How effective are expired birth control pills?

Like all medication, when it expires, it becomes less effective (and increases in its ineffectiveness as the time goes on). It's not easy to give a percentage as to how effective compared to non-expired pills, but if using expired Birth Control is your only option, I would use it with a condom or some other non-hormonal birth control to make sure you don't get pregnant. Otherwise, the likelihood of pregnancy will increase.