How Does Emergency Birth Control Work?

Many of us will choose to use the morning after pill (such as Plan B) or another type of emergency birth control in our fertile lifetimes. While it may be small in size, emergency contraception comes with a large and tricky history and our access to it remains a political issue today. Let’s unpack the backstory of emergency contraception, delve into the mechanics of the medicine and answer the question ‘how does emergency birth control work?’ Read on to learn more…

Illustration of an emergency birth control pill and a copper coil on a pink background

What is emergency contraception?

Emergency contraception can be used to prevent pregnancy after sex has taken place, including after unprotected sex or failure of another method (for example, a split condom). Emergency birth control should be used as soon as possible after unprotected sex, but can in some cases work up to 5 days after. 

What are the types of emergency birth control?

There are two types of emergency contraception. The morning after pill, also known as Plan B, and the copper coil or IUD. The morning after pill is taken orally and can be purchased at a pharmacy or obtained from a doctor or gynecologist. The copper IUD requires fitting in the uterus by a healthcare professional, but is also a long-acting contraceptive method which will continue to offer protection after it has been fitted.

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What’s the history of emergency birth control?

Our reproductive rights have always been a controversial topic. We won’t go into the full history of birth control rights – but our access to the morning after pill hasn’t always been open – for some women using it today it can still be considered very taboo and not everyone will be able to obtain it easily, if at all. Emergency birth control has only really been with us in recent history. Plan B was approved for use in the United States in 1999 and the morning after pill has been available over the counter in the United Kingdom since 2001.

Unfortunately, there’s still a degree of stigma which surrounds emergency contraception. Even the name Plan B brings to mind a sudden change of direction, of our first option not going as expected, it literally means resorting to second best. In fact, some sources suggest that the morning after pill was never originally intended to be an emergency contraception. However, launching at a time when the backdrop to birth control was very much a political one, there was controversy in a contraceptive which could be taken after intercourse. And this is still the case today. In fact, the morning after pill does not work as an abortive as some may think.

So, how does emergency birth control work?

Before going any further it’s important to note that just like all other methods of birth control, emergency contraception is not 100% effective. There is still a chance of getting pregnant even when we take the morning after pill or are fitted for an IUD. That said, taking emergency contraception can significantly reduce the risk of becoming pregnant – particularly in the case of the copper coil. 

It’s best to take the morning after pill up to three days after unprotected sex, but sooner is better. Emergency contraceptives use synthetic hormones just like birth control pills – in most cases a specific form of synthetic progesterone called Levonorgestrel. Most morning after pills work mainly by delaying ovulation (the release of an egg from the ovaries), meaning if ovulation has already happened, the morning after pill may not work. This is one of the reasons why it’s best to take it as soon as possible after intercourse. 

The copper IUD is a more effective form of birth control and works by stopping the sperm from fertilizing the egg, but it can also prevent implantation (a fertilized egg attaching in the uterus). IUDs have a very high effectiveness (>99.9%) and can be used for up to 10 years to prevent pregnancy. They require fitting and removal by a healthcare professional.

How do you know if the morning after pill worked?

It depends on where you are in your cycle as to how long you’ll have to wait to find out whether or not you are pregnant. Irregularities in any cycle are common. However, if you have taken emergency contraception and your period is late, there’s a chance you may be pregnant. There are some sensitive pregnancy tests which may be able to tell you if you are pregnant as soon as your period is late. However, if the test is negative and your period is a week late, it’s a good idea to take another test. It’s worth keeping in mind that stress and a change in hormones can also shift the regularity of our cycles. 

What are the side effects of emergency birth control?

In some cases there will be little or no side effects to taking the morning after pill. It is always worth discussing with your doctor if you are taking other medications or have existing health conditions. You may notice a change in your menstrual cycle such as spotting or lighter/heavier periods than usual. Other physical symptoms can include:

  • Feeling nauseous (consult a healthcare professional if you vomit soon after taking the morning after pill)
  • Stomach pain
  • Headache
  • Breast tenderness

If you choose the copper coil as a method of contraception, you may experience period cramps, as well as:

  • Pain/discomfort when the IUD is fitted
  • Spotting between periods
  • Irregular periods
  • Heavier/longer periods

Taking the morning after pill and using Natural Cycles

We have created the first and only birth control app which uses basal body temperature data paired with an algorithm which can work out your fertility and let you know which days you are at risk of getting pregnant in your cycle – we call these red days.

If you’re using Natural Cycles and have unprotected sex on a red day, or the barrier method fails, you can log using emergency birth control directly in the app. The algorithm can then adapt to the changes in your cycle. Used perfectly (this means no unprotected sex on red days), Natural Cycles is 98% effective, with typical use Natural Cycles is 93% effective. Natural Cycles has no known side effects and is 100% hormone-free. 

Discover Natural Cycles today

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Written By

Jennifer Gray

A writer with a passion for women’s health, Jennifer Gray has years of experience writing about various reproductive health topics including birth control, planning pregnancy, women’s anatomy, and so much more.

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Scientifically Reviewed

Jack Pearson

With 10 years of experience working in the field of fertility, Jack Pearson is Natural Cycles’ in-house expert. As Medical Affairs Manager, he dedicates his time to conducting groundbreaking research and educating healthcare professionals.