A new triple-action weekly jab for type 2 diabetes could significantly reduce blood sugar and body weight, according to phase 3 trial results.

Patients in the trial receiving weekly retatrutide injections for 40 weeks lost more than four times as much weight as those on placebo, while the average drop in long-term blood sugar (HbA1c) was more than twice that of the placebo.

The triple hormone drug mimics three gut hormones that help control your appetite, blood sugar and metabolism: GLP-1, GIP and glucagon. Unlike other diabetes medications such as Ozempic and Wegovy, which primarily target the GLP-1 pathway to suppress appetite, or Mounjaro, which contains GLP-1 plus GIP to control blood-sugar levels, retatrutide also engages the glucagon receptor, which helps increase energy expenditure.

In the trial, published in the Lancet, 930 adults with type 2 diabetes were randomly assigned to receive 4mg, 9mg or 12mg of retatrutide, or placebo. None were already taking diabetes medicines, while all had inadequately controlled blood-sugar levels and BMIs of at least 23.

Blood-sugar levels (HbA1c), weight, cholesterol levels and other health markers were monitored, while any side-effects were recorded.

After 40 weeks, the average drop in HbA1c was about 1.7-1.9 percentage points for participants receiving retatrutide, compared with 0.8 with the placebo. Participants also lost on average about 11.5% to 15.3% of body weight on retatrutide, versus 2.6% with the placebo. Cholesterol and blood pressure also improved for those on the drug.

Fourteen participants experienced serious adverse events during the trial, including two in the placebo group, but for most participants, side-effects were mild to moderate and eased with time, with gastrointestinal symptoms the most commonly experienced.

The authors say this new triple-action medication has the potential to improve health outcomes for some patients, including greater weight loss, especially for those who may require more intensive treatment regimens to manage their type 2 diabetes. Further clinical trials are continuing.

The findings follow results from the manufacturer, Eli Lilly, suggesting retatrutide was highly effective in reducing weight among patients with obesity.

Dr Kath McCullough, special adviser on obesity at the Royal College of Physicians, said the findings were very encouraging.

“For many people living with diabetes and obesity, treatments like this could be genuinely life-changing,” she said.

“However, medications are not a silver bullet. While they are proving to be effective, the long-term goal must be to prevent people from needing them in the first place.”

Dr Marie Spreckley, a specialist in prevention of diabetes and related metabolic disorders at IMS Epidemiology, University of Cambridge, said the results were striking: “The magnitude of weight loss observed is particularly notable. However, because this study compared retatrutide with placebo rather than semaglutide or tirzepatide, it is not possible to determine from this data whether retatrutide is superior, equivalent or inferior to currently available therapies. Direct head-to-head trials will be required before firm conclusions can be drawn regarding comparative effectiveness.”

But she said weight loss alone did not necessarily equate to optimal health outcomes and patients needed support to maintain adequate nutritional intake, preserve muscle mass and maximise long-term health during treatment.

Dr Lucy Chambers, the head of research impact and communications at Diabetes UK, said: “These encouraging findings show that this new class of drug for type 2 diabetes could deliver dual benefits for both weight loss and blood-sugar management. We look forward to further research to understand its long-term effects and how it compares to treatments already available on the NHS.”