how long taking a birth control pill before it becomes effective
2 doctors agreed: 7 days: Most doctors recommend 7 days of birth control pills before having unprotected intercourse. Even with pills, there is still a 4-6% chance of pregnancy over course of a year. If miss 1 pill, take that pill immediately the next day with that days pill. If miss 2 days pills, take 3 pills and use back up method until you get your period.