The Women's Health Initiative Study (WHI) was sponsored by the US National Institutes of Health to evaluate the effects of hormone replacement therapy (HRT). Results of the study have now been reviewed in many countries, and some highlights are proposed in the following summaries.

The study has several ongoing components, one of which was designed to assess the effects of conjugated equine estrogens and medroxyprogesterone acetate on the risk of developing heart disease. This arm was halted early in July 2002 when the independent data monitoring committee detected an excess risk in the estrogen/progestogen group: patients had a 26% increase in the relative risk of invasive breast cancer, a 41% increase in the risk of stroke and a 22% increase in heart disease compared to women taking placebo.

These results do not necessarily apply to lower doses of HRT or to other combination HRT products. Although there was an increase in vascular events, many of the women in the study had pre-existing risk factors for cardiovascular disease. However, since no long-term trials of combined hormone replacement therapy are continuing, the balance between benefit and harm will remain uncertain. It seems that hormone replacement therapy may continue to be prescribed for menopausal symptoms and osteoporosis prevention, but the need for continued use should be reviewed annually.