Jordan asked
Does the morning after pill work after 72 hours?
At a glance
- Effectiveness of the 'Morning After Pill' (i.e. levonorgestrel) decreases if taken more than 72 hours (3 days) after unprotected sex. Studies show that it retains some effectiveness after 72 hours but, by day 5, the risk of pregnancy significantly increases. Simply put, the sooner you take it, the better it will work. There are alternative options available if it has been more than 72 hours.
- The morning after pill [levonorgestrel] is most effective when taken as soon as possible after unprotected sex. Efficacy decreases significantly after 72 hours.
Answer
The 'Morning After Pill', also known as an emergency contraceptive pill, contains a high dose of the progestin levonorgestrel.
It may still work if you take it more than 72 hours after unprotected sex, but is not nearly as effective in preventing unplanned pregnancy as compared to taking it within 72 hours.
- Within 24 hours, it is nearly 95% effective.
- Within 72 hours, it is 87-90% effective.
- By 96 hours (4 days), it is 72-87% effective.
- By 120 hours, the risk of pregnancy increases nearly 5 fold when compared to taking within 24 hours.
As levonorgestrel works primarily by inhibiting ovulation (i.e. release of an egg), it certainly makes sense that the sooner you take it, the better.
Emergency contraceptives containing levonorgestrel are indicated (i.e. approved) by the FDA to be taken within 72 hours of unprotected sex. If it has been more than 72 hours, you do have other options (as discussed below).
Studies
One study evaluated the difference in the effectiveness of the morning-after pill in regard to administration time. They looked at administration within 72 hours and administration between 72-120 hours after unprotected sex.
The study found:
- An effectiveness rate of 87-90% in preventing pregnancy in those who took levonorgestrel (i.e. the morning after pill) within 72 hours of unprotected sex.
- For those who took it between 72-120 hours after unprotected sex, the effectiveness was decreased to 72-87%.
The study concluded:
What Is The 'Morning After Pill'?
The 'Morning After Pill' refers to a high dose of progestin (levonorgestrel) intended to decrease the chance of unplanned pregnancy after unprotected sex.
It is available in a variety of brand and generic products including:
- Plan B One-Step
- Next Choice One Day
- My Way
- Take Action
- Levonorgestrel
Inhibition or delay of ovulation is the primary mechanism of action of levonorgestrel emergency contraceptives. Studies also suggest it may affect fertilization, embryo transport, or implantation as secondary mechanisms.
It is important to take levonorgestrel emergency contraception as soon as possible within the 72 hours following unprotected intercourse for maximum effectiveness.
If vomiting occurs within 2 hours after taking a dose of the medication, your doctor may recommend repeating your dose.
The most common adverse reactions associated with levonorgestrel include:
- Nausea (13% to 23%)
- Vomiting (5.6%)
- Abdominal pain (13% to 18%)
- Fatigue (13% to 17%)
- Dizziness (9% to 11%).
- Menstrual changes [heavier (13% to 30%) or lighter bleeding (13%)]
- Breast tenderness (8% to 11%)
References
- Effectiveness of emergency contraceptive pills between 72 and 120 hours after unprotected sexual intercourse. PubMed
- Effect on pregnancy rates of the delay in the administration of levonorgestrel for emergency contraception: a combined analysis of four WHO trials. PubMed
- Ella Prescribing Information. AccessFDA
- Copper IUD As Emergency Contraception. Princeton.edu
