New once-a-week weight loss jab Tirzepatide sold as Mounjaro sees obese shed body fat, study finds

A new once-a-week obesity jab helps people shed large amounts of body fat, analysis suggests.

Tirzepatide, from Eli Lilly and Company and sold under the brand name Mounjaro, is currently approved by UK regulators for type 2 diabetes but may also soon be approved for obesity.

If the Medicines and Healthcare products Regulatory Agency (MHRA) grants a licence for its use to treat obesity, then the Scottish Medicines Consortium can consider whether it should be made available for routine use in Scotland.

The National Institute for Health and Care Excellence (NICE) is seeing whether the drug would be a good use of NHS funds in England before recommending or rejecting it for use across the health service south of the border.

In a new study, presented at the European Congress on Obesity in Dublin but not yet peer-reviewed, researchers conducted an analysis of 2,539 adults who were overweight or obese and had at least one weight-related complication, excluding diabetes.

They were split into groups to either receive a placebo drug, or 5mg, 10mg or 15mg doses of tirzepatide.

The proportion of people who lost weight compared with the start of the study, and those who lost more than 5% of their body weight in total, were assessed across BMI categories 27 to 30, 30 to 35, 35 to 40 and 40 and over.

Body composition was also evaluated in a smaller group who underwent specialised scans to look at their fat mass and their lean mass.

At the start of the study, people typically weighed more than 16st (104.8kg) and had a BMI of 38.

The average body weight loss after 72 weeks of weekly injections was 16% for the 5mg dose group, 21% for the 10mg and 23% for the 15mg group.

This compared with a 2% loss on placebo.

The proportion of people who lost 5% or more of their body weight was 89% on the 5mg dose, 96% on the 10mg and 96% with 15mg.

This compared with 28% on the placebo.

Furthermore, more than half of people (56%) in the 10mg group and 63% in the 15mg group lost a fifth or more of their body weight compared with 1% on placebo.

All doses of the drug led to weight loss regardless of original BMI.

Experts also looked at a small sub-set of people to see how much fat they lost compared with how much (non-fat) lean body mass.

Experts looked at these findings in people aged under 50, 50 to 65 and over 65 years of age.

The team said only a quarter of the weight lost was lean mass, resulting in an overall improvement in body composition.

Across the age groups, the change was almost identical, suggesting there was no evidence of excess lean mass loss in older people, they added.

The authors said: “In this 72-week trial in participants with obesity, tirzepatide once weekly provided substantial reductions in body weight, consistent across all BMI categories, with improvement in body composition that was clinically meaningful and consistent across age groups.”

Dr Louis Aronne, from Weill Cornell Medicine in New York and a consultant to Eli Lilly, who presented the findings, said there was a need to understand the effect of weight loss on fat mass and lean mass, particularly in the elderly.

He added: “This new analysis shows that around three quarters of the weight lost was fat mass, which is consistent across different ages.”

Research published by Eli Lilly in the last month showed tirzepatide helped people with type 2 diabetes who were overweight or obese lose up to 16% of their body weight, or more than 34lb, over nearly 17 months.

A different drug, semaglutide, sold under the brand name Wegovy, has already been approved for use on the NHS for obesity in England.

A decision on whether it will be made available to people in Scotland is expected soon.