Hormone therapy: physiological complexity belies therapeutic simplicity

The results of the Women's Health Initiative, a study anticipated to provide definitive answers about health benefits and risks of postmenopausal hormone therapy, have generated debate and confusion among clinicians, researchers, and the lay public. The ovarian hormones estrogen and progesterone, which decline at menopause, normally elicit complex tissue-specific responses throughout the body. Major advances are providing a detailed molecular definition of how that differential action is achieved. Here we review estrogen and progestin actions, discuss how effectively knowledge of steroid hormone endocrinology has been incorporated into clinical studies, and consider the impact on modern hormone therapy protocols and pharmaceutical development.