Plan B (levonorgestrel emergency contraception) is most effective when taken as soon as possible after unprotected sex, ideally within 72 hours (3 days). Its effectiveness is up to about 89% if taken within this 72-hour window
. While it can be taken up to 5 days after unprotected sex, its effectiveness decreases the longer you wait
. The primary way Plan B works is by delaying ovulation, so it is less effective if ovulation has already occurred
. In summary:
- Plan B is FDA-approved for use within 72 hours (3 days) after unprotected sex
- It is up to 89% effective if taken within 72 hours, with the highest effectiveness when taken within 24 hours
- It can be taken up to 5 days after sex, but effectiveness declines over time
- Plan B works by delaying ovulation and will not terminate an existing pregnancy
Therefore, Plan B is effective primarily within 3 days but can still reduce pregnancy risk up to 5 days post-intercourse, with diminishing effectiveness the later it is taken.
