Emergency Contraceptive Pills: Timing and Effectiveness Explained

Use of emergency contraceptive pills?

When purchasing emergency contraceptive pills, the pharmacy staff mentioned that taking them on the second day of menstruation is also acceptable.
Is the contraceptive effectiveness the same as taking them on the fifth day?

qm, 20~29 year old female. Ask Date: 2015/07/26

Dr. Zhang Kunmin reply Obstetrics and Gynecology

Hello, the effectiveness of emergency contraceptive pills is not related to the number of days after intercourse, but rather to the timing of ingestion after the event.
When taken within 72 hours after intercourse, the effectiveness is approximately 97%.
However, it is not 100%, and there is about a 3% failure rate.
Nonetheless, it is still considered a viable option for prevention.
Thank you! Wishing you peace and health, Dr.
Zhang.

Reply Date: 2015/07/26

More Info

Emergency contraceptive pills (ECPs) are designed to prevent pregnancy after unprotected intercourse or contraceptive failure. The timing of when these pills are taken is crucial for their effectiveness. There are two main types of emergency contraceptive pills: those containing levonorgestrel (Plan B One-Step and its generics) and those containing ulipristal acetate (ella).
Timing and Effectiveness:
1. Levonorgestrel (Plan B): This type of ECP is most effective when taken within 72 hours (3 days) after unprotected intercourse. However, it can still be taken up to 5 days after, but its effectiveness decreases significantly over time. The sooner it is taken, the better the chances of preventing pregnancy. Taking it on the second day after unprotected sex is much more effective than taking it on the fifth day.

2. Ulipristal Acetate (ella): This ECP can be taken up to 120 hours (5 days) after unprotected intercourse and maintains its effectiveness throughout this period. It is generally more effective than levonorgestrel, especially when taken later within the 5-day window.

Comparing Timing:
If you take the ECP on the second day after unprotected intercourse, you are likely to have a higher chance of preventing pregnancy compared to taking it on the fifth day. The effectiveness of levonorgestrel drops significantly after the 72-hour mark, while ulipristal acetate remains effective but may still be less effective than if taken earlier.

Mechanism of Action:
ECPs work primarily by delaying or inhibiting ovulation. If ovulation has already occurred, the effectiveness of ECPs is reduced. They do not terminate an existing pregnancy and are not effective if implantation has already taken place.

Considerations:
- Menstrual Cycle Timing: The timing of your menstrual cycle can influence the effectiveness of ECPs. If you are close to ovulation, the chances of preventing pregnancy may be lower, especially with levonorgestrel.

- Body Weight: Some studies suggest that ECPs may be less effective in individuals with a higher body mass index (BMI). If you are concerned about this, it may be worth discussing with a healthcare provider.

- Follow-Up: If your period is more than a week late after taking ECPs, it is advisable to take a pregnancy test and consult a healthcare provider.

Conclusion:
In summary, while taking emergency contraceptive pills on the second day after unprotected intercourse is more effective than taking them on the fifth day, the type of ECP matters. Levonorgestrel is less effective after 72 hours, while ulipristal acetate can be taken up to 120 hours with maintained effectiveness. Always consult with a healthcare provider for personalized advice and to discuss any concerns regarding emergency contraception.

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Hello, based on your method of consumption, there should still be about a 90% effectiveness in contraception. However, I would like to remind you that if your period is more than a week late, you should check for pregnancy. Thank you! Wishing you safety and health, Dr. Chang.

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