It can depend on your age and menopause status. If you are younger then it's possible to get a period back on Tamoxifen.If you are older and over menopause then any spotting needs checking whilst on Tamoxifen.Mind you,it's not uncommon to have spotting whenever you start or stop Tamoxifen.If not menopausal then you will have oestrogen circulating.Tamoxifen blocks oestrogen from entering any breast cancer cells which need this hormone to grow.So I would think it's doing it's job but I am no expert so maybe you need more indepth explanation from your specialist.Try not to worry because Tamoxifen is very effective against our type of breast cancer. Tonya xx