US researchers at the Los Angeles Institute for Metabolic Research found the experimental fat jab retatrutide helped overweight adults with type 2 diabetes shed up to a quarter of their body weight.
Results from the TRIUMPH-2 phase 3 clinical trial show the injection, nicknamed Godzilla and triple G, surpassed existing weight loss medications including Mounjaro while significantly improving blood pressure, cholesterol, and blood sugar control.
The drug, commonly known as Reta, is currently undergoing clinical trials. Experts have hailed the compound as a potential game changer for weight loss, heart disease, and osteoarthritis.
Investigators found that nearly a third of patients receiving the highest dose lost at least 25 per cent of their body weight over an 18-month period. By comparison, Mounjaro, currently the most powerful licensed weight loss drug available, helps users lose an average of 20.9 per cent of body weight over 16-and-a-half months.
Retatrutide functions as a triple agonist, targeting three distinct hormone pathways involved in appetite regulation to help the body burn fat, including GLP-1. This mechanism incorporates two more hormone pathways than Wegovy and one more than Mounjaro, which is presently available on the National Health Service (NHS) for patients with the highest clinical need.
Clinical trial results and weight loss impact
The latest findings stem from the TRIUMPH-2 trial, a phase 3 study evaluating the safety and effectiveness of retatrutide in 1,152 overweight and obese adults diagnosed with type 2 diabetes. Type 2 diabetes is a chronic metabolic condition characterized by high blood sugar levels, and patients with the condition typically lose less weight on obesity jabs than people without it.
Study participants from eight countries were randomly assigned to receive weekly injections of retatrutide at doses of 4mg, 9mg, or 12mg, or a placebo, alongside standard diet and exercise advice.
On average, participants had lived with obesity for more than two decades and had been diagnosed with type 2 diabetes at least five years before the trial started.
After 80 weeks of treatment, patients taking the strongest 12mg dose lost nearly a fifth of their body weight on average. Participants on the 9mg dose achieved a 17 per cent weight reduction, while those on the 4mg dose lost 12 per cent. Patients in the placebo group lost 5 per cent of their weight through diet and exercise alone.
Among those on the highest 12mg dose, almost half lost at least 20 per cent of their body weight, and nearly one in three achieved a weight loss of 25 per cent or more. For a typical obese man standing 5ft 10in tall, the average weight reduction seen on the highest dose equals roughly 23kg, or more than three-and-a-half stone, over 18 months.
Blood sugar control and health benefits
Beyond weight reduction, retatrutide demonstrated substantial improvements in blood sugar management. Trial data revealed that the drug dramatically lowered blood sugar levels, helping patients control diabetes and, in some cases, pushing the condition into remission.
Nearly three quarters of patients on the highest dose achieved blood sugar levels at or below the target used to diagnose diabetes. In contrast, only 29 per cent of participants given a placebo reached that level.
Participants also showed significant improvements across other cardiovascular risk factors, including reductions in bad cholesterol, blood pressure, and inflammation markers.
Presenting their findings at the Annual Meeting of The European Association for the Study of Diabetes (EASD) in Milan, Italy, the study authors concluded: "Retatrutide may advance the treatment of obesity and type 2 diabetes, a population where weight reduction has been challenging to achieve."
The authors added that the safety profile of the drug is generally similar to other weight loss jabs. Further research is expected to determine whether these health benefits translate to improvements in other obesity-related complications such as sleep apnoea, strokes, heart disease, and cancer.
Side effects, warnings and unauthorized sales
Like all other GLP-1 weight loss jabs, retatrutide was found to cause a number of side effects, including nausea and diarrhoea.
Abnormal skin sensations, including burning and discomfort, occurred in 7 per cent of participants taking the highest 12mg dose.
Seven deaths also occurred over the course of the 80-week study. However, trial investigators evaluated the fatalities and deemed them unrelated to the treatment.
The latest findings follow a surge in public interest surrounding retatrutide after early-stage trials suggested it might result in more significant weight loss than Ozempic and Mounjaro.
Eli Lilly, the pharmaceutical firm behind retatrutide, was forced to issue warnings against trying to obtain the drug via social media. The company stated that individuals using fake drugs from unauthorized sources are putting their health at "serious risk" and threatened to take legal action against sellers.
Earlier this year, the Daily Mail revealed that a man in his thirties died after taking an unapproved version of the drug, with dozens more having suffered serious side effects.
Since 2025, the UK Medicines and Healthcare products Regulatory Agency (MHRA) has recorded 77 reports of suspected retatrutide side effects. The regulatory agency added that yellow-card reports alone do not prove that a medicine caused the suspected adverse reaction.
Retatrutide is not currently approved or available on the NHS. However, experts say the treatment could be available to buy and even be prescribed on the NHS within three years if approved by health regulators.
Alternative obesity treatments in development
Separate research presented at the EASD conference found an experimental drug called petrelintide could offer similar weight loss to Mounjaro, but with fewer side effects than existing blockbuster jabs.
Rather than targeting GLP-1 hormones that regulate appetite and slow digestion, petrelintide mimics the hormone amylin, helping people feel fuller for longer.
Trial participants taking petrelintide lost around 10 per cent of their body weight in under 10 months, while also seeing improvements in blood pressure and cholesterol levels.
Experts say the main attraction of petrelintide is its tolerability, with users suffering far less unpleasant digestive side effects than typically seen with GLP-1 treatments.
Scientists not involved in the study noted that further research is needed, including a direct head-to-head comparison with Mounjaro and Wegovy, to support these claims.
