Tamoxifen and Pregnancy Safety Issues

Tamoxifen, Reproduction, and Pregnancy Risks

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Is it safe to use Tamoxifen during pregnancy or could it be dangerous?  Does Tamoxifen affect fertility?

Tamoxifen Dangers in Pregnancy

If you're reading these words it's likely that you, or someone you care about is taking Tamoxifen.  Congratulations on being a survivor!  That said, there are many things you should know if you are considering pregnancy while taking Tamoxifen.

Don't Mix Tamoxifen and Pregnancy

Tamoxifen can hurt fertilized eggs (embryos) so don't take it if you are already pregnant. Due to the relatively high frequency of congenital anomalies, Tamoxifen should never be taken during pregnancy.

If you think you have become pregnant, stop taking Tamoxifen and contact your doctor right away. In lab studies on pregnant animals, Tamoxifen has caused birth defects, miscarriage, and prevented fertilized eggs from attaching to the wall of the uterus.

Tamoxifen and Fertility

Upon learning that Tamoxifen and pregnancy don't mix, you're probably wondering about the future.  When you are finished taking Tamoxifen, will pregnancy be okay?  Thankfully, after a wash out period of a few months off of Tamoxifen, the risk of birth defects from Tamoxifen goes away.  In addition, studies tell us that Tamoxifen is not associated with an earlier age of menopause.  In other words, Tamoxifen is unlikely to accelerate the "normal" process of decreased fertility that comes with getting older.

Tamoxifen and Contraception

It's very important to use good non-hormonal forms of contraception while taking Tamoxifen.  Methods of contraception such as birth control pills, contain estrogen and progesterone which can fuel the growth of breast cancer, potentially increasing the risk of a recurrence.

  Many doctors recommend a combination of 2 methods of contraception just to be safe while taking Tamoxifen.  Talk to your doctor about the various methods of contraception.  Try condoms, spermicide, a diaphragm, or an IUD to prevent a pregnancy.  It may also be a good time to familiarize yourself with emergency contraception options - methods available if, for example, a condom breaks, to prevent pregnancy.  Since these, like oral contraceptives, contain female hormones, it's extremely important that you talk to your oncologist before using these.

Tamoxifen and Your Reproductive System

While chemotherapy may temporarily make you "menopausal," it's not uncommon for fertility to return even years after this treatment.  You won't suddenly become menopausal on Tamoxifen, unless you were already close to that point when you started treatment.  On the contrary, infertility specialists sometimes prescribe high doses of Tamoxifen to increase egg production.  Once the ovaries are in overdrive, Tamoxifen is stopped and then contraception can be attempted. 

Play It Safe for a Season

Using Tamoxifen after treatment for breast cancer reduces the risk of recurrence by up to 50%, and increases the chance that you will be around in the future to enjoy your family.

  It can be hard to put childbearing on hold during this time, but for now, it's important to focus on your own health and well-being.  If you're using Tamoxifen, it's also important to be aware that there are medications which can interact with its metabolism - essentially making it as if you weren't taking the drug at all.  Learn as much as you can in order to get the benefits you are sacrificing for. When you do really want to plan a pregnancy you should be off of Tamoxifen for at least 2 months.  This allows time for the drug to pass out of your system.

What If You Really Want a Baby Now?

If you want to become pregnant and feel that time is running out for your fertility, discuss your options with your doctor.

It may be possible to take Tamoxifen for less than five years and still get the benefit of this drug. Your doctor can review your diagnosis with you, and help you figure out the minimum amount of time you need to take it. Research has shown that pregnancy after breast cancer treatment does not significantly increase your chances of recurrence. Spend some time and effort recovering your health and think about your future priorities. There are many paths to parenthood, and one may be right for you.

If You're Just Starting Treatment

If you've recently been diagnosed, and before treatment, learn how cancer treatment can affect fertility, and what you can do to plan ahead.


Amant, F., Loibl, S., Neven, P., and K. Van Calsteren. Breast cancer in pregnancy. Lancet. 2012. 379(9815):570-9.

Braems, G., Denys, H., De Wever, O., Cocquyt, V., and R. Broecke. Use of tamoxifen before and after pregnancy. Oncologist. 2011. 16(11):1547-51.