How does the emergency contraceptive pill work?

When you find yourself in need of emergency contraception, you want to know you’re making the best choice for your health - but with different options available, it can feel stressful to make that decision in the moment.

That’s why we’ve provided this guide to help you learn more about emergency contraception. Here, we outline the three types of emergency contraception available, how they work, and how effective they are at preventing unplanned pregnancies. Keep reading to learn more.

What is the emergency contraceptive pill?

Emergency contraception is used after unprotected sex or when regular contraception may have failed. It’s intended for occasional use and should be accessed as soon as possible after sex.

Some types of emergency contraception available in the UK come in the form of pills or tablets, and can be accessed from pharmacies. These are:

● Levonorgestrel emergency contraceptive pill

This type of emergency contraceptive pill is often known by brand names such as Levonelle. It’s usually taken as a single tablet. Whether it’s suitable for you can depend on factors such as when unprotected sex happened, your medical history, your weight and any other medicines you take.

● Ulipristal acetate emergency contraceptive pill

This type is often known by the brand name ellaOne. It’s also usually taken as a single tablet. As with levonorgestrel, suitability can depend on timing, health factors and current medicines, so it’s important to get advice from a pharmacist consultation.

If you’d prefer not to take a pill, there’s also the option of a copper intrauterine device - also called the copper coil or copper IUD. This is fitted into the womb by a trained healthcare professional - not available at most pharmacies - and can also provide ongoing contraception afterwards.

How does emergency contraception work?

All types of emergency contraception work to prevent pregnancy, but they do so in slightly different ways.

● Levonorgestrel

Levonorgestrel is a synthetic version of progesterone, a hormone involved in the menstrual cycle. It works mainly by delaying or stopping ovulation, which is when an egg is released from the ovary.

This matters because sperm can survive in the body for several days after sex. Even if you weren’t ovulating at the time, you can get pregnant when an egg is released afterwards, if the sperm survives long enough.

Levonorgestrel acts before ovulation happens. It helps to disrupt the hormonal signals that lead to the release of an egg, so there’s nothing for the sperm to fertilise. Timing plays an important role in how levonorgestrel works, which is why it’s important to seek advice sooner rather than later.

● Ulipristal acetate

Ulipristal acetate works in a slightly different way, affecting how the body responds to progesterone rather than artificially elevating progesterone levels.

In simple terms, ulipristal acetate blocks progesterone receptors so your body thinks the progesterone levels are lower than they really are. This causes ovulation to be delayed, reducing the risk of sperm and an egg meeting in the reproductive tract.

One key difference between this and levonorgestrel is that ulipristal acetate can act later in the ovulation process. Because of this, it may be the better choice depending on your circumstances.

● Copper IUD

The copper IUD is a small, T-shaped device which is inserted into the womb by a healthcare professional. It releases copper, which changes the environment in the womb and fallopian tubes.

Copper affects sperm movement and function, making it much harder for sperm to reach and fertilise an egg. If fertilisation does happen, the copper IUD may also help to prevent implantation in the womb.

Is the emergency contraceptive pill effective?

Levonorgestrel and ulipristal acetate are both effective emergency contraceptive pills, but timing matters - in fact, emergency contraception is usually more effective the sooner it’s used after unprotected sex.

Levonorgestrel is generally considered to be most effective in the first 12 hours. It is roughly:

● 95% effective when taken less than 24 hours after unprotected sex
● 85% effective within between 25 and 48 hours (two days)
● 58% effective between 49 and 72 hours.

After 72 hours (three days), levonorgestrel is less effective and isn’t typically recommended.

Ulipristal acetate can be taken up to 5 days after unprotected sex and is around 98% effective. Since it’s the most effective tablet option and can be taken later, it may be recommended more often than levonorgestrel.

The copper IUD is the most effective emergency contraception option and can be used up to 5 days after unprotected sex, helping to prevent unwanted pregnancy over 99.9% of the time. However, copper coils continue to provide protection until they’re removed, so they might not be the best choice if you’re not looking for long-term contraception.

Emergency contraception isn’t one-size-fits-all, and different options may suit different circumstances, timings and individual needs. The most important thing is to seek advice as soon as possible so a pharmacist can help you to choose the most suitable option for you.

References

https://cks.nice.org.uk/topics/contraception-emergency/background-information/efficacy/ 
https://www.nhs.uk/contraception/emergency-contraception/ 
https://www.nhs.uk/contraception/methods-of-contraception/iud-coil/what-is-it/ 
https://tht.org.uk/sexual-health/improving-your-sexual-health/contraception/emergency 
https://bnf.nice.org.uk/treatment-summaries/emergency-contraception/ 
https://bnf.nice.org.uk/drugs/ulipristal-acetate/ 
https://www.medicines.org.uk/emc/files/pil.8859.pdf 
https://bnf.nice.org.uk/drugs/levonorgestrel/