Objective: We sought to examine prescribing patterns (prevalence and rates of initiation and discontinuation) for estrogen plus progestin (hormone therapy [HT] and estrogen alone [ET]) in the United States in the 2 years before the published results of Women's Health Initiative's (WHI) HT trial's early termination and for 5 months after their release.
Methods: We conducted an observational cohort study of 169,586 women aged 40-80 years who were enrolled in 5 health maintenance organizations in the United States to estimate the prevalence of HT and ET and discontinuation and initiation rates between September 1, 1999, to June 31, 2002 (baseline), and December 31, 2002 (follow-up). We used automated pharmacy data to identify all oral and transdermal estrogen and progestin dispensed during the study period.
Results: The prevalence of HT declined 46% from baseline to follow-up (14.6% to 7.9%); ET use declined 28% during the same period (12.6% to 9.1%). The discontinuation of HT increased almost immediately, from 2.5% at baseline to 13.8% in October 2002. We saw an immediate decrease in HT and ET initiation rates, from 0.4% and 0.3% at baseline, respectively, to 0.2% for HT and ET at follow-up.
Conclusion: The diffusion of the WHI HT trial results had an immediate impact on the discontinuation of HT and ET and is likely responsible for the 46% and 28% decline in the initiation of these respective therapies. Further exploration of why women continue to use HT and identification of methods for addressing reasons for continued use are indicated.
Level of evidence: II-2.