Please Explain: Birth Control

The earliest known female contraceptive device dates back to 1850 BC, when pessaries made of crocodile dung, honey, and sodium carbonate may have been the best option available to women. Chemical contraception has changed a lot since then. Today's Please Explain is about the chemistry of birth control. Dr. Rini Ratan is an OB/GYN with the Columbia Unversity Medical Center.