Apri is a combination birth control pill that prevents pregnancy. The female sex hormones ethinyl estradiol and desogestrel prevent monthly ovulation from occurring. Apri also changes the cervical mucus and uterine lining, making it more difficult for sperm to reach the uterus and for a fertilized egg to attach. In order to effectively prevent pregnancy Apri should be taken once daily with no more than 24 hours between doses.