Were women studied in the tirzepatide obesity trials?

Tirzepatide is a dual GIP and GLP-1 receptor agonist approved for chronic weight management as Zepbound and for type 2 diabetes as Mounjaro. Because weight-management medicines are used by large numbers of women, the representation and analysis of women in the pivotal obesity trials matters.

The flagship obesity trial, SURMOUNT-1, randomized 2,539 adults with obesity or overweight without diabetes to tirzepatide 5 mg, 10 mg, 15 mg, or placebo. The trial was published in the New England Journal of Medicine in 2022. According to the published baseline characteristics and the FDA statistical review, the mean age was about 45 years and roughly 67.5% of participants were female. That is strong numerical representation.

But representation is not the same as analysis. The FDA statistical review for the Zepbound New Drug Application reported a significant treatment-by-sex interaction in SURMOUNT-1. The review described the interaction as quantitative, meaning tirzepatide produced greater weight loss than placebo in both females and males, but the magnitude appeared larger in females. The review also noted that the finding would need further investigation.

A separate industry-reported subgroup analysis of the SURMOUNT program, presented at the 2024 European Association for the Study of Diabetes meeting, similarly described greater body-weight reduction with tirzepatide in females compared with males across the pooled trials. These analyses are informative, but they share a common limitation: the trials were designed and powered for overall efficacy, not for sex comparisons.

Other details that would help women interpret the evidence are missing or sparse. Menopausal status is not routinely reported. Contraceptive use is not described. Pregnancy and lactation were exclusion criteria, so the trials provide no direct evidence for those life stages. The label reflects that gap, recommending that tirzepatide be stopped as soon as pregnancy is recognized and noting limited lactation data.

So were women studied? Yes, in large numbers. Do we have fully sex-specific, life-stage-specific conclusions? Not yet. The evidence supports overall efficacy and safety in the enrolled population, but women-and their clinicians-should treat the available sex subgroup findings as suggestive rather than definitive.