Emergency Contraception with Plan B

Timing and Administration

The optimal timing for Plan B administration is within 72 hours (3 days) of unprotected intercourse, but it can still be effective when taken up to 120 hours afterward, as recommended by the Centers for Disease Control and Prevention (CDC) 1, 2
Plan B should be taken as soon as possible after unprotected intercourse to maximize effectiveness, according to the CDC 1
Treatment initiated within 72 hours reduces pregnancy risk by at least 75%, as stated by the CDC 3, 4
If using the two-dose regimen, both doses can be taken at the same time without decreasing efficacy or increasing side effects, as recommended by the CDC 5, 6

Effectiveness decreases as time passes after unprotected intercourse, as noted by the CDC 2
Pregnancy rates are low when Plan B is administered within 4 days but increase at 4-5 days after unprotected intercourse, according to the CDC 2
Plan B may be less effective in women with higher body weight, though it should still be offered, as stated by the CDC 7

Any regular contraceptive method can be started immediately after using Plan B, as recommended by the CDC 8
If vomiting occurs within 3 hours of taking Plan B, another dose should be taken as soon as possible, according to the CDC 8, 7

An advance supply of Plan B may be provided so it will be available when needed and can be taken as soon as possible after unprotected intercourse, as recommended by the CDC 1, 2
Studies show that advance provision increases use of emergency contraception but does not adversely affect regular contraceptive behavior, according to the CDC 2

Levonorgestrel causes less nausea and vomiting than combined estrogen-progestin emergency contraception pills, as noted by the CDC 8
Routine use of antiemetics before taking Plan B is not recommended, but pretreatment may be considered based on clinical judgment, as stated by the CDC 8