Tamoxifen has been used in the treatment of invasive breast cancer, as well as prevention of breast cancer for close to 40 years. After numerous research studies showed a connection between uterine cancer and tamoxifen, an increasing number of women are filing lawsuits against the drug’s manufacturer.

What is Tamoxifen?

Tamoxifen is a selective estrogen receptor modulator (SERM) that is often used to treat and reduce the risk of breast cancer. Since its approval in 1977, tamoxifen has been used by millions of women and men with advanced stages of breast cancer.

In the U.S., roughly one in eight women are at risk of developing breast cancer in their lifetime. It’s estimated that there will be more than 240,000 new cases of invasive breast cancer in 2016.

For patients who have been diagnosed with breast cancer, tamoxifen may be prescribed after surgery, radiation and chemotherapy. Tamoxifen is also commonly given to patients who have a high risk of developing breast cancer. Generally, these patients are at least 35 years of age or older and have a combination of factors that are associated with the development of breast cancer – medical condition, family history, etc.

While tamoxifen helps in the treatment of breast cancer, it has been known to cause serious side effects that can be life-threatening. Dangerous conditions – blood clots in the lungs or veins, stroke and uterus cancer – are rare, but it’s important to talk to your doctor about any symptoms you may experience.

How does Tamoxifen work?

Selective estrogen receptor modulators (SERMs), like tamoxifen, work by binding to estrogen receptors. In doing so, they block estrogen from binding in breast tissue which stops the growth of breast cancer cells.

The National Surgical Adjuvant Breast and Bowel Project (NSABP) conducted a study to determine how effective tamoxifen is in preventing breast cancer in high-risk women. Results showed a 50 percent decrease in both invasive and non-invasive breast cancer in women who were treated with tamoxifen. Other research that has been completed found that using tamoxifen for five to 10 years reduces the chance of breast cancer reoccurring or spreading to the other breast.

Tamoxifen is administered in a tablet form. The length of treatment, as well as dosage amount varies based on the patient’s medical condition and age. Typically, tamoxifen is taken daily for a minimum of five years, depending on your body’s response to the medication. Time in between doses may change based on the strength of tamoxifen that has been prescribed.


Tamoxifen Side Effects

Each year, millions of patients rely on tamoxifen as part of their breast cancer treatment. However, some individuals experience negative side effects after taking tamoxifen. Some symptoms are minor and may only last several days. If symptoms persist or get worse, you should seek medical assistance immediately.

Tamoxifen increases your risk of developing serious, life-threatening cancers such as liver cancer and uterine cancer. Regular gynecological exams can help detect the early signs of uterus cancer and prevent it from spreading further. Other dangerous conditions that have been linked to the use of tamoxifen include strokes, heart attacks, and blood clots in the heart or lungs. Unfortunately, it may take months or years for some side effects to appear, which can be extremely detrimental to your health.

Before taking tamoxifen, talk with your doctor about potential risks and complications to determine if this is the best form of treatment for you.

Common Side Effects

  • Menstrual changes
  • Weight gain or loss
  • Hot flashes
  • Swelling
  • Nausea
  • Vaginal discharge

Serious Side Effects

  • Endometrial and uterine cancers
  • Blood clots
  • Stroke
  • Chest pain or heart attack
  • Shortness of breath
  • Cataracts

Who is at Risk?

Tamoxifen Risk

The risk factors associated with taking tamoxifen are different for every patient. Serious side effects – uterine cancer, endometrial hyperplasia and endometrial proliferation – often depend on the amount of tamoxifen prescribed and the length of time taking the medication.

Research suggests that postmenopausal women taking tamoxifen have an increased risk of developing endometrial hyperplasia or cancer. These health conditions can be closely monitored with routine medical exams. While there is no known increased risk of uterine cancer in premenopausal women taking tamoxifen, patients should notify their physician if they experience any uncomfortable side effects.

Many medical professionals recommend that women with invasive forms of breast cancer should continue taking tamoxifen, as the benefits of overcoming breast cancer far outweigh the risks. However, the black box warning should be taken seriously, especially for women who are considering taking tamoxifen as a breast cancer prevention drug.

Talk with your doctor about the risks and potential complications of taking tamoxifen. Frequent medical evaluations can also help with identifying any risk factors before they become life-threatening.

Tamoxifen Black Box Warning

In 2002, the FDA issued a black box warning for tamoxifen. Black box warnings are the strictest type of FDA labels on the market.

Tamoxifen was required to carry a black box warning after research identified the risk of uterine sarcoma in patients. Information provided by the FDA states that women are eight to 17 times more at risk of developing uterine sarcoma taking tamoxifen than those not on the medication. Although uterine sarcoma is rare, it is often not discovered until it has aggressively spread and is more difficult to treat.

The black box warning on tamoxifen is meant to advise doctors and patients about its serious, potentially life-threatening side effects. If you experience any health complications while taking tamoxifen, notify your physician immediately.

Evidence of Tamoxifen Complications

Tamoxifen Complications

After first entering the market, Tamoxifen appeared to be promising for many breast cancer patients. However, harmful side effects related to the drug have been discovered over the years. Health complications linked to tamoxifen started to appear as early as the 1970s.

In 1978, a study was published in Cancer Treatment Reports about patients having retina damage and decreased vision due to tamoxifen. More information about long-term eye problems, like cataracts, was included in a 1992 Cancer Treatment Report. Several years later in 1996, research conducted by the International Agency for Research on Cancer determined that tamoxifen increases a woman’s risk of developing uterine cancer. This topic has continued to be studied over the past couple of decades.

Tamoxifen comes with benefits as well as risks. Discuss your medical history with your doctor to determine the right form of treatment for you.

Drug Reactions with Tamoxifen

Taking a new prescription, such as tamoxifen, can have various interactions with any current medications you are on. Make a list of drugs including prescription, over-the-counter and herbal remedies you are taking. Provide this information to your physician so they can check to see if any drugs cause harmful reactions when taken with tamoxifen.

Many drugs can cause adverse reactions when combined with tamoxifen

Some of the drugs include:

  • Adrenal gland disorder drugs
  • Blood thinners
  • Bromocriptine
  • Cancer-fighting drugs
  • Seizure drugs
  • Tuberculosis drugs

Learn About Resources for Tamoxifen Side Effects

If you or someone you care about has been affected by negative side effects from tamoxifen, learn more about financial resources and how you can pay for treatments.

Find Out More About Tamoxifen Resources Now

Sources & Author

Last Edited: October 31, 2017