Emergency Contraception Basics: Options and Timing

Emergency contraception is birth control used after sex to reduce the chance of pregnancy. People use it after a condom breaks or slips, after missed birth control pills, after sex without contraception, and after assault. It is a normal part of reproductive health care, and in the United States one form of it sits on the shelf at most pharmacies with no prescription and no age limit.

The two things that matter most are speed and choosing the right method for your situation. This page covers the options available in the US, how long you have, how effective each one is, and where to get them.

What is emergency contraception and how does it work?

Emergency contraception is a pill or an intrauterine device used within a few days after sex to prevent pregnancy from starting. The pills work mainly by delaying or preventing ovulation, the release of an egg from the ovary, so there is no egg available for sperm to fertilize.

Because the pills work by postponing ovulation, they are much less effective once ovulation has already happened. That is the central reason timing matters so much, and why a method that does not depend on ovulation timing, the copper IUD, is the most reliable choice.

The copper intrauterine device works differently. Copper is toxic to sperm and eggs, so it prevents fertilization, and it also makes the uterine lining inhospitable to implantation.

Does emergency contraception end a pregnancy?

No. Emergency contraception prevents pregnancy from starting; it does not end an established one. If you are already pregnant, emergency contraception will not affect the pregnancy, and the American College of Obstetricians and Gynecologists is clear on this point.

Medically, pregnancy begins at implantation, when a fertilized egg attaches to the lining of the uterus. Emergency contraception acts before that point, primarily by stopping an egg from being released at all.

Emergency contraception is also a different medicine from medication abortion. Medication abortion uses mifepristone and misoprostol to end an established pregnancy and requires medical involvement. The two are frequently confused, and the distinction is factual rather than a matter of opinion.

What are the emergency contraception options in the US?

Three main options: the levonorgestrel pill, available over the counter to anyone of any age with no prescription; ulipristal acetate, which requires a prescription; and the copper IUD, which a clinician must place and is the most effective of the three.

	Levonorgestrel pill	Ulipristal acetate	Copper IUD
Common names	Plan B One-Step and many generics	ella	Paragard
How you get it	Over the counter, on the shelf, no prescription and no age restriction	Prescription required	Placed by a clinician
Time window	Labeled for use within 72 hours; some effect up to 120 hours but clearly declining	Up to 120 hours (5 days)	Up to 120 hours (5 days) after sex
Effectiveness	Good if taken quickly; falls off with delay	Maintains effectiveness better across the full 5 days than levonorgestrel	The most effective option, well over 99 percent
Effect of body weight	Appears less effective at higher body weights	Also may be less effective at very high body weights, though less so than levonorgestrel	Not affected by body weight
Ongoing contraception	No	No	Yes, up to about 10 years if you keep it
Typical cost	Lowest, often around the price of a pharmacy purchase	Moderate, prescription needed	Highest up front, often covered by insurance

There is a fourth option worth knowing about. The CDC's 2024 U.S. Selected Practice Recommendations for Contraceptive Use also includes the levonorgestrel 52 mg IUD as an emergency contraception option. Like the copper IUD, it must be placed by a clinician and provides ongoing contraception afterward.

How soon do you need to take it?

As soon as you reasonably can. Every option works better the sooner it is used, and levonorgestrel in particular loses effectiveness noticeably with each passing day.

Time since sex	Best options
Within 24 hours	Any of the three. Levonorgestrel is the easiest to obtain immediately
24 to 72 hours	Ulipristal or a copper IUD if you can access them; levonorgestrel if not
72 to 120 hours	Copper IUD first, then ulipristal. Levonorgestrel is not labeled for this window
More than 120 hours	Contact a clinician. Emergency contraception is no longer expected to work; discuss testing and ongoing contraception

If you cannot get to a clinic or a prescription quickly, take the over-the-counter levonorgestrel pill now rather than waiting for a better option later. A method used today generally beats a more effective method used in two days.

One important interaction: do not take levonorgestrel and ulipristal together or within days of each other, because levonorgestrel can reduce how well ulipristal works.

Which option is the most effective?

The copper IUD, by a wide margin. Placed within 5 days, it is more than 99 percent effective at preventing pregnancy, which is substantially better than either pill, and its effectiveness does not depend on where you are in your cycle or on your body weight.

