With the rise in obesity, there has been a concomitant increase in prescription medications associated with weight gain. The objective of this study is to quantify the magnitude of association between putative weight-promoting medications and 3-year weight change in a diverse cohort of postmenopausal women in the Women's Health Initiative (WHI). This is a prospective observational cohort study, considering 40 sites in the WHI and a cohort of seventy six thousand two hundred fifty-two postmenopausal women aged 50-79 years, with weight measured at both baseline and 3 years, in the WHI-Observational Study. Body mass index (BMI) and waist circumference (WC) were measured at baseline and 3 years. An in-clinic medication inventory identified prescribed medications, including antidepressants, beta-blockers, insulin, and/or glucocorticosteroids. Generalized linear models evaluated if intermittent or persistent use of weight-promoting drugs was associated with increased BMI and WC during a 3-year follow up. Women with overweight or obesity at baseline were more likely to be taking antidepressants, beta-blockers, and/or insulin. Taking at least one putative weight-promoting medication was associated with a greater increase in BMI (0.37 vs 0.27 kg/m, P = 0.0045) and WC (1.10 cm vs 0.89 cm, P = 0.0077) over the course of 3 years compared to women not on these medications. Both BMI and WC increased with the number of weight-promoting drugs prescribed (P for trend per medication used < 0.00001 for both variables). Those who took either antidepressants or insulin, or a combination of antidepressants and beta-blockers, were most likely to have a significant increase in BMI compared to nonusers. Antidepressants, beta-blockers, and insulin were associated with weight gain in postmenopausal women. This information may help to inform clinical decision-making and efforts to mitigate medication-related weight gain. : Video Summary:http://links.lww.com/MENO/A617.