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 Tamoxifen. If you are concerned about side effects, discuss the risks and benefits of Tamoxifen with your doctor.

The following side effects have been reported by at least 1% of people taking Tamoxifen. 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
• Constipation
• Diarrhea
• genital itching
• hair loss (partial) or hair thinning
• headache
• hot flashes
• leg cramps
• lightheadedness
• 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:

• 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 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)
• 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)
• 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
• Hives
• signs of a Anaphylaxis (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 Tamoxifen.

10 mg
Each white-to-off-white, round, biconvex, film-coated tablet engraved "N" over "10" on same side, and plain on the other side, contains tamoxifen citrate equivalent to 10 mg of tamoxifen. Nonmedicinal ingredients: colloidal silicon dioxide, diacetylated monoglycerides, ethylcellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose, magnesium stearate, mannitol, povidone, sodium starch glycolate, and titanium dioxide.

20 mg
Each white-to-off-white, round, biconvex, film-coated tablet engraved on one side, "N" over scoreline, "20" under it, and plain on the other side, contains tamoxifen citrate equivalent to 20 mg of tamoxifen. Nonmedicinal ingredients: colloidal silicon dioxide, diacetylated monoglycerides, ethylcellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose, magnesium stearate, mannitol, povidone, sodium starch glycolate, and titanium dioxide. Gluten- and tartrazine-free.

Do not take tamoxifen if you:

• are allergic to tamoxifen or any ingredients of the medication
• are pregnant or planning to become pregnant

There may be an interaction between tamoxifen and any of the following:

• Amiodarone
• Anagrelide
• Anastrozole
• angiotensin receptor blockers (ARBs; e.g., candasartan, Irbesartan, Losartan)
• antipsychotics (e.g., Chlorpromazine, Clozapine, Haloperidol, Olanzapine, Quetiapine, Risperidone)
• Aprepitant
• asunaprevir
• "azole" antifungal medications (e.g., fluconazole, ketoconazole, Voriconazole)
• barbiturates (e.g., Phenobarbital, secobarbital)
• Bosentan
• Bupropion
• calcium channel blockers (e.g., Amlodipine, Diltiazem, Nifedipine, Verapamil)
• Carbamazepine
• chloroquine
• Cinacalcet
• conivaptan
• Darifenacin
• Deferasirox
• Disopyramide
• dofetilide
• Domperidone
• Dronedarone
• estrogens (e.g., conjugated estrogen, Estradiol, ethinyl estradiol)
• Flecainide
• Gemfibrozil
• HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., delavirdine, efavirenz, etravirine, nevirapine)
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• hydroxychloroquine
• Leflunomide
• Letrozole
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• Methadone
• mifepristone
• milk thistle
• Mirabegron
• nefazodone
• Omeprazole
• other cancer medications (e.g., Capecitabine, Doxorubicin, Fluorouracil, Methotrexate, Paclitaxel)
• Phenytoin
• Pimozide
• Pioglitazone
• primidone
• procainamide
• protein kinase inhibitors (e.g., Crizotinib, Dasatinib, imatinib, Nilotinib)
• quinidine
• quinine
• quinolone antibiotics (e.g., ciprofloxacin, Norfloxacin, Ofloxacin)
• Repaglinide
• rifabutin
• rifampin
• Rosiglitazone
• St. John's wort
• selective serotonin reuptake inhibitors (SSRIs; e.g., Citalopram, Fluoxetine, Paroxetine, Sertraline)
• serotonin antagonists (anti-emetic medications; e.g., Granisetron, Ondansetron)
• simeprevir
• Sotalol
• "statin" anti-cholesterol medications (e.g., Atorvastatin, Lovastatin, Simvastatin)
• "sulfa" antibiotics (e.g., sulfadiazine, sulfamethoxazole, sulfisoxazole)
• terbinafine
• Tetrabenazine
• Tocilizumab
• Tolbutamide
• tretinoin (systemic)
• tricyclic antidepressants (e.g., Clomipramine, Desipramine, Trimipramine)
• Trimethoprim
• Warfarin
• Zafirlukast

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 Tamoxifen. 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.

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 Tamoxifen.

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 Tamoxifen may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tamoxifen, 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 Tamoxifen, contact your doctor.

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.

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 Tamoxifen, contact your doctor immediately.

White blood cells and platelets: People with low white blood cells or platelets should discuss with their doctor how Tamoxifen may affect their medical condition, how their medical condition may affect the dosing and effectiveness of Tamoxifen, and whether any special monitoring is needed.

Worsening symptoms: For some women taking Tamoxifen, 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: Tamoxifen 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 Tamoxifen and for about 2 months after finishing it. Tell the doctor immediately if you become pregnant while taking Tamoxifen.

Breast-feeding: It is not known if tamoxifen passes into breast milk. If you are a breast-feeding mother and are taking Tamoxifen, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using Tamoxifen have not been established for children.

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.

Tamoxifen may be available under multiple brand names and/or in several different forms. Any specific brand name of Tamoxifen may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of Tamoxifen may not be used for all of the conditions discussed here.

Your doctor may have suggested Tamoxifen 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 Tamoxifen, speak to your doctor. Do not stop taking Tamoxifen without consulting your doctor.

Do not give Tamoxifen to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take Tamoxifen if their doctor has not prescribed it.