Among the pills, ulipristal generally outperforms levonorgestrel, and the gap widens later in the 5-day window. Levonorgestrel is the least effective of the three but also the fastest to obtain, and speed is a real advantage.

Certain medicines reduce how well the pills work, including some seizure medicines, rifampin, some HIV medicines and the herbal supplement St. John's wort. If you take any of these, a copper IUD is the better choice, so tell the prescriber or clinician what you are taking.

Does body weight affect emergency contraception?

Yes, for the pills. Levonorgestrel appears to be less effective at higher body weights, and ulipristal may also lose some effectiveness at very high body weights, though less markedly. This is not a reason to avoid taking a pill if that is what you can access.

If you weigh more than roughly 165 pounds, or have a BMI over about 30, the copper IUD is the option least affected by weight and is worth pursuing if you can get an appointment within the 5-day window. Where a pill is the only realistic option, take it, because a reduced chance of working is better than none.

Taking a double dose of levonorgestrel is sometimes suggested online. That is not an established recommendation, and it is a question for a clinician or pharmacist rather than a forum.

Where can you get emergency contraception?

Levonorgestrel pills are sold over the counter in pharmacies, supermarkets and online across the US, with no prescription and no age restriction. They are stocked on the shelf rather than behind the counter, so you should not have to ask anyone for them.

Ulipristal (ella) needs a prescription. You can get one from your primary care provider, a gynecologist, a family planning clinic, an urgent care center, or a telehealth service, several of which can send a prescription to a local pharmacy the same day.

The copper or levonorgestrel IUD needs an appointment with a clinician. Family planning and community health clinics, gynecology offices and some urgent care centers place them. When you call, say clearly that you need it for emergency contraception and give the date of the sex, because that usually gets you triaged faster.

Cost varies. Insurance often covers prescription and clinic-placed options, generic levonorgestrel is generally cheaper than brand-name versions, and many clinics offer sliding-scale fees. If you have been sexually assaulted, emergency departments and many clinics can provide emergency contraception, and support services are available whether or not you choose to report.

What side effects should you expect?

The pills are generally well tolerated. The most common effects are nausea, tiredness, headache, dizziness, breast tenderness, mild abdominal cramping, and a next period that comes earlier or later than usual.

If you vomit within about 2 to 3 hours of taking a pill, contact a pharmacist or clinician, because the dose may not have been absorbed and you may need to repeat it. IUD placement commonly causes cramping and spotting for a few days, and copper IUDs can make periods heavier or crampier for the first several months.

What emergency contraception does not do is affect your future fertility. There is no evidence that using it, including using it more than once, causes lasting harm to your ability to become pregnant later.

What should you do afterward?

Three things: plan ongoing contraception, think about STI testing, and take a pregnancy test if your period is late.

• Ongoing contraception. Emergency contraception is less effective than regular methods and is not designed for routine use. After levonorgestrel you can start or restart hormonal contraception right away, using a backup method such as condoms for 7 days. After ulipristal, wait 5 days before starting hormonal contraception, and use backup until then, because starting sooner can reduce how well the ulipristal works.
• STI testing. Emergency contraception does not protect against sexually transmitted infections. If there is any chance of exposure, ask about testing. If there is a possible HIV exposure, post-exposure prophylaxis must be started within 72 hours, so contact a clinician or emergency department immediately rather than waiting.
• Pregnancy test. Take one if your period is more than about a week late, or if it is much lighter or shorter than normal. Emergency contraception reduces the chance of pregnancy but does not remove it.

When should you see a doctor?

Seek urgent care immediately for severe or one-sided lower abdominal pain, shoulder tip pain, dizziness or fainting in the weeks after taking emergency contraception. Those can indicate an ectopic pregnancy, where a pregnancy implants outside the uterus, which is a medical emergency.

Contact a clinician if you have a positive pregnancy test, if your period has not arrived a week after it was due, if you vomited within 3 hours of the pill, if you have very heavy bleeding, or if you have fever, worsening pelvic pain or unusual discharge after IUD placement.

Also reach out if you find yourself using emergency contraception often. That is a signal that a regular method would serve you better, not a judgment, and a family planning clinic can walk you through the options without any moralizing.