Experts breakdown the need-to-know facts about emergency contraception effectiveness, timing, and side effects, plus offer guidance for moms when it comes to choosing the best option.

So, you and your partner weren't super careful. No worries—it happens, right? But a quick glance at the calendar sends a rush of gut-twisting fear straight through you as you realize you're way too close to your fertile window for this to be okay. 

Luckily, you can turn to emergency contraception to quell your fears. Depending on which particular form or brand you turn to, emergency contraception can reduce the chance of an unplanned pregnancy by as much as 85-99%, according to Courtney Benedict, Associate Director of Medical Standards Implementation at Planned Parenthood Federation of America. But just like birth control, not all emergency contraception options are created equal—nor are they all as easy to access as you may think. 

There are several types of emergency contraception to choose from, and it can be confusing to decipher the differences, especially when you're in a panic and under a tight timeframe. Here, experts explain the need-to-know facts about emergency contraception and offer guidance when it comes to choosing the best option so you can keep chaos at bay.

"Break Glass In Case of Emergency" box with pills inside
Credit: Illustration by Yeji Kim

What is Emergency Contraception?

Most commonly available in pill form, emergency contraception basically works like a super dose of birth control to reduce the risk of pregnancy. Depending on the option you choose, it can be used up to 3-5 days after you have unprotected sex. It's safe, and some types are easily obtainable at your local pharmacy. 

It's important to note that emergency contraception is not the same thing as an abortion pill. Using emergency contraception of any sort will not cause an existing pregnancy to end. It's simply a method of preventing pregnancy that differs from regular birth control options like the daily pill, a diaphragm, or using condoms. 

How Does Emergency Contraception Work?

When taken properly and within the recommended timeframe after sex, emergency contraception works primarily by delaying ovulation, says Benedict. Say, for instance, you had unprotected sex and you know you're on day 10 of your cycle. (Yikes.) That means based on a regular, 28-day cycle, you're pretty close to those peak fertile days (it's likely to be around day 14). Using an emergency contraceptive could potentially delay ovulation by a day or so, keeping you out of the danger zone of when you could possibly become pregnant. A copper IUD is also considered a form of emergency contraception—it works by preventing the sperm from reaching the egg. 

Emergency Contraceptive Options

Ella (Ulipristal) Emergency Contraceptive Pill

Ella is the only emergency contraception pill that contains ulipristal acetate, which is a "progesterone receptor modulator" according to the manufacturer’s website. It's considered the most effective morning after pill on the market, and if you're wondering does emergency contraception work during ovulation, Ella is the choice for you. According to their website,, "ella is the ONLY morning-after pill proven effective within the 24 hours around ovulation—when pregnancy risk is highest. This makes it the best option if you're close to ovulation."

Effectiveness: "Ella lowers your chances of getting pregnant by 85% if you take it within 5 days after unprotected sex," according to Heather Bartos, board-certified OBGYN and founder of Badass Women, Badass Health.

Biggest pro: Unlike other morning-after pills, ella doesn't become less effective as time passes after sex. Ella is also more effective than other morning-after pills for people who weigh 155 pounds or more. Ella delays or prevents ovulation even after your ovulation hormone (LH) has started to rise. 

Biggest con: Ella sounds like the best option out there, but we found it extremely difficult to obtain. "Ella requires a prescription, and not all pharmacies carry it. [And only] some states allow pharmacists to prescribe it," says Dr. Bartos. (Curious, we contacted eight different pharmacies in states across the country and none of them carried ella. However, it can be obtained online through the website which offers free next-day delivery, following a brief online medical consultation.)

Ella is the best emergency contraception option if:

  • You are ovulating or very close to ovulation
  • You are still within the 5-day timeframe after having unprotected sex
  • You are not breastfeeding. If you are breastfeeding, you'll have to "pump and dump" for 24 hours, says Dr. Bartos. Additional studies are required in order to determine the effects of ulipristal acetate on nursing babies. 

Plan B (Progestin-only) Emergency Contraceptive Pill

This emergency contraception pill is basically a large dose of progesterone. Like ella, it's a one-dose pill, but it differs in that as time passes, it becomes less effective. So it's best to take Plan B between 1 and 3 days after unprotected sex. 

According to Bartos, "Plan B is believed to act as an emergency contraceptive principally by preventing ovulation or fertilization (by altering tubal transport of sperm and/or ova). In addition, it may inhibit implantation (by altering the endometrium). It is not effective once the process of implantation has begun."

Effectiveness: “Plan B is up to 95% effective if taken within 24 hours after sex,” says Benedict. “But it loses its effectiveness if you are over 155 pounds and after 72 hours following unprotected sex.”

Biggest pro: Plan B is available over-the-counter without a prescription so it's a great option simply due to its widespread availability and reasonable cost.

Biggest con: In order to be effective, you must be sure to use it as soon as possible.

Plan B is the best emergency contraception option if:

  • You are within still within the 24–72 hour timeframe after having unprotected sex
  • You weigh less than 155 pounds

Copper IUD (Intrauterine Device)

The copper IUD used as emergency contraception primarily works by preventing fertilization of the egg by stopping the sperm and egg from meeting, says Benedict. It must be inserted within 5 days after unprotected sex, and works mainly by making sperm less able to fertilize the egg, according to the American College of Obstetrics and Gynecology (ACOG).

However, a word of caution: It's relatively uncommon to actually get it inserted on an emergency basis. "It depends on your provider's schedule AND your insurance. Some plans don't allow you to do the counseling and insertion on the same day, and it has to be inserted within 5 days of unprotected sex to work as emergency contraception," says Dr. Bartos. "So it's best to already have an OB-GYN as an established provider and ask to get in and have the IUD put in ASAP."

Effectiveness: If placed in time, an IUD is up to 99% effective at preventing pregnancy, says Dr. Bartos. 

Biggest pro: According to ACOG, it's the most effective method of emergency contraceptive for preventing pregnancy. Period.

Biggest con: Given that information, we're not entirely sure a copper IUD should even be considered a form of emergency contraception. Unless your OBGYN is super-speedy about ordering, fitting, and inserting the IUD (and none of the ones we called were), you could end up outside the window of effectiveness. Planned Parenthood clinics can also insert a copper IUD, but they, too, were unable to provide same-day service. 

An IUD is the best emergency contraception option if:

  • You are still within the 5-day timeframe after having unprotected sex
  • You already have an OB-GYN as an established provider and can ask to get in ASAP
  • Your insurance allows you to do IUD counseling and insertion on the same day
  • You don’t want to get pregnant anytime soon. Since the IUD can last anywhere from 10 to 12 years, it’s the best course of action if you don’t want to worry about another oops for a very long time. 

Emergency Contraception Side Effects

If you use emergency contraception, you may experience some side effects. The most common ones, as listed on the ACOG website, are: Headache, nausea and vomiting, breast tenderness, abdominal pain, dizziness, and fatigue. In most cases, these side effects should be mild to non-existent.

However, Dr. Bartos warns, "Plan B can definitely cause nausea—it's a sizable dose of progesterone. If you throw up less than 2 hours after taking it, it hasn't absorbed and you need to take again."