The hormonal birth control pill was first marketed in the United States in the 1960s, and it had a profound impact on the world. Birth control pills allow women to engage in sexual activity at any time during their menstrual cycle without fear of pregnancy, and essentially work by tricking the woman's body into thinking that it is already pregnant with timed doses of estrogen. In addition to estrogen, birth control pills contain progesterone, another female hormone which has an influence on the reproductive system. When taken as directed, most birth control pills are over 90% effective.

The origins of birth control pills can be found in experiments on rabbits in the 1930s, when researchers discovered that high doses of progesterone prevented ovulation, meaning that no eggs would be present in the uterus to be fertilized by sperm. In the 1940s, scientists successfully synthesized both estrogen and progesterone, opening the way to the birth control pill, which was developed and tested in the 1950s. In 1960, the Food and Drug Administration approved the use of the pill for American women, and human sexuality and family planning have not been the same since.

The hormones in birth control pills combine to prevent the body from releasing an egg. Should an egg be released, the progesterone makes it difficult for the egg to travel down the fallopian tube, and also alters the uterine lining to prevent implantation in the unlikely event of fertilization. In addition, progesterone thickens cervical mucus, so that sperm have difficulty navigating. The combination of estrogen and progesterone make pregnancy a challenge, although it can happen.

Most pill users have noticed that their birth control pills are different colors, and must be taken in a specific order. This is because the dosages vary from week to week, with one week actually containing placebo pills with no hormones, to allow the body to slough the thickened uterine lining in a menstrual period. It is very important that birth control pills be taken at the same time every day, and in the proper order: never borrow a friend's pills, as they may not be the same as yours, and they will throw your cycle off, putting you at risk of pregnancy.

While birth control pills are excellent at preventing pregnancy, they do not prevent any sexually transmitted diseases (STDs). To provide STD protection and extra insurance against pregnancy, condoms should always be used during sexual activity. Proper combined use of a condom and birth control pills will greatly reduce the risk of pregnancy and prevent infection with a potentially incurable STD.