Aaron asked
How effective if I take Plan B on the 3rd day (56hr mark)?
Answer
The Plan B emergency contraceptive pill, containing levonorgestrel 1.5 mg, can be taken within 5 days (120 hours) after sexual intercourse and still be effective.
First, it is important to know that it is always best to take emergency contraception (i.e., the Plan B pill) as soon as possible after sex for maximum effectiveness. The pill is available over the counter and is sold at most pharmacies.
Some studies have indicated that emergency contraception pills are more effective when taken sooner after sex while other studies did not find the timing to be as important.
The package insert for Plan B recommends taking the pill within 3 days (72 hours) in order to be effective, based on the time-dependent studies.
However, because there was confusion about the timing of taking emergency contraception pills, the World Health Organization (WHO) conducted 4 trials to clarify this difference. After comparing results of the 4 WHO trials, it showed that there was no decline in efficacy until day 5. Per the study:
"For the four trials combined, odds ratios for pregnancy in the second, third and fourth day with respect to the first day were not significantly different [in regard to Plan B use]."
Plan B Effectiveness
Emergency contraception pills have been shown to reduce pregnancy rates by up to 79%, estimated based on the number of pregnancies that occurred when emergency contraception was not used, and work to delay the ovulation process.
While emergency contraception is safe and effective, taking other forms routine birth control pills (like combined oral contraception pills or what are often referred to as just “birth control pills”) are more effective than emergency contraception.
It is important to take an emergency contraception pill as soon as possible after sex but delaying up to no more than 120 hours will be as effective as taking it within the recommended 72 hours.
If you plan on continuing to have sex and do not want to get pregnant, talk to your doctor about routine birth control options as they are more effective than emergency contraception.
