It depends which type of birth control pill, and how soon after the beginning of your period you began the medication.
If you are on the “regular” combination pill, and you start the pills on your period (within 5 days of the start of your period), you are protected theoretically within 24 hrs. If you are on the “regular” combination pill, and you start the pills NOT on your period, you are protected after 7 days on the pill.
If you are on the progesterone only pills, you are protected 48 hrs after starting that pill. However, if you are 3 hrs late taking the progesterone only pill, then you need to use emergency contraception!
To be absolutely safe, waiting a month, would be best. And Dr. Sophia Yen (Pandia Health’s CEO & Co-Founder) always recommends using a condom to prevent Sexually Transmitted Infections and to avoid leaking sperm for the next 24 hrs. Ew!