How Effective is Emergency Contraception?
Effectiveness and time limits of the morning after pill and IUD
In most cases, you need to use emergency contraception within 5 days of unprotected sex
The IUD (intrauterine device; copper coil) is the most effective method of emergency contraception
EllaOne is the most effective morning after pill
No method of contraception works 100% of the time. When it does not work, using an emergency contraceptive can be a very good way to stop an unwanted pregnancy. Emergency contraception should never be used in place of regular contraception.
There are 2 main types of emergency contraception: the morning after pill and the IUD (intrauterine device; copper coil). The morning after pill is one tablet that you take as soon as possible after unprotected sex. The IUD is a plastic, T-shaped device fitted into the womb by a doctor or nurse.
It’s hard to say exactly how effective each method is, but the IUD is generally thought to be the most effective (>99.9% effective), followed by EllaOne morning after pill (98-99% effective), and then Levonelle morning after pill (97-99% effective). Both types of morning after pill are only effective if taken before ovulation.
Morning after pill
What are the different types of morning after pill?
There are two main types of morning after pill available in the UK. They are:
- EllaOne: active ingredient ulipristal acetate
- Levonelle: active ingredient levonorgestrel (also available as generic Levonelle)
Levonelle is the most commonly prescribed emergency contraceptive pill. It goes by the name of Plan B in the US and Canada.
If you’ve had unprotected sex, you can take:
- Levonelle within 3 days (72 hours) of having unprotected sex
- EllaOne within 5 days (120 hours) of having unprotected sex
Which morning after pill is the most effective?
Studies have shown that:
- Levonelle gets less effective the longer you wait to take it after you’ve had unprotected sex
- EllaOne is more effective for longer as it is effective for up to 5 days (120 hours) after you’ve had unprotected sex
- EellaOne is more effective than Levonelle
What can make the morning after pill less effective?
The morning after pill can make you feel sick (nausea) and be sick (vomit). If you are sick or have diarrhoea within 3 hours, before your body has absored the active ingredients of the pill, it will not work. If this happens, you must talk to your doctor as you may need to take another dose.
High body mass index (BMI) - this can lead to emergency contraceptive pills being less effective, according to some studies.
- Both EllaOne and the copper coil are more effective than Levonelle at preventing pregnancy among women with a BMI of more than 26 or weight more than 70kg. Alternatively your doctor may suggest taking a double dose of Levonelle
- Having a BMI over 30kg or weight over 85kg can also make EllaOne less effective (a double dose of EllaOne is never recommended)
- An IUD is more effective than emergency contraceptive pills for women with high BMI
Other medication – the morning after pill should not be used if you’re also taking:
- St John's Wort
- HIV drugs such as ritonavir, or immune system suppressants
- drugs for tuberculosis like rifabutin
- barbiturates and other medication for preventing fits (seizures)
- certain antifungal medicines
- certain weight loss medications
- proton pump inhibitors like omeprazole (EllaOne only)
Tell your doctor or pharmacist about any other medications you’re currently taking or have used in the last month, before using a morning after pill.
Other health problems – the morning after pill is not suitable for anyone who has:
- severe liver problems
- stomach problems like Crohn's disease
- certain allergies or hormone problems
- Severe asthma treated with oral steroids (EllaOne only)
Regular contraception – if you’ve taken a contraceptive pill in the last 7 days or use any contraception that contains hormones, like the implant or the injection, it can make EllaOne less effective, but Levonelle will not be affected. If you’re taking the pill and use EllaOne, you should not restart your regular contraceptive pill for 5 days. You will also need to use condoms until your regular contraception is effective again.
If you’ve had unprotected sex, the most effective way of preventing pregnancy is to have an IUD fitted by a doctor or nurse.
You can use an IUD as emergency contraception up to 5 days after ovulation has occurred. Once it’s inserted, you do not have to have the IUD taken out as it can be left in place and used as your regular contraception.
Dr Simran Deo Doctor
Dr Simran Deo qualified from St George’s, University of London in medicine in 2006 with a distinction in her written finals. She went on to specialise in general practice, obtaining the MRCGP certification in 2012. In 2014 she received a merit for the Diploma in Dermatology from Cardiff University.Meet our doctors
Last reviewed: 11 Jun 2020
Levonelle 1500 microgram tablet (2018) EMC [accessed 9 July 2020]
Clinical Guideline: Emergency Contraception (March 2017, amended December 2017) FRSH [accessed 9 July 2020]
EllaOne patient information leaflet (2017) EMC [accessed 9 July 2020]
CEU Guidance: Drug Interactions with Hormonal Contraception (January 2017, last reviewed 2019) FSRH [accessed 9 July 2020]
You might need emergency contraception if you’ve recently had unprotected sex and want to reduce your risk of getting pregnant. Zava offers a morning after pill service, which includes a variety of options.