New analysis finds semaglutide and tirzepatide produce similar weight loss in type 2 diabetes

Researchers have found that semaglutide and tirzepatide, two of the most widely prescribed GLP-1 medicines, produce statistically similar weight loss in people with type 2 diabetes when specific doses are compared, according to an analysis published in the journal Diabetes Therapy ^[1][2]. The study pooled data from 23 phase III trials involving more than 16,500 people with type 2 diabetes, drawing on the SUSTAIN, STEP, SURPASS and SURMOUNT trial programs ^[1][2].

The research team, led by Carlos E. Builes-Montaño of Hospital Pablo Tobón Uribe and the University of Antioquia, along with Novo Nordisk colleagues, analyzed 48 treatment arms and 16,524 participants ^[1][2]. Fifteen trials covered semaglutide doses from 0.5 to 7.2 milligrams weekly, and eight trials covered tirzepatide at 5, 10 and 15 milligrams weekly, with treatment lasting 26 to 104 weeks ^[1][2]. Using statistical models that map dose to weight change, the team found that semaglutide at 2.4 milligrams and tirzepatide at 10 milligrams had a 99.4 percent probability of producing equivalent weight loss, defined as a difference of no more than 2 percentage points ^[1][2]. Semaglutide at 7.2 milligrams and tirzepatide at 15 milligrams showed a 94.8 percent probability of equivalence ^[1][2]. Lower-dose semaglutide, at 1.0 milligram, did not match higher-dose tirzepatide, with near-zero equivalence probabilities ^[1][2].

The analysis also modeled what happens when patients switch drugs or increase dose. For people on semaglutide 1.0 milligram, escalating within the same drug to 2.4 milligrams carried a higher chance of extra weight loss than switching to tirzepatide 5 milligrams ^[1][2]. But for people already on tirzepatide 10 milligrams, switching to semaglutide 7.2 milligrams showed a larger expected benefit than moving up to tirzepatide 15 milligrams ^[1][2]. The authors describe the results as dose-driven rather than drug-driven, meaning it is the amount of medicine, not which molecule, that appears to determine weight-loss outcomes at these matched levels ^[1][2].

The study has real limits. It relied on combined trial-arm data rather than individual patient records, so it could not adjust for factors like other medications or health conditions ^[1][2]. The estimate for semaglutide's highest dose, 7.2 milligrams, rests on a single trial and is described as exploratory ^[1][2]. The analysis also did not examine blood sugar control, heart-related outcomes, or safety and side effects, focusing only on weight ^[1][2]. Only one head-to-head trial, SURMOUNT-5, has directly compared the two drugs, and it was conducted in people with obesity but not diabetes, comparing maximum doses rather than the full range studied here ^[1][2].

Why it matters for patients

For people with type 2 diabetes, this analysis suggests that switching between semaglutide (Ozempic, Wegovy, Rybelsus) and tirzepatide (Mounjaro, Zepbound) at matched doses may not mean a large difference in expected weight loss, which could matter when insurance coverage, drug shortages, or cost push a switch ^[1][2]. This differs from obesity trials without diabetes, where tirzepatide has generally shown an edge in weight loss over semaglutide, a gap this new analysis does not address or overturn ^[1][2]. The findings do not cover people without diabetes, and they say nothing about side effects, blood sugar control, or heart outcomes, all of which remain part of any treatment decision ^[1][2]. Whether these dose-equivalence patterns hold in real-world use, outside of clinical trials, is not yet known.

What happens next

The authors note their approach could serve as a template for comparing drugs when head-to-head trials are not available, and they call for more direct trials to confirm the dose-equivalence patterns, particularly at semaglutide's highest dose, which is based on only one trial so far ^[1][2]. No date has been given for additional confirmatory research.