A good question--and maybe ask oncologist too. I've been on letrozole for almost four years without any side effects. No depression or mood swings. But many women do have side effects. Do you have any routines or other things that can help with the depression that aren't medication? I will add that since the cancer diagnosis I exercise every day, am in psychotherapy, and keep a journal. These things might have helped my mood. A friend of mine is in a breast cancer support group which has really helped here. I've needed support, and sought it out.