Emergency Contraception: What It Is and How It Works
Emergency contraception can lower the chance of pregnancy after unprotected sex or after a birth control method fails, for example if a condom breaks or you miss pills. It is not meant to be used as regular birth control. The sooner you use it, the better it usually works.
This article explains the options, how fast you need to act, who it may work less well for, and what to expect afterward. If you want to choose a regular method, see Birth Control Options Explained: How They Work and How to Choose.
Medical Disclaimer
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The information here is general in nature and is not a substitute for personalized medical advice from your own doctor or qualified healthcare provider, who can take your full medical history and individual circumstances into account. Always consult your doctor or another qualified healthcare provider with any questions you may have regarding a medical condition, and never disregard professional medical advice or delay seeking it because of something you read on this site.
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Quick Answer
There are two kinds of emergency contraception: pills and the copper IUD. According to the NHS, the levonorgestrel pill can be taken within 3 days (72 hours) after sex, and the ulipristal pill and the copper IUD within 5 days (120 hours) (1). The copper IUD is the most effective option, but it needs a clinic visit, so pills are often quicker to get. Whichever you choose, act as soon as possible.
Your Options
The Levonorgestrel Pill
This pill is sold under names such as Plan B One-Step in the U.S. and Levonelle in the UK. It should be taken within 3 days (72 hours) after unprotected sex. In many places you can buy it at a pharmacy without a prescription. The sooner you take it, the better it works.
The Ulipristal Pill
This pill is sold as ella in the U.S. and ellaOne in the UK. It can be taken within 5 days (120 hours) after unprotected sex. Depending on where you live, you may need a prescription.
If you want to start hormonal birth control afterward, wait at least 5 days before you begin it. Until your next period, use a condom or another barrier method.
The Copper IUD
The copper IUD is a small device that a doctor or nurse places in the uterus within 5 days (120 hours) after unprotected sex. It is the most effective form of emergency contraception. It can then stay in place as regular birth control for up to 10 years (4), or you can have it removed later.
An IUD cannot be placed at home. A trained doctor or nurse must fit it (1), and appointments can be hard to get at short notice. Call a clinic as soon as you can and say that you need emergency contraception. If you cannot be seen within 5 days, take a pill instead, and do not wait.
How Emergency Contraception Works
According to the Office on Women’s Health, emergency contraceptive pills work mostly by preventing or delaying ovulation (2). They may also stop fertilization if ovulation has already happened. They are different from the abortion pill, and if you are already pregnant they do not stop or harm the pregnancy (2).
Because the pills mainly work by delaying ovulation, timing matters. This is why you should not wait. The earlier you use emergency contraception, the more time there is before an egg is released.
Body Weight and Medicines That Can Matter
The CDC notes that emergency contraceptive pills may be less effective in people with a body mass index of 30 or higher (3). Limited data suggest a higher pregnancy risk in this group. The pills are still safe to use, but the copper IUD is not affected by weight and may be a better choice (3). Ask a pharmacist or doctor which option is best for you.
Some medicines can also make the pills work less well, including rifampin, carbamazepine, and efavirenz (3). Tell the pharmacist or doctor about every medicine you take. Weight-loss surgery that affects how the body absorbs food can reduce how well pills work, so an IUD may suit you better (3).
Emergency contraception can be used more than once, and the CDC lists repeated use as safe (3). It is still not a good regular method, because other methods work better. It is also fine to use while breastfeeding.
What to Expect Afterward
Side effects of the pills are usually mild and short-lived. They can include:
- Headache
- Belly pain
- Tiredness
- Dizziness
- Nausea
- Breast pain
Your next period may come early or late, and you may have some spotting. Take a pregnancy test if your period is more than a week late, or sooner if you think you might be pregnant. See Why Is My Period Late? and Early Signs of Pregnancy: What You May Notice Before a Test for more. Ask your pharmacist what to do if you feel sick soon after taking the pill.
Emergency Contraception and Infections
Neither the pills nor the copper IUD protect against sexually transmitted infections, including HIV. Condoms lower the risk. If you think you may have been exposed to an infection, ask a clinic about testing, and about medicine that can prevent HIV.
Where to Get It
In many countries, levonorgestrel pills are sold in pharmacies. In the UK, the pill is free at most sexual health clinics and GP surgeries, and also at many pharmacies, and the copper IUD is fitted by a nurse or doctor. Rules and costs differ in other countries, so ask a pharmacist, a doctor, or your local sexual health service.
When to See a Doctor
Contact a healthcare professional if:
- Your period is more than a week late.
- You have severe or one-sided lower belly pain, especially with dizziness or fainting.
- You would like to start a regular birth control method.
- You think you may have been exposed to a sexually transmitted infection.
- You are taking other medicines and are not sure the pill will work.
Severe or one-sided belly pain after emergency contraception can be a sign of an ectopic pregnancy. This is rare, but it needs urgent medical care, so do not wait to see if it passes.
Conclusion
Emergency contraception can prevent pregnancy after unprotected sex, and acting early gives it the best chance of working. The pills work for 3 to 5 days, depending on the type. The copper IUD is the most effective option, but it needs a clinic visit, so call as soon as you can.
Body weight and some medicines can change which choice is best. It does not protect against infections, and it is not a regular method. If you would like a method that suits you every day, talk to a doctor, nurse, or midwife about your options.
Sources
- NHS. Emergency Contraception.
- Office on Women’s Health (U.S. Department of Health and Human Services). Emergency Contraception.
- Centers for Disease Control and Prevention (CDC). U.S. Medical Eligibility Criteria for Contraceptive Use: Classifications for Emergency Contraception.
- Centers for Disease Control and Prevention (CDC). About Contraception.
