Summary: In a prespecified subpopulation analysis of 41 Japanese adults with type 2 diabetes and obesity or overweight enrolled in the SURMOUNT-2 trial, once-weekly tirzepatide produced statistically significant weight loss at week 72: -12.4% with 10 mg (p=0.001) and -10.2% with 15 mg (p=0.013) versus -3.5% with placebo. The very small sample size limits the precision and generalisability of these estimates.
PICO Summary
| Element | Detail |
|---|---|
| Population | 41 Japanese adults with type 2 diabetes and body mass index >=27 kg/m2 (HbA1c 7% to 10%), from 3 trial sites; subpopulation of the multicentre, double-blind, randomised SURMOUNT-2 trial. |
| Intervention | Once-weekly subcutaneous tirzepatide 10 mg or 15 mg as adjunct to lifestyle intervention, over 72 weeks. |
| Comparison | Once-weekly placebo plus lifestyle intervention (n=13). |
| Outcome | Mean percent body-weight change at week 72: tirzepatide 10 mg -12.4% (SE 1.8; p=0.001) and 15 mg -10.2% (SE 1.8; p=0.013) versus placebo -3.5% (SE 1.8). Achieving >=5% weight loss: 85.7% (10 mg) and 78.6% (15 mg) versus 46.2% (placebo). Numerical improvements in glycaemic parameters, waist circumference, systolic blood pressure and lipids were also reported. No 95% confidence intervals, absolute risk reduction or number-needed-to-treat were provided for this subpopulation. No new safety signals were identified. |
Tirzepatide in Japanese adults with T2D and obesity
RCT subpopulation · type 2 diabetes · 72 weeks
Once-weekly tirzepatide produced significant 72-week weight loss versus placebo in Japanese adults with type 2 diabetes and obesity, though the 41-patient sample limits precision.
Expert Commentary
This is a secondary, subpopulation analysis of just 41 Japanese participants drawn from the larger SURMOUNT-2 trial, and it should be read as hypothesis-supporting rather than as independent confirmation of efficacy in this population. The reported weight reductions are large and statistically significant, and the responder rates for at least 5% weight loss were high, which is consistent with the parent trial and with tirzepatide’s established mechanism. The findings are nonetheless constrained by the very small sample, with only around a dozen participants per arm; such numbers inflate the influence of individual responders, widen the true uncertainty around each estimate, and make the absence of reported confidence intervals a meaningful gap. It is also notable that the 15 mg dose produced numerically less weight loss than 10 mg, which argues against a clean dose-response signal and is most plausibly a chance finding at this sample size. The trial was sponsored by the manufacturer, Eli Lilly, and two authors are company employees, so the framing of results warrants the usual caution. Can I use this with my patients? For Japanese adults with type 2 diabetes and obesity already considered for tirzepatide, this analysis is reassuring but not practice-changing on its own. Larger Japan-specific data should anchor firm dosing decisions.
References
Yamauchi T, Asakura T, Shingaki T, Oura T, Katagiri H. Efficacy and safety of once-weekly tirzepatide in Japanese participants with type 2 diabetes who have obesity or overweight: Subpopulation analysis of the SURMOUNT-2 trial. Diabetes Obes Metab. 2025;27(8):4557-4566. doi:10.1111/dom.16500