I have been on anastrozole for 6 months and my most disturbing side effect is overwhelming fatigue. I was never this exhausted throughout chemo or radiation so my oncologist doesn't believe it is related to any of the cancer treatment (bilateral mastectomy, chemo, rads, anastrozole). It slammed me three days after starting the anastrozole and I can't overcome it despite PT, OT, Acupuncture, Psychotherapy, and naturopathic medicine. Oncologist refuses to believe it has anything to do with anastrozole therefore is unwilling to try something else.