Progestins, synthetic progesterone analogs, joined estrogen as part of hormone replacement therapy (HRT) some two decades ago, to reduce perceived risks of endometrial cancer from estrogen alone. But for almost as long, researchers have suspected that progestins block some benign effects of estrogen replacement, increasing the risk of breast cancer, diminishing estrogen's beneficial effects on the cardiovascular system, and souring mood. So, researchers continue to study progestins in search of safer HRT.
Jon Nilsen and Roberta Brinton, University of Southern California, recently showed how natural estrogen and progesterone protect hippocampal neurons from glutamate toxicity. But at least one progestin, medroxyprogesterone acetate (MPA), blocks that protection.1 MPA is the progestin component of Prempro, the HRT used in the Women's Health Initiative (WHI) clinical trials. The US government shut down that arm of the WHI study in July 2002--three years early--after discovering small increases in breast cancer, heart disease, stroke, and pulmonary ...
