Tamoxifen is used to treat breast cancer. It is also used to reduce the chances of breast cancer in high-risk patients.

This medication can block the growth of breast cancer. It works by interfering with the effects of estrogen in the breast tissue.

Read the Medication Guide provided by your pharmacist before you start using tamoxifen and each time you get a refill. If you have any questions, consult your doctor or pharmacist.

Take this medication by mouth with or without food as directed by your doctor, usually once or twice daily for 5 years. Daily dosages greater than 20 milligrams are usually divided in half and taken twice a day, in the morning and evening, or as directed by your doctor. If you are using the liquid, measure the dose carefully using a special measuring device/spoon. Do not use a household spoon because you may not get the correct dose.

Dosage is based on your medical condition and response to treatment. The duration of treatment to prevent cancer from returning may be between 5 to 10 years, depending on your medical condition and response to treatment.

Use this medication regularly to get the most benefit from it. To help you remember, take it at the same time(s) each day.

If you have breast cancer that has spread to other parts of the body, you may experience increased bone/cancer pain and/or disease flare-up as you start taking tamoxifen. In some cases, this may be a sign of a good response to the medication. Symptoms include increased bone pain, increased tumor size, or even new tumors. These symptoms usually disappear quickly. Always tell your doctor right away about these symptoms.

Since this drug can be absorbed through the skin and lungs, women who are pregnant or who may become pregnant should not handle this medication or breathe the dust from the tablets. (See also Precautions section.)

Tell your doctor right away if your condition gets worse (such as you get new breast lumps).

See also Warning section.

Hot flashes, nausea, leg cramps, muscle aches, hair thinning, headache, and numb/tingling skin may occur. A loss of sexual ability/interest may occur in men. If these effects last or get worse, tell your doctor promptly.

Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if you have any serious side effects, including:

• vision changes (such as blurred vision)
• eye pain
• easy bruising/bleeding
• mental/mood changes
• swelling of ankles/feet
• unusual tiredness
• signs of infection (such as sore throat that doesn't go away, fever)
• signs of liver disease (such as nausea/vomiting that doesn't stop, loss of appetite, stomach/abdominal pain, yellowing eyes/skin, dark urine)

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including:

• rash
• itching/swelling (especially of the face/tongue/throat)
• severe dizziness
• trouble breathing

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Before taking tamoxifen, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of:

• blood clots (such as deep vein thrombosis, pulmonary embolism, stroke)
• certain heart problems (fast/slow/irregular heartbeat, QT prolongation in the EKG)
• high cholesterol/triglycerides
• limited or no ability to walk (immobility)
• diabetes
• high blood pressure
• smoking
• cataracts
• liver disease

Before having surgery (especially breast reconstruction), tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Tell your doctor if you are pregnant or plan to become pregnant. You should not become pregnant while using tamoxifen. Tamoxifen may harm an unborn baby. Women using this medication should ask about reliable non-hormonal forms of birth control (such as condoms, diaphragms with spermicide) during treatment and for 2 months after the last dose. Men using this medication should ask about reliable forms of birth control during treatment and for 6 months after the last dose. If you or your partner becomes pregnant, talk to your doctor right away about the risks and benefits of this medication.

It is unknown if this medication passes into breast milk. Because of the possible risk to the infant, breastfeeding is not recommended while using this medication and for 3 months after the last dose. Consult your doctor before breastfeeding.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Some products that may interact with this drug are:

• anastrozole
• "blood thinners" (such as warfarin)
• estrogens
• letrozole
• hormonal forms of birth control (such as birth control pills, patches, implants)
• ribociclib

Other medications can affect the removal of tamoxifen from your body, which may affect how tamoxifen works. Examples include butalbital, cimetidine, mitotane, rifamycins (such as rifampin), secobarbital, SSRI antidepressants (such as fluoxetine, paroxetine), St. John's wort, drugs used to treat seizures (such as carbamazepine, phenobarbital, phenytoin, primidone), among others.

This medication may interfere with certain lab tests (such as thyroid tests), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.

If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call 1-800-222-1222. Canada residents can call 1-844-764-7669. Symptoms of overdose may include: shaking, unsteady walking, fainting, or fast/irregular heartbeat.

Do not share this medication with others.

Lab and/or medical tests (such as complete blood count, liver/heart function, pelvic exams, mammogram, eye exams) should be done while you are taking this medication. Keep all medical and lab appointments. Consult your doctor for more details.

If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.

Store at room temperature away from light and moisture. Do not store in the bathroom. If you are using the liquid, do not refrigerate or freeze it. Once the liquid bottle is opened, the medication expires after 3 months. Keep all medications away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company.