Use of tirzepatide is associated with significantly greater weight loss than semaglutide, according to the results of the first head-to-head study.
An analysis of electronic health data from more than 18,000 patients taking one or the other found those on tirzepatide also had greater differences in weight loss at both three months and 12 months.
Researchers initially considered health records from more than 41,000 patients before identifying a cohort that could be matched for comparison.
At three months the average reduction in body weight was 5.8% for tirzepatide compared with 3.6% for semaglutide. By six months this was 10.1% versus 5.8% and 15.3% with tirzepatide compared with 8.3% for semaglutide after a year.
Adjusting for confounding factors, the researchers said there was a 7% difference in weight loss between the two drugs in those who were still on treatment after a year.
Findings were replicated in sub-groups of patients with or without type 2 diabetes, the study published in JAMA Internal Medicine found.
But as has been noted in other clinical trials for both drugs, larger weight loss was found in patients without type 2 diabetes compared with patients with the condition. The underlying reason for this is not yet clear, the team reported.
There were no significant differences in the incidence of gastrointestinal side effects, the researchers added.
Yet they also stressed that most patients in the study did not stick with the treatment. Follow up was halted in 55.9% of those on tirzepatide and 52.5% on semaglutide.
More research is also needed to compare the two drugs on other outcomes such as the reduction of major cardiovascular events, they concluded.
‘To our knowledge, this study represents the first clinical comparative effectiveness study of tirzepatide and semaglutide in adults with overweight or obesity,’ they concluded.
‘In this population of adults with overweight or obesity, use of tirzepatide was associated with significantly greater weight loss than semaglutide.’
Last week researchers reported “significant but tentative” findings that patients taking semaglutide were four times more likely to be diagnosed with an eye condition known as non-arteritic anterior ischemic optic neuropathy (naion).
Writing in JAMA Ophthalmology about more than 16,000 patients who had been treated for the condition over a six-year period, clinicians found a higher risk among those on the drug for both diabetes and overweight compared with those who had the conditions but were not taking it.
Under draft NICE recommendations currently out for consultation, GPs will be able to prescribe tirzepatide for weight loss, marking a shift from guidance on semaglutide for weight loss that said it should only be available through specialist provision.
In another departure from guidelines on semaglutide treatment, which is limited to two years, the committee did not give advice on how long tirzepatide should be given for.
Experts said the recommendations could widen access as well as driving down cost.
