‘King Kong’ weight-loss jab Mounjaro set to lose its crown as new ‘Godzilla’ injection retatrutide outperforms it, major review finds

Mounjaro is the most powerful weight-loss jab currently available – but it may soon be toppled by ‘Godzilla’ drug retatrutide and other emerging injections, a study suggests.

Researchers found tirzepatide – the active ingredient in the blockbuster drug dubbed the ‘King Kong’ of weight-loss jabs – can see patients shed more than a fifth of their body weight after around 17 months.

But retatrutide, nicknamed ‘Godzilla’ because it is hoped to be even more powerful, can see patients lose almost a quarter of their weight after just 48 weeks.

Known as ‘Reta’, the experimental jab has yet to be approved for widespread use, although it was given the green light in the US last month for select patients with an urgent need.

Another experimental jab, amycretin, produced almost the exact same level of weight loss as retatrutide after just 36 weeks.

This suggests the drugs could become the most potent weight-loss jabs ever developed if they get the green light from health officials.

By comparison, semaglutide injections such as Wegovy and Ozempic can trigger weight loss of up to 18.7 per cent over a similar period.

Mounjaro also appears to produce greater weight loss than the new once-daily tablet treatments recently approved in the UK – the Wegovy pill and Foundayo.

The Wegovy pill can see patients lose as much as 15.5 per cent of their body weight after 68 weeks, the study showed.

Meanwhile Foundayo, also known as orforglipron, can see patients lose up to 14.7 per cent – though this is after just 36 weeks.

Researchers launched a new so-called systematic review of the drugs, known as GLP-1s, after carrying out a similar analysis last year.

They analysed 38 trials with more than 25,000 participants to study the safety and efficacy of the treatments compared with placebo medicines.

This included looking at new, experimental drugs which are yet to be approved, including retatrutide and amycretin.

The increasing potency of the drugs is thought to be partly down to the number of different hormones they mimic in the body.

Semaglutide, the drug behind Wegovy and Ozempic, mimics a gut hormone called GLP-1, which helps people feel fuller for longer and reduces appetite.

Tirzepatide – the drug in Mounjaro – went one step further by mimicking both GLP-1 and another hormone called GIP, which is also involved in regulating appetite and blood sugar. 

Experts believe targeting the two pathways together is one reason it can produce greater weight loss than semaglutide.

Retatrutide goes further still. Known as a ‘triple agonist’, it targets GLP-1 and GIP as well as a third hormone, glucagon.

As well as helping control appetite, glucagon is thought to increase the amount of energy the body burns – potentially explaining why retatrutide has produced even greater weight loss in trials.

Amycretin works differently again. It targets GLP-1 alongside amylin, a hormone released by the pancreas after eating which sends signals to the brain that help people feel full.

The researchers, from McGill University and the Jewish General Hospital in Montreal, Canada, also looked at side effects reported by people using the drugs.

Around 40 per cent of people on placebos in the trials reported gastrointestinal side effects, compared with 76 per cent of those who took the jabs or pills.

These have long been known as the most common side effects of the drugs and include diarrhoea, vomiting, nausea and constipation.

Around 10 per cent of people had to stop taking the drugs as a result.

There were also rare reports of severe biliary disorders, which typically include gallstones, as well as pancreatitis, psychiatric disorders and six deaths.

The researchers, whose findings were published in the Annals of Internal Medicine journal, noted that the trials for each of the drugs differed, meaning the results cannot be directly compared.

The findings relating to the drugs’ side effects also come after official drug safety figures separately showed 216 deaths in the UK have been linked to the jabs.

Earlier this month, the Daily Mail reported that a total of 150,000 adverse reactions have also been associated with the drugs.

Semaglutide was linked to 59 deaths, meanwhile, liraglutide, known as Saxenda, was associated with 37 fatalities.

The figures were uncovered in so-called Yellow Card reports made to the Medicines and Healthcare products Regulatory Agency.

Officials said that the reports do not prove that a medicine caused a reaction to happen, only that it is suspected by the individual making the report. Other health conditions may have been at play.