Background: In July 2002, the Women's Health Initiative (WHI) published results that led to early termination of the randomized controlled trial of estrogen plus progestin in postmenopausal women with an intact uterus. Subsequently, the trial of estrogen only also was terminated early, and the results were published in April 2004. The present study examines the impact of both sets of results on menopausal hormone therapy (MHT) prescription patterns, as well as the characteristics of women who did and did not change their MHT behavior after publication of results.
Methods: We examined the number of MHT prescriptions filled in the months before and after each set of results was published, using claims data from 24,446 women aged 50-79 years continuously enrolled in a health maintenance organization (HMO) at Henry Ford Health System from January 2000 through December 2004.
Results: After July 2002, a statistically significant (p < 0.05) drop occurred in the rate of MHT prescriptions filled; 29% of the women stopped MHT for at least 4 months, but 24% of these women resumed use by December 2004. Successful stoppers tended to be older. Twenty-one percent of users in April 2004 stopped in May 2004 for at least 4 months; 25% of these had restarted by December. Women continued to initiate MHT after July 2002, but at lower rates in 2003 and 2004 (73% and 77% decreases, respectively, compared with 2001). The types of MHT prescriptions obtained by new users changed after 2001: fewer initiated MHT with oral Premarin (Wyeth, St. David's, PA) and Prempro or Premphase (Wyeth-Ayerst, Philadelphia, PA), and more initiated MHT with Premarin and Estrace (Warner Chilcott, Rockaway, NJ) creams.
Conclusions: Regardless of the goals of the WHI study, the publication of results on estrogen plus progestin in July 2002 impacted overall rates of MHT use, as did, to a lesser extent, the estrogen only results published in May 2004. Although women continued to initiate MHT after the results were published, they were less likely to use the formulations from the WHI and instead used formulations for which there is less information about effectiveness and long-term health consequences.