Birth control pills work by preventing the joining of the sperm and the egg. They can prevent ovulation from occurring and can thicken the cervical mucus, preventing the sperm from reaching the egg. There are two kinds of birth control pills: 1.) combined estrogen and progestin and 2.) progestin only. The combination pill is the most commonly prescribed. When used perfectly, the birth control pill is 99% effective. However, the pill must be taken at the same time every day, a challenge for many people. With typical use, the pill is 93% effective. In addition, the pill—like the IUD—does not protect against STIs, and therefore should be combined with a condom. Furthermore, certain prescription medications can lower the pill’s effectiveness. 
 

The pill has many uses beyond preventing contraception. It can reduce menstrual cramps, acne and cysts, lighten periods, and decrease chances of ectopic pregnancy and ovarian and endometrial cancers. The pill is used as a treatment for endometriosis, polycystic ovarian syndrome (PCOS), and premenstrual syndromes (PMS, PMDD). For these reasons, many people take the pill regardless of whether they are sexually active or attempting to prevent pregnancy.