Blockbuster weight loss jab Mounjaro is almost 50 per cent more effective at shifting the pounds than its rival Wegovy, the first head-to-head trial of the medications has revealed.

The ingredient tirzepatide, available as Mounjaro, has long been hailed the ‘King Kong’ of slimming jabs and a breakthrough in the war on obesity.

Now, US researchers have found those on the injections typically lost a fifth of their body weight in just over a year. 

By comparison, semaglutide users—sold as Wegovy—lost around 13.7 per cent on average over the same 72-week period. 

Both jabs are the only two currently available on the NHS for weight loss, but users must meet strict health criteria. 

Scientists today said both drugs had a role to play in combatting the obesity crisis, but Mounjaro sales would now likely surge. 

Dr Louis Aronne, an expert in metabolic health at Cornell University in New York and study co-author, said: ‘The majority of people with obesity will do just fine with semaglutide—Wegovy.

‘Those at the higher end may ultimately do better with tirzepatide—Mounjaro.’

The ingredient tirzepatide, available as Mounjaro, has been hailed the ‘King Kong’ of slimming jabs and a breakthrough in the war on obesity

US researchers found those on Mounjaro typically lost a fifth of their body weight in just over a year. By comparison, semaglutide users—sold as Wegovy—lost around 13.7 per cent on average over the same 72-week period 

Professor Naveed Sattar, an expert in cardiometabolic medicine at the University of Glasgow, who wasn’t involved in the research, added that the drugs were ‘good options’ for patients.

While some ‘will be satisfied with 15 per cent weight loss, many want as much weight loss as possible’, he added.

‘In the UK, tirzepatide sales privately are now well ahead of semaglutide—that’s just a reality—and this paper will accelerate that I imagine.’

Administered weekly, both injections are designed to help type 2 diabetes patients control their blood sugar levels or for obese people to lose weight for health purposes. 

Wegovy mimics a hormone released by the body after a meal to flip one appetite switch in the brain. Mounjaro, or tirzepatide, flips two.

However, the jabs are also known to cause worrying side effects such as pancreatitis — when the pancreas suddenly becomes inflamed — or gastrointestinal issues.

The trial, funded by Mounjaro manufacturer Eli Lilly, involved 750 obese people, with an average weight of 113kg (nearly 18 stone).

They were asked to take the highest dose they could tolerate of one of the two drugs.

This map highlights the areas most blighted by obesity

Presenting the findings at the European Congress on Obesity in Malaga and in the New England Journal of Medicine, researchers said 32 per cent of slimmers lost a quarter of their body weight on Mounjaro.

By comparison, around 16 per cent of people on Wegovy saw the same weight loss. 

Those on Mounjaro lost an average of 18cm from their waistlines compared with 13cm on Wegovy.

Mounjaro users also had better blood pressure, blood sugar and cholesterol levels, while both groups suffered similar levels of side effects. 

At least half a million NHS patients and some 15million in the US are now thought to be using weight loss jabs, which can help patients lose up to 20 per cent of their bodyweight in just a few months.

They have also been shown to significantly reduce the risk of heart attacks and strokes.

However, other reported problems using the jabs include constipation, fatigue, headaches, dizziness and even hair loss. 

Under official guidelines, only patients who have a body mass index (BMI) of over 35 and at least one weight-related health problem like high blood pressure, or those who have a BMI of 30 to 34.9 and meet the criteria for referral to a specialist weight management service, should be prescribed weight loss jabs.

Obesity itself increases the chances of person suffering serious health conditions that can damage the heart, such as high blood pressure, as well as cancers.

Around two in three adults in the UK are obese or overweight, giving the country one of the highest obesity rates in Europe.

Last year, a sobering report also suggested Britain’s spiraling obesity levels have fuelled a staggering 39 per cent rise in type 2 diabetes among people under 40, with 168,000 Brits now living with the illness.

Piling on the pounds has also been linked to at least 13 types of cancer and is the second biggest cause of the disease in the UK, according to Cancer Research UK.