I had 4 different drugs over a 4.5 year period post mastectomy. The side effects of each of them were horrible, and each time they became unbearable, I was changed onto a different one.... and then experienced different side effects. I took Tamoxifen, then Arimidex, then Toremefine, then back onto Tamoxifen again.
Eventually after 4.5 years my consultant said they had done their job and I could stop them. It took about 2 years to get the side effects out of my system, but I was also coping with other illnesses, so it was hard to tell what was causing what.