Objective: To determine the prevalence and duration of postmenopausal hormone replacement therapy (HRT) use and identify correlates of adherence to therapy.
Design: Population-based cohort study.
Setting: Staff-model health maintenance organization.
Participants: Female members, 40 years and older.
Measurements and main results: Prevalence and duration of use were measured between 1990 and 1995. Duration was assessed by Kaplan-Meier and proportional hazards methods. Hormone replacement therapy use increased from 10.3% in 1990 to 20.7% in 1995. Greatest use (24%) occurred among menopausal women age 50 to 54 years. Less than 5% of women 75 and older used HRT. Among 1,680 first-time recipients of HRT, two thirds of initial prescriptions were written by internists. Thirty-eight percent discontinued HRT within 1 year. For the subset whose indication for therapy was ascertained, prevention of chronic disease was associated with a 33% 1-year discontinuation rate. Factors associated with longer duration of therapy included white race (relative risk [RR], 1.63; 95% confidence interval [95% CI], 1.32 to 2.02), younger age (RR, 1.02 per year; 95% CI 1.01 to 1.03), and changing the preparation or dose of estrogen (RR, 5.62; 95% CI, 4.33 to 7.25). The formulation (esterified estrogens 0.625 mg versus conjugated estrogens 0.625 mg) was also associated with greater duration of use; all other estrogens were, as a group, associated with shorter duration of use. Those who received their initial HRT prescription from an internist were more likely to continue therapy than those who received it from a gynecologist.
Conclusions: Despite increased use of HRT, only a minority of women in this population used HRT, and many of those discontinued therapy within 1 year.