Tamoxifen During Pregnancy & Breastfeeding

by on April 24, 2012


The side effects of Tamoxifen can be extremely dangerous to an unborn child. Women who are pregnant or plan to become pregnant should discuss other treatment options with their doctor.  It is generally recommended that women of childbearing age begin their Tamoxifen prescription just after the start of their menstrual cycle. Your doctor may also request a pregnancy test before writing the prescription. Both men and women who are taking Tamoxifen should use reliable contraception to prevent pregnancy. Breastfeeding while taking Tamoxifen is discouraged.

According to the Food and Drug Administration, Tamoxifen belongs to Pregnancy Category D, meaning that it has been shown to cause harm to the unborn fetus, even in small doses. The following information will help pregnant and nursing mothers make the best decisions for themselves and their babies.

Tamoxifen during Pregnancy

Women who are pregnant, think they are pregnant or plan to become pregnant should avoid using Tamoxifen due to the increased risk of harm to the unborn child. This includes fetotoxicity—a process by which the fetus is poisoned by the medication, lower incidence of implantation—meaning that women may experience undue difficulty becoming pregnant, and low birth weight. The manufacturer of the drug also reported instances of spontaneous abortion, stillbirths and even major birth defects associated with Tamoxifen.

Tamoxifen should only be used during pregnancy when the benefits of the drug clearly and significantly outweigh the risks to the unborn child.

Understanding Pregnancy Symptoms on Tamoxifen

Since Tamoxifen is designed to restrict the production of certain hormones within the body, the signs and symptoms of pregnancy may present differently in patients who are using this medication. Fatigue, nausea and irregularities in the menstrual cycle are often the first signs of pregnancy, but changes in the natural hormones in a woman’s body can cause these same symptoms. Fortunately, women can rely on their basal body temperatures and a combination of the aforementioned symptoms to alert them to pregnancy. The use of Tamoxifen will not cause a spike in basal temperature; this is something that is only noticeable during pregnancy, especially when accompanied by other symptoms.

Tamoxifen and Breastfeeding

There have not been many studies to confirm the amount of Tamoxifen that passes into breast milk; this is because the medication is known to halt the production of milk and prevent engorgement of the breasts when administered no later than two hours post-delivery. There are no side effects reported with using the medication to treat engorgement in women who do not plan to breastfeed. Women who are taking Tamoxifen may notice that they are unable to breastfeed since the stimulation of the breast will no longer trigger the release of breast milk. Despite the lack of studies, the maker of the drug suggests that it be avoided by nursing women due to the potential for serious adverse effects to the baby.

Consulting a Physician

Women who are pregnant or who think they may be pregnant should immediately contact their physicians if they are taking Tamoxifen. This way, the decision can be made as to whether or not it is safer to continue the medication or stop taking the medication to favor the health of the fetus. Women who are taking the drug to treat or prevent breast cancer have likely already discussed the potential risks to themselves and the unborn if they were to become pregnant, though follow-up visits to discuss pregnancy prevention may be necessary. Always discuss these birth control methods with the physician who prescribed the Tamoxifen in order to ensure that there are no adverse interactions between the two.

Women should avoid taking Tamoxifen during pregnancy due to the serious risk of harm to the fetus; women who are pregnant or who think they are pregnant should seek immediate medical care. There are very few studies about the use of Tamoxifen and breastfeeding, but the manufacturer states it should be avoided as well.