In the U.S.—

In Canada—

• Antineoplastic

Tamoxifen ( ta-MOX-i-fen) is a medicine that blocks the effects of the estrogen hormone in the body. It is used to treat breast cancer in women or men. It may also be used to treat other kinds of cancer, as determined by your doctor.

Tamoxifen also may be used to reduce the risk of developing breast cancer in women who have a high risk of developing breast cancer. Women at high risk for developing breast cancer are at least 35 years of age and have a combination of risk factors that make their chance of developing breast cancer 1.67% or more over the next 5 years. Your doctor will help to determine your risk of developing breast cancer.

The following are risk factors that may increase your chance of developing breast cancer:
• If you have close family members (mother, sister, or daughter) with breast cancer
• If you have ever had a breast biopsy or if high-risk changes in your breast(s) have been found from a breast biopsy
• If you have never been pregnant or if your first pregnancy occurred at a late age
• If your first menstrual period occurred at an early age

The exact way that tamoxifen works against cancer is not known, but it may be related to the way it blocks the effects of estrogen on the body.

Before you begin treatment with tamoxifen, you and your doctor should talk about the good this medicine will do as well as the risks of using it.

Tamoxifen is available only with your doctor's prescription, in the following dosage form:

Oral
• Tablets (U.S. and Canada)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For tamoxifen, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to tamoxifen.

Pregnancy—Tell your doctor if you are pregnant or if you intend to become pregnant. Tamoxifen should not be used to reduce the risk of breast cancer if you are pregnant of if you intend to become pregnant. Tamoxifen use in women has been shown to cause miscarriages, birth defects, death of the fetus, and vaginal bleeding. Studies in rats and rabbits have shown that tamoxifen causes miscarriages, death of the fetus, and slowed learning. Studies in animals also have shown that tamoxifen may cause some of the same problems as those caused by an estrogen called diethylstilbestrol (DES). DES causes genital tract problems and, rarely, an increased risk of cancer of the cervix or vagina in daughters of women who took it during their pregnancy. It is not known whether tamoxifen causes these same problems.

Be sure that you have discussed this with your doctor before taking this medicine. It is best to use some kind of birth control while you are taking tamoxifen and for about 2 months after you stop taking it. However, do not use oral contraceptives (“the Pill”) since they may interfere with this medicine. Tell your doctor right away if you think you have become pregnant while taking tamoxifen.

Breast-feeding—Because this medicine may cause serious side effects, breast-feeding is generally not recommended while you are taking it.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults. Although there is no specific information comparing use of tamoxifen in the elderly with use in other age groups, this medicine is not expected to cause different side effects or problems in older people than it does in younger adults.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. Tell your health care professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine. If you are taking tamoxifen to reduce the risk of breast cancer, it is especially important that your health care professional know if you are taking the following:

• Anticoagulant, coumarin-type (blood thinners)—Blood thinners (e.g., warfarin [Coumadin]) should not be used with tamoxifen when used to reduce the risk of developing breast cancer in women who have a high risk of developing breast cancer. If you need to take blood thinners, your blood clotting times should be monitored by your doctor.

• Cytotoxic medicines—These are medicines that damage cells. If you take these medicines with tamoxifen, you may have an increased risk of blood clots.

For all patients
• Blood problems or
• Cataracts or other eye problems—Tamoxifen may also cause these problems

• High cholesterol levels in the blood—Tamoxifen can increase cholesterol levels

When used for reducing the risk for developing breast cancer in high-risk women or in women with Ductal Carcinoma in Situ (DCIS)
• Blood clots (or history of) or
• Pulmonary embolism (or history of) or
• Stroke or
• Uterine (womb) cancer—May increase risk of serious side effects from tamoxifen.

Use this medicine only as directed by your doctor. Do not use more or less of it, and do not use it more often than your doctor ordered. The exact amount of medicine you need has been carefully worked out. Taking too much may increase the chance of side effects, while taking too little may not improve your condition.

Tamoxifen sometimes causes mild nausea and vomiting. However, it may have to be taken for several weeks or months to be effective. Even if you begin to feel ill, do not stop using this medicine without first checking with your doctor. Ask your health care professional for ways to lessen these effects.

Swallow the tablets whole with a drink of water. You can take the tablets with or without food.

If you vomit shortly after taking a dose of tamoxifen, check with your doctor. You will be told whether to take the dose again or to wait until the next scheduled dose.

Dosing—

The dose of tamoxifen will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of tamoxifen. If your dose is different, do not change it unless your doctor tells you to do so.

• For oral dosage form (tablets)
  • For breast cancer in women or men:
    • Adults—20 to 40 milligrams (mg) daily.
  • For reducing the risk of developing breast cancer in high-risk women:
    • Adults—20 milligrams (mg) a day, for five years
  • For reducing the risk of developing invasive breast cancer in women with ductal carcinoma in situ:
    • Adults—20 milligrams (mg) a day, for five years

Missed dose—

If you miss a dose of this medicine, do not take the missed dose at all and do not double the next one. Instead, go back to your regular dosing schedule and check with your doctor.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

It is very important that your doctor check your progress at regular visits to make sure that this medicine is working properly and to check for unwanted effects.

