If you are on a medication that contains estrogen, such as birth control pills or any birth control that affects your hormones, your supply may be low. (mymilkybaby.com)
Certain medications are designed to disrupt the endocrine system, such as birth control pills and breast and prostate cancer drugs. (sciencedaily.com)
So don't rely on breastfeeding as a birth control method. (babycenter.com)