Tamoxifen

The Basics

What is Tamoxifen?

Used to treat breast cancer.

Brand names for Tamoxifen

Nolvadex

How Tamoxifen is classified

Antineoplastic Agents, Estrogen Antagonists

Tamoxifen During Pregnancy

Tamoxifen pregnancy category

Category DNote that the FDA has deprecated the use of pregnancy categories, so for some medications, this information isn’t available. We still think it’s useful to list historical info, however, given what a common proxy this has been in the past.

What we know about taking Tamoxifen while pregnant

NOLVADEX (tamoxifen citrate) may cause fetal harm when administered to a pregnant woman. Women should be advised not to become pregnant while taking NOLVADEX (tamoxifen citrate) or within 2 months of discontinuing NOLVADEX (tamoxifen citrate) and should use barrier or nonhormonal contraceptive measures if sexually active. Tamoxifen does not cause infertility, even in the presence of menstrual irregularity. Effects on reproductive functions are expected from the antiestrogenic properties of the drug. In reproductive studies in rats at dose levels equal to or below the human dose, nonteratogenic developmental skeletal changes were seen and were found reversible. In addition, in fertility studies in rats and in teratology studies in rabbits using doses at or below those used in humans, a lower incidence of embryo implantation and a higher incidence of fetal death or retarded in utero growth were observed, with slower learning behavior in some rat pups when compared to historical controls. Several pregnant marmosets were dosed with 10 mg/kg/day (about 2-fold the daily maximum recommended human dose on a mg/m² basis) during organogenesis or in the last half of pregnancy. No deformations were seen and, although the dose was high enough to terminate pregnancy in some animals, those that did maintain pregnancy showed no evidence of teratogenic malformations. In rodent models of fetal reproductive tract development, tamoxifen (at doses 0.002 to 2.4-fold the daily maximum recommended human dose on a mg/m² basis) caused changes in both sexes that are similar to those caused by estradiol, ethynylestradiol and diethylstilbestrol. Although

Taking Tamoxifen While Breastfeeding

What are recommendations for lactation if you're taking Tamoxifen?

Since tamoxifen can suppress postpartum lactation and its excretion into breastmilk is not known, it should be avoided in nursing mothers.

Maternal / infant drug levels

Since tamoxifen can suppress postpartum lactation and its excretion into breastmilk is not known, it should be avoided in nursing mothers.

Possible effects of Tamoxifen on milk supply

Tamoxifen was more effective than placebo in suppressing lactation and preventing engorgement and pain in two trials in postpartum mothers. Neither study stated what, if any, physical methods (e.g., breast binding) were used concurrently.[1][2] In one study of 80 women, tamoxifen 10 mg four times daily for 5 days was more effective than placebo in suppressing a rise in serum prolactin after use of a mechanical breast pump after 5 days of treatment, but not on day 3. All of the women in the study had breastfed a previous child.[2] The other study of 150 women used 2 regimens: tamoxifen 30 mg twice daily for 2 days followed by 10 mg twice daily for 2 days; and 10 mg twice daily for 14 days. More women in the tamoxifen groups had not previously breastfed an infant.[1]

In a case report, a woman with a history of breastfeeding 4 children (the last having been weaned 10 months earlier) began lactating after 1 week of a cancer chemotherapy regimen for breast cancer that included tamoxifen 20 mg/day. Milk production continued for several weeks until tamoxifen was discontinued after which it did not return during 12 more weeks of chemotherapy.[3]

Possible alternatives to Tamoxifen