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Illustrations by Emma Günther

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When is emergency contraception most effective?

You can take the morning-after pill for up to 120 hours

Top things to know about emergency contraception:

  • The emergency contraceptive pill (morning-after pill) isn’t bad for you

  • IUDs are the most effective form of emergency contraception

  • Emergency contraceptive pills are most effective the sooner you take them, but can still have some effect for up to 4-5 days (96-120 hours) after unprotected sex

  • Emergency contraceptive pills might be far less effective, or ineffective, during roughly 1-2 days of each cycle, right around the time of ovulation

  • Even if you’re not sure if it will be effective, it may be better at preventing pregnancy than taking nothing

Emergency contraception (EC) offers people a chance to prevent an unwanted pregnancy. It can be used after you had unprotected vaginal sex, did not use your method of birth control correctly, or were sexually assaulted.

Download Clue to track your birth control

  • Download the Clue app on the App Store
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Most types of EC are less effective than other forms of modern birth control, and they don’t protect against sexually transmitted infections. But EC is an important tool when you need it. It can make you much less likely to get pregnant, depending on where you are in your cycle and what type of EC you choose.

There is a lot of confusion around the use and effectiveness of emergency contraception. If you are someone who may use emergency contraception in the future, tracking your cycle can help you make an informed decision about which emergency contraceptive to choose.

Emergency contraception should be used as soon as possible after unprotected sex, to help prevent pregnancy. Its effectiveness depends on when you ovulate.

The average cycle is 28 days long, and the average day of ovulation is day 14. You are most likely to get pregnant during the “biological fertile window” which is about 6 days long — from about 5 days before ovulation, until 24 hours after ovulation. But the timing of the biological fertile window can change from cycle to cycle and is highly variable even for those who perceive their cycle as “regular” (1, 2).

The Progestin pill is most likely to be effective if taken between days 9-12 of your cycle (3). The antiprogestin pill is most effective if taken between days 9-14 of your cycle (3). The IUD is effective throughout the cycle (3). These estimates are based on a predictable cycle, which isn’t the same for everyone.

Not sure about the difference between a period and a cycle? Read What is the menstrual cycle.

How do I know if emergency contraception will work?

It can take up to six years after someone first gets their period for cycles to settle into a predictable pattern  (4, 13). Stress, sleep changes, jet lag, and intensive exercise can also affect the timing of ovulation, usually delaying it (5-7). Ovulation is also affected by some medical conditions that influence reproductive hormones like polycystic ovarian syndrome (PCOS) (2). Tracking your period and knowing the days you are most at risk for pregnancy can be an effective method of better understanding your cycle and ovulation timing.  

If you are unsure if you are in the biological fertile window of your cycle, using an EC may be a good idea. Any method may be more effective than nothing (8). Some people may choose to keep an emergency contraceptive pill (an ECP) on hand for backup in emergencies, so they won’t lose time getting a pill if they ever need one quickly. ECPs can be bought in advance at many pharmacies, medical clinics, and online. Some require a prescription while others do not.

What are my emergency contraception options?

There are two options for emergency contraception in the USA: Emergency contraceptive pills (ECPs) and intrauterine devices (IUDs).

Making emergency birth control work for you

About half of all pregnancies in the USA are unintended (9-11).  The popularity of long-acting reversible contraception (LARC) methods like IUDs helps decrease this number (13, 14).  

Emergency contraception can stop an unintended pregnancy before it happens. An ECP is not a long-term solution for birth control — it isn’t as effective as other forms of birth control. But knowing the options can help make emergency contraception as effective as possible for you. Understanding your cycle and acting quickly are the most important things you can do to make emergency contraception work for you.

Where can I order emergency contraception online

NURX will ship Ella or New Day (generic Plan B) to your home.

Wisp will ship Plan B to your home or send a prescription for Ella to your preferred pharmacy.

Amazon Pharmacy has Plan B and other similar options available.

Using the Clue app to track your periods, ovulation date, and when you have sex can help you choose the right emergency contraception when you need it.  

Use custom tags to track contraceptive methods like emergency contraception.

This article was originally published April 13, 2016.

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