Tamoxifen is a prescription medication used to treat breast cancer and lower the the chance of developing breast cancer. Certain types of breast cancers need estrogen to grow. Tamoxifen belongs to a group of drugs called anti-estrogens, which can block estrogen’s effects, slowing the growth of cancer cells.
This medication comes in a tablet and an oral solution and is usually taken once or twice a day.
Common side effects of tamoxifen include hot flashes and vaginal discharge.
For Women with Ductal Carcinoma in Situ (DCIS) and Women at High Risk for Breast Cancer: Serious and life-threatening events associated with tamoxifen in the risk reduction setting (women at high risk for cancer and women with DCIS) include uterine malignancies, stroke and pulmonary embolism. Incidence rates for these events were estimated from the NSABP P-1 trial. Uterine malignancies consist of both endometrial adenocarcinoma (incidence rate per 1,000 women-years of 2.20 for tamoxifen vs 0.71 for placebo) and uterine sarcoma (incidence rate per 1,000 women-years of 0.17 for Nolvadex vs 0.04 for placebo)*. For stroke, the incidence rate per 1,000 women-years was 1.43 for Nolvadex vs 1.00 for placebo**. For pulmonary embolism, the incidence rate per 1,000 women-years was 0.75 for tamoxifen versus 0.25 for placebo**.
Some of the strokes, pulmonary emboli, and uterine malignancies were fatal.
Health care providers should discuss the potential benefits versus the potential risks of these serious events with women at high risk of breast cancer and women with DCIS considering tamoxifen to reduce their risk of developing breast cancer.
The benefits of tamoxifen outweigh its risks in women already diagnosed with breast cancer.
*Updated long-term follow-up data (median length of follow-up is 6.9 years) from NSABP P-1 study.
Tamoxifen is a prescription medicine used:
- to lower the chance of getting breast cancer in women with a higher than normal chance of getting breast cancer in the next 5 years (high-risk women)
- to lower the chance of getting invasive (spreading) breast cancer in women who had surgery and radiation for ductal carcinoma in situ (DCIS). DCIS means the cancer is only inside the milk ducts
- to treat breast cancer in women after they have finished early treatment. Early treatment can include surgery, radiation, and chemotherapy
- in women and men, to treat breast cancer that has spread to other parts of the body (metastatic breast cancer)
This medication may be prescribed for other uses. Ask your doctor or pharmacist for more information.
- The most common side effect of tamoxifen is hot flashes. This is not a sign of a serious problem.
- The next most common side effect is vaginal discharge. If the discharge is bloody, it could be a sign of a serious problem.
Less common but serious side effects of tamoxifen are listed below. These can occur at any time. Call your doctor right away if you have any signs of side effects listed below:
Changes in the lining (endometrium) or body of your uterus. These changes may mean serious problems are starting, including cancer of the uterus. The signs of changes in the uterus are:
- Vaginal bleeding or bloody discharge that could be a rusty or brown color. You should call your doctor even if only a small amount of bleeding occurs.
- Change in your monthly bleeding, such as in the amount or timing of bleeding or increased clotting.
- Pain or pressure in your pelvis (below your belly button).
Blood clots in your veins or lungs. These can cause serious problems, including death. You may get clots up to 2-3 months after you stop taking tamoxifen. The signs of blood clots are:
- sudden chest pain, shortness of breath, coughing up blood
- pain, tenderness, or swelling in one or both of your legs
Stroke. Stroke can cause serious medical problems, including death. The signs of stroke are:
- sudden weakness, tingling, or numbness in your face, arm or leg, especially on one side of your body
- sudden confusion, trouble speaking or understanding
- sudden trouble seeing in one or both eyes
- sudden trouble walking, dizziness, loss of balance or coordination
- sudden severe headache with no known cause
Cataracts or increased chance of needing cataract surgery. The sign of these problems is slow blurring of your vision.
Liver problems, including jaundice. The signs of liver problems include lack of appetite and yellowing of your skin or whites of your eyes.
Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements. Especially tell your doctor if you take:
- aminoglutethimide (Cytadren);
- anastrazole (Arimidex);
- bromocriptine (Parlodel);
- cancer chemotherapy medication such as cyclophosphamide (Cytoxan, Neosar) letrozole (Femara);
- medroxyprogesterone (Depo-Provera, Provera, in Prempro);
- rifampin (Rifadin, Rimactane)
This is not a complete list of tamoxifen drug interactions. Ask your doctor or pharmacist for more information.
Do not take tamoxifen for any reason if you:
- Are pregnant or plan to become pregnant while taking tamoxifen or during the 2 months after you stop taking tamoxifen. Tamoxifen may harm your unborn baby. It takes about 2 months to clear tamoxifen from your body. To be sure you are not pregnant, you can start taking tamoxifen while you are having your menstrual period. Or, you can take a pregnancy test to be sure you are not pregnant before you begin.
- Are breastfeeding. We do not know if tamoxifen can pass through your milk and harm your baby.
- Have had an allergic reaction to tamoxifen or to any of its inactive ingredients.
- If you get pregnant while taking tamoxifen, stop taking it right away and contact your doctor. Tamoxifen may harm your unborn baby.
