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Cancer Genetics

Pregnancy and Cancer Preventive Drugs

09/27/2000

Question:

Are there any studies regarding taking Tamoxifyn (sp?) and being pregnant. Family member will be taking it as a cancer preventive after some breast surgery and wonders about becoming pregnant.

Answer:

Tamoxifen works against estrogen. Therefore the most common side effects of taking tamoxifen are similar to menopause. Estrogen is necessary to conceive and maintain a pregnancy. Tamoxifen`s interference with estrogen causes infertility, may cause an abortion if taken in the early stages of pregnancy, and may cause birth defects in the baby. The effect of tamoxifen goes away after it is stopped; however, it is recommended that women wait at least two months after stopping the drug before trying to get pregnant.

There are many studies about the harmful effects of tamoxifen in pregnant rats. According to "Facts and Comparisons", January 2000 update:

"There are no adequate and well controlled studies in pregnant women. Spontaneous abortions, birth defects, fetal deaths, and vaginal bleeding have occurred. If this drug is used during pregnancy or if the patient becomes pregnant while taking this drug or within 2 months of discontinuing therapy, apprise her of the potential hazard to the fetus."

Women taking tamoxifen are advised not to become pregnant while taking tamoxifen and to use barrier contraceptive measures. They can not take birth control pills because of the interaction between tamoxifen and the hormones in the birth control pills.

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Response by:

Judith A Westman, MD Judith A Westman, MD
Associate Professor, Clinical Internal Medicine, Pediatrics and Medical Biochemistry
College of Medicine
The Ohio State University