Summary: In adults with overweight or obesity and type 2 diabetes, an indirect treatment comparison anchored on the SURMOUNT-2 and STEP 2 placebo arms reported that tirzepatide 10 mg and 15 mg once weekly were associated with statistically significant greater reductions in body weight, BMI and HbA1c than semaglutide 2.4 mg once weekly. Estimated treatment differences in body weight were about 2.6 percent for the 10 mg dose and 4.8 percent for the 15 mg dose, with safety broadly comparable. No head-to-head trial was performed.
PICO Summary
| Element | Detail |
|---|---|
| Population | Adults with type 2 diabetes and BMI at least 27 kg/m2, HbA1c 7 to 10 percent on stable therapy, with at least one prior unsuccessful dietary weight-loss attempt. Data drawn indirectly from two multinational phase 3 randomised trials, SURMOUNT-2 and STEP 2. |
| Intervention | Tirzepatide 10 mg and 15 mg subcutaneously once weekly (efficacy estimated indirectly from the SURMOUNT-2 trial arms), adjunct to reduced-calorie diet and physical activity. |
| Comparison | Semaglutide 2.4 mg subcutaneously once weekly (efficacy estimated indirectly from the STEP 2 trial arm). Comparison made through a Bucher indirect treatment comparison using placebo as the common anchor; the two agents were never compared directly. |
| Outcome | Estimated treatment differences in percent body weight change versus semaglutide 2.4 mg: tirzepatide 10 mg about -2.57 percent (95% CI -4.26 to -0.87) and tirzepatide 15 mg about -4.79 percent (95% CI -6.51 to -3.07). HbA1c difference for tirzepatide 10 mg about -0.47 percentage points (95% CI -0.70 to -0.24), with a larger point estimate for 15 mg. Tirzepatide 15 mg showed significantly greater odds of at least 5 percent and at least 15 percent weight loss and significant improvements in waist circumference, fasting plasma glucose and triglycerides. Lipid and blood-pressure differences were non-significant trends. Safety was broadly comparable. As an indirect comparison, these are associational estimates, not direct head-to-head proof. |
Tirzepatide vs semaglutide 2.4 mg in T2D obesity
Bucher indirect comparison · SURMOUNT-2 vs STEP 2
In this manufacturer-funded indirect comparison, tirzepatide 10 mg and 15 mg were associated with greater weight, BMI and HbA1c reduction than semaglutide 2.4 mg. As a Bucher indirect comparison it cannot prove head-to-head superiority.
Expert Commentary
This analysis is an indirect treatment comparison, not a head-to-head trial, and that distinction governs how much weight its conclusions can carry. Using the placebo arms of SURMOUNT-2 and STEP 2 as a common anchor through a Bucher comparison, the authors report that tirzepatide 10 mg and 15 mg were associated with greater reductions in weight, BMI and HbA1c than semaglutide 2.4 mg, with the 15 mg dose also improving several cardiometabolic measures. The estimated body-weight advantage, roughly 2.6 to 4.8 percent depending on dose, is directionally consistent with what later direct comparisons have suggested, which lends the signal some credibility. The decisive limitation is the method itself: indirect comparisons assume the source trials are exchangeable in design and population, and any residual difference between SURMOUNT-2 and STEP 2 is silently absorbed into the estimate, so the confidence intervals understate the true uncertainty. The analysis was funded and largely authored by the manufacturer of tirzepatide, which warrants cautious interpretation of an already favourable result. Can I use this with my patients? Cautiously, yes, as supportive context when counselling a patient with type 2 diabetes and obesity who is weighing the two agents, but not as definitive proof of superiority. Clinicians should anchor decisions on direct randomised evidence as it matures and on individual tolerability, cost and access.
References
Ciudin A, Johansson E, Zimner-Rapuch S, Dimitriadis GK, Bertrand M, Curteis T, et al. Indirect comparative efficacy and safety of tirzepatide 10 and 15 mg versus semaglutide 2.4 mg for the management of obesity and overweight in patients with type 2 diabetes. Diabetes Obes Metab. 2025;27(9):4709-4719. doi:10.1111/dom.16508