Do not take tamoxifen to lower your chance of getting breast cancer if:
- You ever had a blood clot that needed medical treatment.
- You are taking medicines to thin your blood, like warfarin, also called Coumadin.
- Your ability to move around is limited for most of your waking hours.
- You are at risk for blood clots. Your doctor can tell you if you are at high risk for blood clots.
- You do not have a higher than normal chance of getting breast cancer. Your doctor can tell you if you are a high-risk woman.
Medicines can interact with certain foods. In some cases, this may be harmful and your doctor may advise you to avoid certain foods. In the case of tamoxifen there are no specific foods that you must exclude from your diet when receiving tamoxifen.
Tell your doctor if you:
- are allergic to any ingredient in tamoxifen.
- have ever had a blood clot in the lungs or legs, a stroke, or a heart attack (see Black Box Warning).
- have high blood pressure.
- have diabetes.
- take blood thinners such as warfarin (Coumadin).
- have high cholesterol.
- are pregnant or breastfeeding.
Tell your doctor about all the prescription medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements.
Tell your doctor if you are pregnant or plan to become pregnant while taking tamoxifen or during the 2 months after you stop taking tamoxifen. Tamoxifen may harm your unborn baby. It takes about 2 months to clear tamoxifen from your body. To be sure you are not pregnant, you can start taking tamoxifen while you are having your menstrual period. Or, you can take a pregnancy test to be sure you are not pregnant before you begin.
Tell your doctor if you are breastfeeding or plan to breastfeed. It is not known if tamoxifen is excreted in human breast milk or if it will harm your nursing baby.
- Tamoxifen is available in a tablet and in an oral solution.
- Take your medicine every day. It may be easier to remember if you take it at the same time each day.
- If you forget a dose, take it when you remember, then take the next dose as usual. If it is almost time for your next dose or you remember at your next dose, do not take extra tablets to make up the missed dose.
- Take tamoxifen for 5 years, unless your doctor tells you otherwise.
- Swallow the tablet(s) whole, with water or another non-alcoholic liquid. You can take tamoxifen with or without food.
Tamoxifen Oral Solution:
- Follow the directions on your prescription label carefully.
- 20 mg of tamoxifen is administered as 10 mL (equivalent to 2 teaspoons).
- Use the appropriate measuring device to measure solution
Take tamoxifen exactly as prescribed by your doctor. Follow the directions on your prescription label carefully. Your doctor will determine the best dose for you.
For patients with breast cancer, the recommended daily dose is 20-40 mg. Dosages greater than 20 mg per day should be given in divided doses (morning and evening).
Ductal Carcinoma in Situ (DCIS): The recommended dose is tamoxifen 20 mg daily for 5 years.
- A 20 mg dose of tamoxifen oral solution is administered as 10 mL (equivalent to 2 teaspoons).
Reduction in Breast Cancer Incidence in High Risk Women: The recommended dose is tamoxifen 20 mg daily for 5 years. There are no data to support the use of tamoxifen other than for 5 years.
If you take too much tamoxifen, call your local Poison Control Center or seek emergency medical attention right away.
- Have regular gynecology check-ups, breast exams and mammograms. Your doctor will tell you how often. These will check for signs of breast cancer and cancer of the endometrium (lining of the uterus). Because tamoxifen does not prevent all breast cancers, and you may get other types of cancers, you need these exams to find any cancers as early as possible.
- Tell all of the doctors that you see that you are taking tamoxifen.
- Tell your doctor right away if you have any new breast lumps.
- Store tamoxifen at controlled room temperature, 20-25°C (68-77°F).
Tamoxifen Oral Solution:
- Store at temperatures up to 25°C (77°F).
- DO NOT freeze or refrigerate.
- Store in original packaging in order to protect from light. Use within 3 months of opening.
Keep this and all medicines out of reach of children.
Take tamoxifen for 5 years, unless your doctor tells you otherwise.
Because tamoxifen does not prevent all breast cancers, and you may get other types of cancers, you need these exams to find any cancers as early as possible.
The most common side effect of tamoxifen is hot flashes. This is not a sign of a serious problem.The next most common side effect is vaginal discharge. If the discharge is bloody, it could be a sign of a serious problem.
Tell your doctor if you are pregnant or plan to become pregnant while taking tamoxifen or during the 2 months after you stop taking tamoxifen.
- Tamoxifen may harm your unborn baby. It takes about 2 months to clear tamoxifen from your body.
- To be sure you are not pregnant, you can start taking tamoxifen while you are having your menstrual period.
Breast cancer is cancer that forms in the cells of the breasts. The development of breast cancer is strongly related to the amount of estrogen the breast is exposed to over time. Some women have hormone receptor positive (ER/PR+) breast cancer. Estrogen receptors are proteins found on the surface of cells. Cancer cells grow in response to estrogen binding to these receptors. Tamoxifen lowers the amount of estrogen in the blood, limiting the amount of estrogen available to bind to these receptors. This slows or stops the growth of cancer cells.
Hormone receptor testing is done to determine how likely it is that tamoxifen will be an effective treatment. Patients who do not have hormone receptor positive breast cancer are not likely to respond to treatment with tamoxifen.