Tamoxifen is a form of estrogen. It is used to treat breast cancer in both sexes and to lower the risk of developing breast cancer if a woman is at high risk.

If you are taking tamoxifen for preventive reasons, you may need to take the first dose while on a menstrual period. Follow your doctor’s instructions carefully. Take with or without food. If you require surgery, medical tests, or bed rest, you may need to temporarily stop using tamoxifen, so inform any health-care professional who treats you. Use tamoxifen regularly for best results. You may need to be on tamoxifen for up to 5 years. 

Do not use tamoxifen if you: are allergic, have a history of blood clots, are taking a blood thinner, or if you are pregnant. Inform your doctor if you become pregnant or breast-feed. Use a barrier form of birth control while on this drug for at least after 2 months after your treatment. Tamoxifen may affect the effectiveness of hormonal birth control methods. Inform your doctor of your medical history before starting this drug, especially if you have liver disease, high triglycerides, cataract history, or history of stroke or blood clots. Inform your doctor if you are undergoing chemotherapy or radiation treatment. Avoid grapefruit products. Tamoxifen may increase your risk of uterine cancer, stroke, or a blood clot in the lung, all of which are fatal. Caregivers should wear gloves if they come into contact with the patient’s bodily fluids. This includes washing soiled clothing separately.

Seek emergency medical attention if you suspect an overdose or allergic reaction. Contact your doctor immediately if you experience a serious side effect, such as: signs of a stroke, signs of a blood clot in your lung or leg, vision problems, unusual vaginal bleeding/discharge, change in your menstrual periods, pain or pressure in your pelvis, a new lump in the breast, signs of liver problems, and signs of high calcium levels in your blood. Other side effects may include: hot flashes, weight loss, and menstrual changes. Other drugs may interact with tamoxifen.