What is tamoxifen?
Tamoxifen blocks the actions of estrogen, a female hormone. Certain types of breast cancer require estrogen to grow.
Tamoxifen is used to treat some types of breast cancer in men and women. It is also used to lower a woman’s chance of developing breast cancer if she has a high risk (such as a family history of breast cancer).
Tamoxifen may also be used for purposes not listed in this medication guide.
Do not use tamoxifen if you are pregnant. It could harm the unborn baby. Use a barrier form of birth control (such as a condom or diaphragm with spermicide) while you are using this medication and for at least 2 months after your treatment ends. You should not use tamoxifen if you are allergic to it, if you have a history of blood clots in your veins or your lungs, or if you are taking a blood thinner such as warfarin (Coumadin).
Before using this medicine, tell your doctor if you have liver disease, high triglycerides (a type of fat in the blood), a history of cataract, or a history of stroke or blood clot. Also tell your doctor if you if you are receiving chemotherapy or radiation treatment.
If you are taking tamoxifen to reduce your risk of breast cancer, you may need to take your first dose while you are having a menstrual period. You may also need to have a pregnancy test before you start taking this medicine, to make sure you are not pregnant. Follow your doctor’s instructions.
Taking tamoxifen may increase your risk of uterine cancer, stroke, or a blood clot in the lung, which can be fatal. Talk with your doctor about your specific risks in taking this medication.
To make sure this medication is not causing harmful effects, your doctor may want you to have mammograms and to perform routine breast self-exams on a regular basis. Your liver function may also need to be tested. Visit your doctor regularly.
Before taking this medicine
You should not use tamoxifen if you are allergic to it.
You should not use tamoxifen to reduce your risk of breast cancer if you are also taking a blood thinner such as warfarin (Coumadin, Jantoven).
Do not take tamoxifen if you are pregnant. It could harm the unborn baby. Avoid becoming pregnant while you are using this medicine, and for at least 2 months after your treatment ends.
Hormonal contraception (such as birth control pills, injections, implants, skin patches, and vaginal rings) may not be effective enough to prevent pregnancy while taking tamoxifen. Use barrier or non-hormonal birth control (examples: condom, diaphragm with spermicide, or intrauterine device/IUD).
If you are taking tamoxifen to reduce your risk of breast cancer, you may need to take your first dose while you are having a menstrual period. You may also need to have a pregnancy test before you start taking tamoxifen, to make sure you are not pregnant. Follow your doctor’s instructions.
Taking tamoxifen may increase your risk of uterine cancer, stroke, or a blood clot in the lung, which can be fatal. Talk with your doctor about your specific risks in taking this medicine.
To make sure tamoxifen is safe for you, tell your doctor if you have:
- a history of stroke or blood clot;
- liver disease;
- high cholesterol or triglycerides (a type of fat in the blood);
- a history of cataracts; or
- if you are receiving chemotherapy or radiation.
It is not known whether tamoxifen passes into breast milk or if it could harm a nursing baby. This medicine has been shown to slow breast milk production. Do not breast-feed while taking tamoxifen.
How should I take tamoxifen?
Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.
Measure liquid medicine with the dosing syringe provided, or with a special dose-measuring spoon or medicine cup. If you do not have a dose-measuring device, ask your pharmacist for one.
Tamoxifen can be taken with or without food.
While using tamoxifen, you may need frequent blood tests.
If you need surgery or medical tests or if you will be on bed rest, you may need to stop using this medicine for a short time. Any doctor or surgeon who treats you should know that you are taking tamoxifen.
Have regular physical exams and mammograms, and self-examine your breasts for lumps on a monthly basis while using this medicine.
Use tamoxifen regularly to get the most benefit. Get your prescription refilled before you run out of medicine completely. You may need to keep using this medication for up to 5 years.
Store at room temperature away from moisture, heat, or cold. Do not freeze.
Detailed Tamoxifen dosage information
What happens if I miss a dose?
Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.
What to avoid
This medicine can pass into body fluids (urine, feces, vomit). Caregivers should wear rubber gloves while cleaning up a patient’s body fluids, handling contaminated trash or laundry or changing diapers. Wash hands before and after removing gloves. Wash soiled clothing and linens separately from other laundry.
Avoid grapefruit and grapefruit juice while taking tamoxifen.
Tamoxifen side effects
Get emergency medical help if you have signs of an allergic reaction to tamoxifen: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
Tamoxifen can increase your risk of stroke or blood clots. Call your doctor at once if you have:
- signs of a stroke – sudden numbness or weakness (especially on one side of the body), sudden severe headache, slurred speech, problems with vision or balance;
- signs of a blood clot in the lung – chest pain, sudden cough, wheezing, rapid breathing, coughing up blood; or
- signs of a blood clot in your leg – pain, swelling, warmth, or redness in one or both legs.
Also call your doctor at once if you have:
- blurred vision, tunnel vision, eye pain, or seeing halos around lights;
- unusual vaginal bleeding or discharge;
- changes in your menstrual periods;
- pain or pressure in your pelvic area;
- a new breast lump;
- liver problems – nausea, upper stomach pain, itching, tired feeling, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes); or
- high levels of calcium in your blood – vomiting, constipation, increased thirst or urination, muscle weakness, bone pain, confusion, lack of energy, or tired feeling.
Common tamoxifen side effects may include:
- hot flashes;
- menstrual changes;
- vaginal discharge; or
- weight loss.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
What other drugs will affect tamoxifen?
Many drugs can interact with tamoxifen, and some drugs should not be used together. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide. Tell your doctor about all medicines you use, and those you start or stop using during your treatment with tamoxifen. Give a list of all your medicines to any healthcare provider who treats you.
Tamoxifen drug interactions (more detail)