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 help to prevent pregnancy soon after sex. Research suggests that while it’s recommended that EC is taken within 72 hours, it’s moderately effective up to 120 hours, 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 some options on the market, both over-the-counter and by prescription, to protect against unintended pregnancy for those that had 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). These forms of EC are most effective if started with 72 hours (three days) after sex, but are moderately effective up to 120 hours (five days after sex). If started within 72 hours of unprotected sex, progestin-only EC is more effective than combined hormonal EC that contain estrogen and progestin. Users are also less likely to have nausea and vomiting from taking progestin-only EC than from the combined regimen. The most common form of EC contains progestin as its only hormonal ingredient. Both brand name and generic versions 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.

A newer EC is ella, which is available by prescription. This ulipristal acetate based pill is considered the most effective on the market because it’s as effective immediately after sex as it is 120 hours (five days) after sex. Since ella requires a prescription, speaking with a health care provider about having it on-hand may be helpful so if needed, it can be taken as soon as possible.

It's typical for some people to have irregular periods or unexpected bleeding after using EC. However, if you’ve taken EC and don’t get your period within three weeks, you may want to visit 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 can help you figure out the best option for you. Because it's critical to take EC as soon as possible after sex, having options available over-the-counter means it can be picked up before it’s needed. Hormonal EC isn't intended to be used as a regular form of birth control. If EC is needed more regularly, other birth control and contraceptive options may be more effective. The copper intrauterine device (IUD) is another EC option; in addition to being used as EC, it can be used as long-term birth control. Additionally, emergency contraception (EC) isn't to be confused with the combination of pills, mifepristone and misoprostol, taken in a clinic setting by those who are already pregnant but wish to terminate the pregnancy (this is what’s referred to as a medical abortion).

Knowing that there are many options can provide a tremendous sense of security. If the 120 hour window was missed, a pregnancy test can be taken. If pregnant, a health care provider can discuss the options to help decide what 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 should you find yourself needing EC.


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