A new “Godzilla” weight-loss injection could challenge Mounjaro after research found it helped some users lose up to a quarter of their body weight while also improving blood pressure and cholesterol.
US researchers say retatrutide may be the most effective treatment yet for people who are overweight or obese and have type 2 diabetes—a group that generally loses less weight with existing blockbuster injections than patients without the condition.
Often shortened to “Reta”, the drug remains in clinical development but is already being described as a potential game changer for weight management, cardiovascular health and osteoarthritis.
Researchers at the Los Angeles Institute for Metabolic Research found that almost one in three patients receiving the highest dose lost at least 25 per cent of their body weight over 18 months.
Mounjaro, currently considered the most powerful licensed weight-loss medicine, produces an average reduction of about 20.9 per cent when used for 16 and a half months.
Retatrutide, also known as “triple G”, is a triple agonist. It works through three hormone pathways linked to appetite and fat burning, including GLP-1.
That gives it two more targets than Wegovy and one more than Mounjaro, which is already available through the NHS for patients judged to have the greatest need.
The results come from TRIUMPH-2, a phase 3 trial examining retatrutide’s safety and effectiveness in 1,152 adults with type 2 diabetes who were overweight or obese.
The triple-action drug could be available on the NHS within three years
Participants from eight countries were randomly given weekly injections containing 4mg, 9mg or 12mg of retatrutide, or a placebo. All groups also received advice on diet and exercise.
On average, those taking part had lived with obesity for more than 20 years and had been diagnosed with type 2 diabetes at least five years before entering the study.
After 80 weeks, people given the 12mg dose had lost almost a fifth of their body weight on average. The corresponding figures were 17 per cent for the 9mg dose and 12 per cent for the 4mg dose.
Almost half of those on the highest dose lost at least 20 per cent of their weight, while close to one in three achieved a reduction of at least 25 per cent.
By comparison, participants who received the placebo lost just 5 per cent through diet and exercise alone.
For an obese man measuring 5ft 10in, the average loss recorded with the highest dose would be equivalent to about 23kg—or more than three and a half stone—over 18 months.
The injection also produced a marked improvement in blood sugar control. Some patients were able to manage their diabetes more effectively, while others saw the condition enter remission.
Nearly three quarters of patients receiving 12mg reached blood sugar levels at or below the threshold used to diagnose diabetes. That compared with just 29 per cent in the placebo group.
The trial also recorded significant gains in other cardiovascular risk measures, including levels of harmful cholesterol and inflammation.
However, retatrutide was not free from the side-effects associated with other GLP-1 injections. Nausea and diarrhoea were among the problems reported by participants.
Abnormal skin sensations, such as burning and general discomfort, were reported by 7 per cent of people receiving the highest dose.
Seven deaths also occurred over the course of the study, which were deemed unrelated to the treatment by investigators.
Presenting their findings at the Annual Meeting of The European Association for the Study of Diabetes (EASD) in Milan, the authors concluded: ‘Retatrutide may advance the treatment of obesity and type 2 diabetes, a population where weight reduction has been challenging to achieve.’
They added that the safety profile of the drug is generally similar to the other weight loss jabs.
Further research is expected to determine whether these benefits translate to improvements in other obesity-related complications such as sleep apnoea, strokes, heart disease and cancer.
The latest findings follow a surge in interest in the drug after early-stage trials suggested it may 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.
Eli Lilly were forced to issue warnings when promising results from early stage trials led to a surge in people trying to obtain the drug through social media
The company said those using fake drugs from unauthorised sources are putting their health at ‘serious risk’ and threatened to take action against the sellers.
Earlier this year the Daily Mail revealed 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 Medicines and Healthcare products Regulatory Agency (MHRA), has recorded 77 reports of suspected retatrutide side effects – but added that reports alone do not prove that a medicine caused the suspected adverse reaction.
Retatrutide is not currently approved or available on the NHS, but could be available to buy and even be prescribed on the NHS within three years if approved by regulators, experts say.
Separate research presented at EASD 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 amyline, helping people feel fuller for longer.
Participants 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 its main attraction is its tolerability – with users suffering far less unpleasant digestive side effects than typically seen with GLP-1s.
Scientists not involved in the study said further research is needed, including a direct head-to-head comparison with Mounjaro and Wegovy, to support these claims.
