The evidence base for HRT: what can we believe?

Prior to the unexpected early termination of the Women's Health Initiative (WHI) trial of continuous conjugated equine estrogens (CEE) and medroxyprogesterone acetate (MPA), the prevailing view was that hormone replacement therapy (HRT) was a low-risk intervention with immediate value for symptom relief in recently menopausal women, and that it probably conferred long-term protection against the major chronic diseases that affect women after menopause. Rather than replicating prior studies, the WHI was designed to test whether the beneficial associations consistently seen in women starting HRT near menopause would be found in women well beyond menopause. Views of the benefits and risks of HRT changed dramatically in 2002 with the unexpected early termination of the CEE + MPA trial and the alarming initial WHI report. HRT use plummeted world-wide, driven by fear of breast cancer and skepticism about cardiovascular benefits. Stunningly, the contrasting findings of the WHI trial of CEE alone reported 2 years later - suggesting prevention of coronary heart disease in women who began HRT at age <60 years, and a reduction in breast cancer overall - were largely ignored. Key lessons from the WHI are that the effects of HRT on most organ systems vary by age and time since last physiologic exposure to hormones and that there are differences between regimens. In the years since the first WHI report, we have learned much about the characteristics of women who are likely to benefit from HRT. The range of HRT regimens has also increased. Not all women have indications for HRT, but for those who do and who initiate within 10 years of menopause, benefits are both short-term (vasomotor, dyspareunia), and long-term (bone health, coronary risk reduction). Critically, the 'facts' that most women and clinicians consider in making the decision to use, or not use, HRT are frequently wrong or incorrectly applied.