Effectiveness of Emergency Contraceptive Pills Taken After 72 Hours

Questions about contraception?

The efficacy of emergency contraceptive pills (ECPs) taken within three days after unprotected intercourse is approximately 75-89%.
If taken within 72 hours, the effectiveness is highest, but it decreases over time.
After three days, the effectiveness drops significantly, and ECPs are generally not recommended for use beyond five days, as their efficacy is much lower, and alternative methods of contraception should be considered.

Kanon, 10~19 year old female. Ask Date: 2015/07/08

Dr. Zhang Kunmin reply Obstetrics and Gynecology

Hello, the effectiveness of emergency contraceptive pills taken within three days is approximately 97%.
The effectiveness decreases over time, with studies in Canada showing around 90% effectiveness when taken between 3 to 5 days.
There is currently no data on effectiveness beyond this timeframe, and human trials cannot be conducted.
Thank you! Wishing you peace and health, Dr.
Zhang.

Reply Date: 2015/07/08

More Info

Emergency contraceptive pills (ECPs) are a critical option for preventing unintended pregnancies after unprotected intercourse or contraceptive failure, such as a broken condom. The effectiveness of these pills, including those containing ulipristal acetate (like Ella) and levonorgestrel (like Plan B), varies depending on when they are taken relative to the time of unprotected intercourse.

When taken within 72 hours (3 days) after unprotected sex, ECPs can significantly reduce the risk of pregnancy. For instance, studies indicate that ulipristal acetate can be effective up to 120 hours (5 days) after unprotected intercourse, with its efficacy remaining relatively high during this period. Specifically, the effectiveness of ulipristal acetate is approximately 98% when taken within 24 hours, and it decreases gradually but remains effective up to 120 hours, with an estimated efficacy of around 90% at the 72-hour mark.

However, the effectiveness of ECPs diminishes the longer you wait to take them after unprotected intercourse. After 72 hours, the data becomes less clear, and while ulipristal acetate may still provide some level of protection, it is not as reliable as when taken earlier. There is limited data on the effectiveness of ECPs taken beyond 120 hours, and it is generally recommended to consult a healthcare provider for further options if more than 5 days have passed since unprotected intercourse.

In terms of side effects, ECPs can cause various reactions, including nausea, fatigue, headache, and changes in menstrual cycles. These side effects are typically mild and resolve on their own. If a woman experiences severe side effects or if her menstrual period is delayed by more than a week after taking the pill, it is advisable to take a pregnancy test and consult a healthcare provider.

In summary, while ECPs are a valuable option for preventing pregnancy after unprotected intercourse, their effectiveness is highest when taken as soon as possible. For ulipristal acetate, taking it within 120 hours is recommended, but the sooner it is taken, the better the chances of preventing pregnancy. If more than 120 hours have passed, other contraceptive options should be discussed with a healthcare provider.

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