The length of time that it will take for your birth control pills to protect you will be determined by which type of oral contraceptive you take. After the initial waiting period, oral contraceptive can be 99% effective at preventing pregnancy when taken as directed and 91% effective with typical use.
How Long Does it Take a Progestin-Only Pill to Work?
Progestin-only pills work by thickening the cervical mucus, making it more difficult for sperm to reach the egg. It can also help to lessen the chance of ovulation. When prescribed a progestin-only pill, you will likely be instructed to take it within the first five days of the start of your cycle, which is typically on the first day of your period.
Unless you have a shorter cycle, 23 days or less, the pill will become effective immediately if you begin taking the pills within the correct time frame. If you do have a shortened cycle, it can take two full days for the pill to become effective at preventing pregnancy.
How Long Does it Take a Combination Pill to Work?
Combination pills contain both estrogen and progestin which work together to prevent ovulation from occurring. You should start your combination pill contraceptive on the Sunday following your period. It can take a full week for the pill to become effective, so a back-up contraceptive is recommended to ensure protection against pregnancy.