Morning after pill

Dear Alice,

How long after having had sex is the taking of the morning after pill useful?

— Intrigued

Dear Intrigued, 

Also known as emergency contraception (EC), the "morning after pill" contains a high dose of hormones that helps to prevent pregnancy if taken soon after sex. Research suggests that while most EC has the highest effectiveness if taken within 72 hours, it’s moderately effective up to 120 hours later, dependent on the formula that’s used (more on that later!). Emergency contraception is often referred to as the "morning after pill," but the sun doesn’t have to come up for it to be taken. In fact, the general consensus is that for most formulations, the sooner it’s taken, the more effective it is. Currently, there are several options on the market, both over-the-counter and by prescription, to protect against unintended pregnancy for those who had their contraceptive method fail or had unprotected sex. 

Hormonal EC may work in several ways: by delaying or inhibiting release of an egg (ovulation), preventing the egg and the sperm from meeting (fertilization), or keeping a fertilized egg from attaching to the uterine wall (implantation). The most common form of hormonal EC contains levonorgestrel, which is a type of progestin (a hormone naturally occurring in your body and used in many forms of hormonal birth control). It’s recommended to take this type of EC within 72 hours (3 days) of sex, though taking it up to 120 hours (5 days) after sex is less effective but still better than nothing. All that said, the longer you wait, the less effective this type of EC is, so it’s recommended to take it as soon as possible. Both brand-name and generic versions of levonorgestrel EC are available on-the-shelf at many pharmacies and drugstores, and a prescription or proof-of-age isn’t needed in order to purchase them. 

Another type of morning-after pill is ella, a hormonal EC that contains ulipristal acetate. The different chemical compound makes ella more effective than other types of hormonal EC, but it does require a prescription. It’s highly effective if taken within five days after sex (compared to levonorgestrel’s three-day window), but like levonorgestrel, the sooner you take it, the more effective it is. Since ella requires a prescription, it may be challenging to get it within the recommended window of time after sex. You might consider speaking with a health care provider about getting a prescription in advance to ensure you have ready access if you ever need it in the future.  

Since both types of hormonal EC work by disrupting ovulation, it’s common to experience irregular periods or unexpected bleeding or spotting in the weeks after taking it. However, if you don’t get your period within three weeks of taking EC, there’s a chance that it didn’t work, so you may wish to take a pregnancy test or speak with a health care provider. Temporary side effects of using EC may include: 

  • Headache 
  • Dizziness 
  • Cramping and abdominal pain 
  • Breast tenderness 
  • Nausea or vomiting 

Talking with your health care provider may be helpful in determining which EC method is the best option for you. Once you’ve decided, you may wish to go ahead and pick up an extra pack in advance so you have it on-hand if you need it again in the future. However, hormonal EC isn't intended to be used as a regular form of birth control. If you find yourself regularly using EC to prevent pregnancy, it may be helpful to speak with a health care provider about other birth control and contraceptive options that may be more effective and better suit your needs. The copper intrauterine device (IUD) is one such choice; in addition to being a long-lasting birth control option, it’s also highly effective as EC if inserted within five days after sex. Additionally, some forms of regular hormonal birth control can be used as emergency contraception when taken in larger than usual quantities, but it’s not generally recommended to use this method if you have other EC options available to you. Using extra doses of birth control as emergency contraceptive is less effective than using levonorgestrel or ulipristal acetate, and it’s more likely to cause side effects such as nausea and vomiting. Prior to taking birth control as EC, it’s recommended to review which birth control brands can be used and their dosage requirements. Finally, emergency contraception (EC) isn't to be confused with the combination of pills used in a medical abortion; the former prevents a pregnancy from occurring while the latter are taken in a clinic setting by those who are already pregnant but wish to terminate the pregnancy. 

Knowing that there are many options for emergency contraception may provide a sense of security for some people, but EC is unfortunately not 100 percent effective. If the 120-hour window has passed, you may need to wait and see whether you get your period on-schedule, and if your period is late, a pregnancy test can be taken. If the test comes back positive, a health care provider can discuss the options to help you decide what you want to do next. 

Kudos to you for asking these questions! Having this information in advance can help ensure you know your options and what decisions may be most appropriate for you if you find yourself needing EC. 

Last updated Sep 10, 2021
Originally published Dec 21, 1995

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