Those two types of medication are a type of birth control that uses hormonal therapy to disrupt the creation of an ovum, and to make sure the that if it does happen that an ovum is created it is unable to latch the endometrium of the uterus. However... While greatly affective hormonal treatment actually doesn't mean that it is 100 percent effective. There is a minor chance you could still get pregnant. The best way to avoid pregnancy is via not participating in intercourse ie, abstinence.