Body identical hormone replacement.

The adverse outcomes seen in the Women's Health Initiative (WHI) 1 were mainly due to an over-dosage of hormones in a relatively elderly population. However, fundamental differences exist between conjugated equine estrogens and 17 beta estradiol and between medroxyprogesterone acetate and natural progesterone. It is likely that these differences also contributed to the adverse outcomes in WHI, which were contrary to the cardiovascular benefits seen in previous observational trials. Recent studies of cardiovascular risk markers in younger women have been designed using predominantly estradiol and natural progesterone (transdermal and oral) as the primary interventions. This paper reviews the effects that body identical estradiol and progesterone can have, both in the physiological environment and also when replaced as transdermal estradiol and micronised oral progesterone.