A woman should contact her healthcare profession right away if she develops:

• Changes in vaginal discharge or
• Changes in vision or
• Coughing up blood or
• Leg swelling or tenderness or
• Menstrual irregularities or
• New breast lumps or
• Pelvic pain or pressure or
• Sudden chest pain or
• Unexplained shortness of breath or
• Vaginal bleeding

If you seek medical attention for any reason, be sure to tell your healthcare professional that you take tamoxifen or have taken tamoxifen.

For women: Tamoxifen may make you more fertile. It is best to use some type of birth control while you are taking it. However, do not use oral contraceptives (“the Pill”) since they may change the effects of tamoxifen. Tell your doctor right away if you think you have become pregnant while taking this medicine.

Along with its needed effects, a medicine may cause some unwanted effects. Some side effects will have signs or symptoms that you can see or feel. Your doctor will watch for others by doing certain tests.

Also, because of the way this medicine acts on the body, there is a chance that it might cause other unwanted effects that may not occur until months or years after the medicine is used. Tamoxifen increases the chance of cancer of the uterus (womb) in some women taking it. Tamoxifen may cause blockages to form in a vein, lung, or brain. In women, tamoxifen may cause cancer or other problems of the uterus (womb). It also causes liver cancer in rats. In addition, tamoxifen has been reported to cause cataracts and other eye problems. Discuss these possible effects with your doctor.

Check with your doctor as soon as possible if any of the following side effects occur:

• For both females and males
  • Less common or rare
    • Anxiety;  blistering, peeling, or loosening of skin and mucous membranes;  blurred vision;  chest pain;  confusion;  cough;  dizziness;  fainting;  fast heartbeat;  lightheadedness;  pain or swelling in legs;  shortness of breath or trouble breathing;  weakness or sleepiness;  yellow eyes or skin 
    
    

• For females only
  • Less common or rare
    • Change in vaginal discharge;  chills ;  fever;  hoarseness;  lower back or side pain;  pain or feeling of pressure in pelvis;  pain, redness, or swelling in your arm or leg;  painful or difficult urination ;  rapid shallow breathing;  skin rash or itching over the entire body;  sweating ;  vaginal bleeding;  wheezing  
    
    

• For females and males
  • Frequency not determined
    • Bloating;  constipation;  darkened urine;  diarrhea;  difficult breathing;  indigestion;  itching;  joint or muscle pain;  large, hard skin blisters;  large hive-like swelling on face, eyelids, lips, tongue, throat, hands, legs, feet, and sex organs;  loss of appetite;  nausea;  pain in stomach or side, possibly radiating to the back;  red, irritated eyes;  red skin lesions, often with a purple center;  sore throat;  sores, ulcers or white spots in mouth or on lips;  unusual tiredness or weakness;  vomiting 
    
    

This medicine may also cause the following side effect that your doctor will watch for:

• For both females and males
  • Less common or rare
    • Cataracts in the eyes or other eye problems;  liver problems 
    
    

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

• For both females and males
  • Less common
    • Bone pain;  headache;  nausea and/or vomiting (mild);  skin rash or dryness  
    
    

• For females only
  • More common
    • Absent, missed, or irregular periods;  confusion;  decrease in amount of urine;  feeling of warmth redness of the face, neck, arms and occasionally, upper chest;  lower back or side pain;  menstrual changes;  nausea;  noisy, rattling breathing;  painful or difficult urination;  rapid, shallow breathing;  skin changes;  stopping of menstrual bleeding;  swelling of fingers, hands, feet, or lower legs;  troubled breathing at rest;  vaginal bleeding;  weight gain;  weight loss;  white or brownish vaginal discharge  
    
    
  • Less common or rare
    • Abdominal cramps;  black, tarry stools ;  bleeding gums;  blood in urine or stools;  Bluish color changes in skin color ;  discouragement;  feeling sad or empty;  irritability;  itching in genital area;  lack of appetite;  loss of interest or pleasure;  pain;  pinpoint red spots on skin;  stomach or pelvic discomfort, aching or heaviness;  swelling ;  trouble concentrating;  trouble sleeping;  unusual bleeding or bruising 
    
    

• For males only
  • Less common
    • decreased interest in sexual intercourse;  inability to have or keep an erection;  loss in sexual ability, desire, drive, or performance 
    
    

This medicine may infrequently cause hair thinning or partial loss of hair.

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.

Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although these uses are not included in product labeling, tamoxifen is used in certain patients with the following medical conditions:

• Malignant melanoma (a certain type of skin cancer)
• Cancer of the endometrium (lining of the uterus)

Other than the above information, there is no additional information relating to proper use, precautions, or side effects for these uses.