No I don't think the tamoxifen had anything to do with my new tumour. I think it was due to my high eostrogen levels. Then again, I've had radiation and tons of mammograms on that breast, so who knows if they had any effect? I didn't have much trouble on the Tamoxifen, although I did gain weight during the time I was on it. I used to blame the weight gain on the Tamoxifen, but I've lost and gained weight in the 5 years I've been off it, so I guess I'm just eating too much!! I still had regular periods while I took it. In 2009 and 2011, I had polyps form in my uterus (one on each occasion). They were removed and were benign, but I was told they could have been caused by the Tamoxifen. Overall, I found it to be ok. I think the Femara has more side effects, but they aren't too bad either, especially compared to having chemo!! Everything seems cruisy compared to that! When I first had chemo in 2002, it was horrendous; lots of vomiting and ulceration etc. When I had it again in 2011, it was a breeze by comparison. The drugs and anti-nausea stuff had improved tremendously. Good luck and lots of love x Jane