If you find yourself in a situation where you need to use the morning after pill, then it’s understandable to want reassurance that it’s going to work. In this blog, we look at how effective it is and the things you can do to prevent an unplanned pregnancy.  

What is emergency contraception? 

Emergency contraception is designed to stop you getting pregnant. If you have had unprotected sex or you think your usual method of contraception has failed, you have two options: 

copper IUD (intrauterine device) 

An IUD is a T-shaped piece of plastic with a copper coil that is effective at preventing pregnancy. It has to be fitted by a doctor or nurse, but it’s usually a quick process that can be undertaken in a local practice, just like a smear test. 

Once fitted, it works straight away and though you can have it taken out at any time, it usually lasts between five and ten years (depending on the type).  

emergency contraceptive pill 

There are two types of emergency contraceptive pills – Levonelle and ellaOne. Though they have different active ingredients, they work in a similar way, one of which is by delaying the release of an egg (ovulation) to prevent the sperm from making contact with it.

This method of contraception only works if it’s taken a short time after having unprotected sex, so exactly how effective is the morning after pill

How effective is the morning after pill? 

The IUD is the most effective form of emergency contraception – it works in over 99% of cases, but it’s the less invasive morning after pill that is used more often.  

Of the two emergency contraceptive pills, ellaOne is considered to be more effective than its rival Levonelle. According to a study for the NHS, only 1 to 2% of women who take ellaOne go on to become pregnant when they take it as prescribed¹

The morning after pill is so called because it is designed to be used after having unprotected sexual intercourse or failed contraceptive cover. The earlier you take it, the more effective it is, but the timings differ between the two types of emergency contraception.  

ellaOne contains ulipristal acetate which must be taken within 120 hours or five days of unprotected sex. It remains effective over the course of the five days, but you should still take it as soon as you possibly can for the best chance of success. 

Levonelle (levonorgestrel) must be taken within three days – or 72 hours – but its effectiveness diminishes the longer you leave it. It works in: 

  • Up to 95% of cases when it’s taken within 24 hours 
  • Up to 85% of cases when it’s taken within 25 to 48 hours 
  • Up to 58% of cases when it’s taken within 49 to 72 hours

To ensure maximum effectiveness, we recommend that you take the morning after pill as soon as you possibly can. But timing isn’t the only thing that can affect how well this type of emergency contraception performs – there are other things to look out for. 

Things to consider with the morning after pill 

There are certain medications that can affect how the morning after pill works, including: 

  • The herbal remedy, St John’s Wort 
  • Epilepsy, HIV or tuberculosis (TB) medicines 
  • Rifampicin and rifabutin (antibiotics)
  • Griseofulvin, a medicine used to treat fungal infections 

Your doctor or pharmacist will ask what you have taken in the last four weeks, so they can rule out the chances of any drug interactions that might stop the pill from working. 

Your body mass index, or BMI, may also play a factor in how well the emergency contraceptive pill works. Some experts think that it’s less likely to be effective if you have a high BMI – but that doesn’t mean it won’t work at all²

If you are sick within three hours of taking ellaOne or two hours of taking Levonelle, contact your GP for another dose (they may suggest that you have an IUD fitted as a precaution).  

What to do after you’ve taken the morning after pill  

You may not know whether the morning after pill has worked until your next period. If it’s lighter or shorter than normal, or you take the combined pill and you don’t get a withdrawal bleed, then speak to your GP (you may be asked to take a pregnancy test). 

Be aware that the morning after pill can affect hormonal contraceptives, including the:  

  • Combined pill 
  • Mini pill (progestogen-only pill)
  • Hormonal patch 
  • Vaginal ring 

When you come to restart your regular contraceptive, we recommend that you use a condom or a cap for up to 14 days after taking the emergency contraceptive pill. 

For help with family planning speak to your doctor or visit a sexual health clinic. You can prepare for unplanned emergencies by buying the morning after pill before you need it. 

This is particularly useful if you’re planning a holiday or a trip where you know you won’t be able to access emergency contraception. For the morning after pill to be effective, timing is critical, so the more prepared you are, the more likely it is to work. 

The key takeaway 

The copper IUD is the most effective form of emergency contraception, but the method most commonly prescribed is the morning after pill. 

The two types of branded pill, ellaOne and Levonelle, are both considered effective, but to prevent pregnancy they must be used correctly. Timing is key – the earlier you take the morning after pill, the more likely it is to work.

Although all of our content is written and reviewed by healthcare professionals, it should not be substituted for or used as medical advice. If you have any questions about your health, please speak to your doctor.

Authored Dec 01, 2021 by Joseph Issac, MPharm
Reviewed Dec 02, 2021 by Prabjeet Saundh, MPharm