When women with early stage breast cancer take tamoxifen after surgery, they generally take it for 5 years. Studies have shown that taking it for more than 5 years does not increase the benefit of the drug. The long-term effects of taking tamoxifen are still not known. Women with advanced disease take the drug for different lengths of time, depending on many factors. One factor is the effectiveness of the other treatments used.
Some women report some side effects.
Many do not. Tamoxifen's side effects are similar to the symptoms of menopause. But tamoxifen does not cause menopause. However, women who are close to menopause may enter it early because of the drug. Women also report other side effects which are less common.