Tamoxifen and Fertility

You've just finished chemotherapy and are ready to get pregnant. Then your doctor says you should start tamoxifen. Tamoxifen is a hormonal therapy that lowers the risk of recurrence in women with hormone-receptor-positive breast cancer.

Does tamoxifen induce menopause?

Although it causes hot flashes, tamoxifen does not make you menopausal. About 20% of women will have irregular periods on tamoxifen, but only a few stop their cycles entirely.

Tamoxifen will not cause early menopause unless you're already on the brink. After you stop taking tamoxifen, your body usually goes back to where it was before.

Tamoxifen is sometimes used as a fertility treatment

Tamoxifen does not stop ovulation — it actually increases ovulation.  This is probably true even at the low daily doses that you take for breast cancer treatment.  At higher doses, tamoxifen is in fact used as a fertility treatment.

Infertility doctors sometimes use tamoxifen to stimulate the ovaries to produce more eggs in women who are trying to get pregnant.  However, in these circumstances, the woman's ovulation and fertilization status is being closely monitored by the infertility specialist.

Is it safe to take tamoxifen before or during pregnancy?

As a general rule, for women not under the care of an infertility specialist, tamoxifen should not be used if you are pregnant or trying to get pregnant.  Your doctor might give you a pregnancy test to be sure you're not pregnant when you begin tamoxifen treatment.

• Do not try to get pregnant while you're taking tamoxifen.  Tamoxifen may cause damage to developing embryos. Use an effective nonhormonal barrier form of birth control (such as condoms or a diaphragm along with spermicide) while taking tamoxifen as part of your breast cancer treatment.  Continue to use barrier methods of birth control for 2 months after you finish tamoxifen treatment, even if you don't have regular periods.  Don't plan on trying to get pregnant until at least 2 months after tamoxifen treatment is over. 
• If you're already pregnant, do not start taking tamoxifen.
• If you're taking tamoxifen and you think you've become pregnant, stop taking the tamoxifen and call your doctor immediately.

It may be confusing to hear that tamoxifen can be used as a fertility drug but that it's harmful to developing embryos. As a fertility treatment, tamoxifen is used to stimulate the ovaries to get more eggs ready for ovulation. At this point in the process, the eggs have not been fertilized yet. And tamoxifen does not damage unfertilized eggs. After the eggs are fertilized and become embryos, tamoxifen may have a harmful effect. But at that point fertility has already been achieved. So before you're pregnant, tamoxifen is considered safe. But once you're pregnant, it's not.

Weighing tamoxifen and pregnancy concerns

The first question to ask your doctor is, "How important is it for me to take tamoxifen to lower the risk of the cancer coming back?"

If you would benefit from taking tamoxifen, take it for at least the period of time that you are urged to wait to become pregnant. Two years of tamoxifen is better than none, and five years is better than two.

If you're in your mid-30s, you might decide to take a calculated risk: You could take tamoxifen for two years, then stop the tamoxifen and try to get pregnant.

Or, after careful consultation with your doctor, you may decide that tamoxifen offers you only marginal benefit — and you choose forgo it.

You also might decide to take tamoxifen the full recommended five years. Waiting those five years may put you past 40, reducing the possibility of having your own biological child. You could choose to adopt during that time. Later, if your periods come back, you could try to have a biological child.

If you have stored embryos from fertility treatment before chemotherapy, you may choose to take tamoxifen for the full five years, even it puts you into your 40s. This is because your age at the time the embryos are implanted is not nearly as crucial to a successful pregnancy as your age when the eggs were harvested.

Another option, if you don't want to wait for five years and if you have frozen embryos, is to consider the option of a gestational carrier, or surrogate. This is a woman you make a contract with to carry the baby for you.