participants achieved an HbA1c of 6.5 per cent or lower, compared with 29 per cent on placebo. HbA1c reflects average blood glucose levels over roughly two to three months, indicating longer-term glucose control.

Retatrutide also improved blood pressure and lipid profiles and lowered high-sensitivity C-reactive protein, a marker of inflammation. Researchers said its safety profile was similar to other GLP-1 receptor agonists.

Gastrointestinal problems were the most frequently reported adverse events. Diarrhoea affected 27 to 34 per cent of retatrutide participants, compared with 13 per cent on placebo, while nausea affected 14 to 28 per cent, versus 8 per cent.

Seven deaths occurred during the trial, including one in the placebo group. Investigators judged all seven deaths to be unrelated to the study intervention, according to the trial findings.

Seeley cautioned that intense weight loss can raise the risk of gallstones and micronutrient deficiencies. Very low calorie intake can also make it harder to obtain enough essential nutrients, he said.

Drug Remains Experimental

Professor Giles Yeo, an obesity scientist at the University of Cambridge, warned that the drug's strength could pose risks for people who do not need it. He said people with eating disorders or body dysmorphia could face greater danger.

Eli Lilly says retatrutide is legally available only through its clinical trials. The company warns that products sold outside those trials cannot be verified for safety, purity or dosing.

Eli Lilly plans to submit the data to the US Food and Drug Administration and other regulators in the first quarter of 2027. Daniel Skovronsky, the company's chief scientific and product officer, said the results set a new 'high-water mark' for weight loss.

Read more