Tamoxifen

Say it: ta-MOX-ih-fen · Brand names: Soltamox

Tamoxifen is a hormone therapy pill that blocks estrogen from feeding breast cancer cells.

What it is

Many breast cancers use the hormone estrogen to grow. Tamoxifen attaches to the estrogen receptor on breast cancer cells so estrogen cannot use it. It can be used before or after menopause, and in men.

Often used for

• hormone receptor positive breast cancer, to lower the chance it comes back after surgery
• hormone receptor positive breast cancer that has spread
• ductal carcinoma in situ (DCIS), an early breast cancer
• lowering the chance of breast cancer in people at high risk

How you get it

Tamoxifen is a pill (or liquid) you take by mouth at home, once or twice a day, with or without food. It is often taken for 5 to 10 years. Your schedule may be different.

Common side effects and what helps

• Hot flashes or night sweats. Dress in layers, keep your room cool, and limit caffeine and alcohol.
• Vaginal discharge or dryness. Ask your team about safe moisturizers.
• Changes in your periods. Tell your team about any new bleeding.
• Swelling in your hands or feet. Raise your legs when you sit.
• Feeling sick to your stomach or throwing up. Eat small meals and ask your team about anti-nausea medicine.
• Mood changes or feeling tired. Talk with your team if this is hard to manage.
• Leg cramps. Stretching and fluids may help.

Call your care team right away if you have

• Swelling, pain, or warmth in one leg, or sudden shortness of breath
• Chest pain or coughing up blood
• Sudden weakness or numbness of the face, arm, or leg, trouble speaking, or a sudden very bad headache
• Vaginal bleeding that is new or not normal for you, or pain or pressure in your pelvis
• Changes in your eyesight
• Yellow skin or eyes, dark tea colored urine, or pain on the right side of your belly

Before you start, tell your team

• If you are pregnant, may become pregnant, or are breastfeeding
• If you have had blood clots or a stroke
• If you take a blood thinner such as warfarin
• If you take an antidepressant, since some can make tamoxifen work less well
• All the medicines, vitamins, and herbal products you take, since some can change how this medicine works

Good to know

• It can raise the chance of cancer of the uterus. Get any unusual vaginal bleeding checked, and keep up with your gynecology visits.
• It can raise the chance of blood clots and stroke.
• It can cause cataracts. Tell your team about any eyesight changes.
• Use a non hormone birth control during treatment and for 2 months after, if pregnancy is possible. Ask your team which kind is right for you.

At home

• Take it at about the same time each day.
• Swallow the tablets whole with water. If you take the liquid, measure it with the dosing cup from the pharmacy.
• If you miss a dose or throw up after taking it, ask your team what to do. Do not take extra pills to make up for it.
• Store at room temperature, away from children and pets.

Questions to ask

• How long will I take this medicine?
• How often do I need gynecology checkups?
• Are my other medicines, especially antidepressants, safe with tamoxifen?
• What can I do about hot flashes?

Side effect guides

• Fatigue (tiredness)
• Nausea and vomiting
• Low platelets and bleeding

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.