How does this medication work? What will it do for me?
Tamoxifen belongs to the group of cancer-fighting medications known as antineoplastics, and specifically to the type of antineoplastics known as antiestrogens. It is used in combination with other medications to treat early breast cancer.
Tamoxifen fights certain types of breast cancer, called hormone responsive or estrogen receptor positive breast cancer, by blocking the effects of the hormone estrogen in the body. This prevents the growth of the types of breast cancer cells that require estrogen for growth and survival. It is also used to treat breast cancer that is advanced or has spread to other parts of the body.
This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.
Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.
Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.
What form(s) does this medication come in?
Mylan-Tamoxifen is no longer being manufactured for sale in Canada. For brands that may still be available, search under tamoxifen. This article is being kept available for reference purposes only. If you are using this medication, speak with your doctor or pharmacist for information about your treatment options.
How should I use this medication?
The recommended dose of tamoxifen is 20 mg to 40 mg daily taken in 1 dose or in 2 divided doses. It may be taken with or without food. For the treatment of early breast cancer, the recommended duration of treatment is 5 years.
Tamoxifen sometimes causes nausea, but it is important to keep taking the medication even if you begin to feel ill, unless otherwise directed by the doctor. Do not stop taking tamoxifen unless you discuss it with your doctor first.
Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a different dose than the ones listed here, do not change the way that you are taking the medication without consulting your doctor.
It is important to that this medication be taken exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.
Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.
Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.
Who should NOT take this medication?
Do not take tamoxifen if you:
- are allergic to tamoxifen or any ingredients of the medication
- are pregnant or planning to become pregnant
What side effects are possible with this medication?
Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.
The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.
The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.
Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.
- bone pain
- changes in menstrual period
- genital itching
- hair loss (partial) or hair thinning
- hot flashes
- leg cramps
- mild nausea and vomiting
- muscle pain
- skin rash
- swelling of the feet, ankles, or lower leg
- taste alterations
- tiredness and weakness
Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.
Check with your doctor as soon as possible if any of the following side effects occur:
- abdominal pain, bloating, or swelling
- blurred vision or vision changes
- cough and shortness of breath
- increased pain or growth of tumour
- numbness or tingling of the skin
- pain or feeling of pressure in the pelvis
- severe nausea or vomiting
- signs of anemia (low red blood cells; e.g., dizziness, pale skin, unusual tiredness or weakness, shortness of breath)
- signs of bleeding (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don't stop bleeding)
- signs of depression (e.g., poor concentration, changes in weight, changes in sleep, decreased interest in activities, thoughts of suicide)
- signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
- skin changes (e.g., rash, redness or blisters on exposed skin; raised red or purple patches with blisters or crusting in the centre; itching or burning sensations)
- symptoms of inflammation of the pancreas (e.g., severe upper right abdominal pain)
- symptoms of low white blood cells (infection; fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness)
- symptoms of lung inflammation (e.g., shortness of breath, cough)
- vaginal growths, bleeding, or discharge
Stop taking the medication and seek immediate medical attention if any of the following occur:
- blistering, peeling, or loosening of the skin or mucous membranes
- signs of a severe allergic reaction (e.g., hives; difficulty breathing; swelling of the face, lips, tongue, or throat)
- swelling of the hands, feet, or ankles
- symptoms of a blood clot in the leg (e.g., pain, swelling or redness of the calf or leg)
- symptoms of a blood clot in the lungs (e.g., chest pain and shortness of breath)
- symptoms of a stroke (e.g., sudden weakness or numbness of the arms or legs, sudden difficulty speaking, sudden dizziness, sudden severe headache)
Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.
Are there any other precautions or warnings for this medication?
Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.
Blood clots: Tamoxifen may increase the chance of developing blood clots in the lungs or legs. This chance may be further increased if tamoxifen is given with other forms of chemotherapy. If you have a history of blood clots, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.
A blood clot in the blood vessels of the brain can prevent blood from reaching parts of the brain, causing a stroke. If you experience signs of a stroke such as confusion, difficulty speaking, loss of coordination, sudden headache or vision changes, contact your doctor as soon as possible.
Cataracts: Tamoxifen may cause cataracts or worsen existing cataracts for some people. If you experience any vision changes while taking this medication, contact your doctor.
Drowsiness/weakness: Tamoxifen can cause fatigue and weakness, which in turn can affect the mental or physical abilities needed to drive or operate machinery. Avoid driving, operating machinery, or performing other potentially hazardous tasks until you have determined how this medication affects you.
High blood calcium levels: Tamoxifen may cause an increase in blood calcium levels for women with breast cancer that has spread to other parts of the body. Your doctor will monitor for this with blood tests.
Liver function: Tamoxifen may affect liver function and rarely can cause liver failure. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking this medication.
Uterine cancers: Tamoxifen may increase the chance of developing certain types of uterine cancer. Talk to your doctor about whether any special monitoring is needed. If you experience any vaginal bleeding while or after taking this medication, contact your doctor immediately.
White blood cells and platelets: People with low white blood cells or platelets should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.
Worsening symptoms: For some women taking this medication, pain may worsen and the size of the affected tissue may increase at the beginning of treatment. This usually resolves within a few weeks of starting tamoxifen. If you experience these effects, contact your doctor.
Pregnancy: This medication may cause birth defects or death to the developing fetus and should not be used during pregnancy. Effective birth control should be used while taking this medication and for 9 months after finishing it. Tell the doctor immediately if you become pregnant while taking this medication.
Breast-feeding: It is not known if tamoxifen passes into breast milk. If you are breast-feeding and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.
Children: The safety and effectiveness of using this medication have not been established for children.
What other drugs could interact with this medication?
There may be an interaction between tamoxifen and any of the following:
- antipsychotics (e.g., chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone, thioridazine)
- "azole" antifungal medications (e.g., fluconazole, ketoconazole, voriconazole)
- HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., efavirenz, etravirine, nevirapine)
- lumacaftor and ivacaftor
- macrolide antibiotics (e.g., clarithromycin, erythromycin)
- milk thistle
- other cancer medications (e.g., capecitabine, doxorubicin, fluorouracil, methotrexate, paclitaxel)
- protein kinase inhibitors (e.g., crizotinib, dabrafenib, dasatinib, imatinib, nilotinib, vandetanib)
- St. John's wort
- selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine, paroxetine, sertraline)
If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:
- stop taking one of the medications,
- change one of the medications to another,
- change how you are taking one or both of the medications, or
- leave everything as is.
An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.
Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.
All material copyright MediResource Inc. 1996 – 2023. Terms and conditions of use. The contents herein are for informational purposes only. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Source: www.medbroadcast.com/drug/getdrug/Mylan-Tamoxifen