People who use the drug Mounjaro are able to sustain weight loss for three years, data from a trial suggests.
Mounjaro, nicknamed the “King Kong” of weight loss drugs, contains tirzepatide and is self-administered in once-a-week injections.
It works by mimicking two hormones called GLP-1 and GIP, resulting in appetite suppression, increased production of insulin, greater insulin sensitivity and a reduction in the rate at which food is emptied from the stomach. The medication is available for weight loss to some people on the NHS and it can also be bought privately with a prescription.
Scientists at Eli Lilly, the company that makes Mounjaro, along with academic researchers have released two analyses of data from a three-year trial known as Surmount-1, throwing fresh light on the medication’s longer-term use. One analysis looked at trajectories of weight loss, the second at rebound after initial weight reduction.
The results, which are to be presented at the European Congress on Obesity in Málaga next month and have yet to be peer reviewed, are based on data from about 700 participants who took tirzepatide in three different dose regimens during the 176-week study. All had obesity or were overweight and had pre-diabetes.
The results reveal participants’ experiences tended to follow one of three patterns – either steady, medium or rapid weight loss, followed by a plateau, which occurred later the faster the initial drop. The team said the final average body weight reductions for these groups were 9.2%, 20.2% and 30.8% respectively. Each group encompassed around a third of the participants.
“[The work] demonstrates that we can in some way predict total final weight loss from the speed of weight loss observed in the first months of treatment,” said Prof Luca Busetto, of the University of Padova in Italy, one of the scientists behind the first analysis.
The researchers said most of the participants maintained clinically meaningful weight reduction over the course of the study. This was supported by a second analysis that found that average time to the lowest weight reached was 22 months, at which point participants had lost 23.1% of their starting weight on average.
While some subsequently regained weight – despite continuing with the medication – participants had nonetheless lost 19.4% of their starting weight, on average, by the end of the study.
The team added that 70% of participants regained less than 5% of their starting weight after hitting their lowest point.
Prof Naveed Sattar, of the University of Glasgow, who was not involved in the trial, said the finding of different weight loss trajectories could help give an indication of how much weight an individual might expect to lose in the long term. “That might be able to guide the need for some individuals to consider newer therapies, which are more potent, in the future,” he said.
Dr Simon Cork, of Anglia Ruskin University, said the other analysis demonstrated the long-term effectiveness of tirzepatide in maintaining weight loss, which would be of interest to health bodies “as the costs of treating obesity-related co-morbidities rise year on year”.
Cork also noted long-term effectiveness and safety studies for such drugs were now at odds with guidance, which limits their use to a maximum of two years.
The findings come as the Advertising Standards Authority announced that along with the Medicines and Healthcare products Regulatory Agency and the General Pharmaceutical Council, it had warned businesses that advertising prescription-only medications to the public was prohibited. This includes weight loss jabs such as Mounjaro, Wegovy and Saxenda.
Among other examples, the rules cover paid-for ads on social media “such as image or video ads on Facebook, Instagram and TikTok”, sponsored searches on Google or other search engines, and ads by influencers.
A Guardian investigation previously revealed that weight-loss injections were being aggressively marketed to British consumers through often illegal promotions.