Issues to debate on the Women's Health Initiative (WHI) study. Epidemiology or randomized clinical trials--time out for hormone replacement therapy studies?

Over the last 40 years, there has been increasing epidemiological evidence that post-menopausal treatment with sex steroids in physiological doses may reduce the relative risk of cardiovascular disease (CVD). These findings have been supported by biological studies showing favourable changes in cardiovascular risk factors with estrogen supplementation. The impact of the so-called 'healthy user' bias has been eagerly debated, and the results of the first and only randomized long-term clinical trial of HRT for primary prevention have therefore been long awaited. The dramatic decision to halt the Women's Health Initiative (WHI) study before completion came unexpectedly as the consequence of not only an increased risk of breast cancer but also increased occurrence of cardiovascular events with HRT. Due to the superior design of the study, the results from the WHI study have had an enormous impact on the clinical recommendations of HRT to post-menopausal women, concurrent with a degradation of evidence from observational studies. It is not very likely that other long-term randomized clinical trials (RCTs) will be completed and epidemiology has certainly been disreputed-so is this 'time out' for HRT studies?