I spent a few years on an estrogen blocker and my primary side effects were joint aches, difficulty with concentration, and temporary hot flashes. When the estrogen blocker was eventually discontinued, the joint pain and foggy thinking remained. I have experienced significant improvement on compounded bi-Est even though the dosage is very low. My physician can choose a dosage that is geared and adjusted specifically for my needs with the lowest effective amount. He can make minute adjustments with unlimited choices, as far as I understand, so that the medication is custom made for me and my symptoms, if they change over time.