They are commonly used in birth control pills and mistakenly given to postmenopausal women in place of natural progesterone. The progesterone revolution refers to the change in medical and societal thinking regarding hormone balancing, hormone replacement therapy, and recognition of the dangers of unopposed estrogen. This revolution follows from several factors operating independently and together such that a new understanding and a new therapeutic protocol has emerged. The major factors in this revolution are the following. In 1976 it became apparent that estrogen supplementation increases the risk of endometrial cancer six-fold or more.
Several researchers consider unopposed estrogen to be the only known cause of endometrial cancer.
All researchers agree that estrogen should never be supplemented without progesterone or one of the synthetic progestins to protect against this cancer risk. As might be imagined, the pharmaceutical industry took this opportunity to advertise their various progestins to doctors. The New England Journal of Medicine editorialized that it was too bad that natural progesterone was not available to women. By 1989, reports indicated that estrogen supplements increased the risk of breast cancer, and the addition of synthetic progestins increased it even more. Fractures may be delayed but not prevented.