One of my friends had a daughter who went to the Mayo Clinic because many in her family (including her mother) had breast cancer. They identified her as higher risk than others and had her take Tamoxifen as a "preventative."
Everyone responds differently to any medication, but I should never have been put on A.I. drugs because of my severe osteo-arthritis, which put me as one of 3,000 subjects, nationwide accepted into the MOST study, after I had fallen from a bicycle in 1997 and severely injured my left knee. (Couldn't put any weight on it for a year). My mom also had arthritis, as many elderly folks do, and was on medication for that in the nursing home.
My friend said her daughter took it, but it was horrible. I took Tamoxifen for 5 months (and Anastrozole for 7 months) and both were awful, but the Tamoxifen was less horrible.