Tamoxifen must not be given during pregnancy. There have been a small number of reports of spontaneous abortions, birth defects and foetal deaths after women have taken tamoxifen although no causal relationship has been established.
Reproductive toxicology studies in rats, rabbits and monkeys have shown no teratogenic potential.
In rodent models of foetal reproductive tract development, tamoxifen was associated with changes similar to those caused by oestradiol, ethinyloestradiol, clomiphene and diethylstilboestrol (DES). Although the clinical relevance of these changes is unknown, some of them, especially vaginal adenosis, are similar to those seen in young women who were exposed to DES in utero and who have a 1 in 1000 risk of developing clear-cell carcinoma of the vagina or cervix.
Before starting treatment pregnancy has to be excluded. Contraceptive measures have to be taken at least up to 3 months after the end of therapy. The contraceptive "Pill" is not indicated. Before starting the therapy weaning is recommended.
It is not known whether tamoxifen is distributed into breast milk. Breast feeding is not recommended during tamoxifen therapy.