Bioidentical hormones have the same chemical structure as hormones produced in the human body. There have been many studies demonstrating their safety. At this time, with the ready availability of bioidentical hormones, there is no reason to use non-human formulations. There is a track record of benefit and safety for women taking controlled doses of these hormones, in carefully selected formulations, under medical supervision. Horse hormones and progestins for hormone replacement should become obsolete. Patient demand will make this happen.
As described above, one concern with the use of BHRT is using a custom-mixed solution that has not been FDA-tested. According to the FDA, other concerns can include disguising/leaving untreated symptoms that are really caused by another illness (such as an autoimmune disorder or dietary intolerance) or potential side effects like raising the risk for blood clots, stroke, gallbladder disease, vision changes, skin changes, mood swings, and possibly heart disease or breast cancer. As of now, the FDA has also never approved any drug containing estriol, so keep in mind that benefits associated with products containing this hormone remain especially unknown.