Tamoxifen has proved to be effective in prolonging life in women who have been treated for breast cancer. It also reduces the chances of getting cancer in the opposite breast. It is recommended that tamoxifen treatment be continued for 5 years. In about 1 in every 100 patients, treatment with tamoxifen may cause blood clots in the veins. Rarely, these can pass into the lung, endangering life.
Tamoxifen has some beneficial side effects, too.