How Effective is the Morning After Pill?

Effectiveness and time constraints

Last reviewed: 23 Mar 2019

Girl sat in cafe investigating on her mobile how effective the morning after pill is

Key takeaways

  • ellaOne is the most effective morning after pill across 120 hours after unprotected sex

  • Levonelle is effective across 72 hours after unprotected sex but gets less effective the longer you wait to take it

  • The morning after pill may be less effective if you vomit after taking it, you have a high BMI, or your have existing health conditions or medications. Neither ellaOne or Levonelle are effective in preventing pregnancy if you have already ovulated

  • The morning after pill is only effective as an emergency contraceptive and should not be used too often - regular contraception is more effective

  • An alternative is the emergency IUD, also called the copper coil. It’s not a pill, but it’s the most effective emergency contraception

Contents of this article

No contraceptive method works in 100% of all cases, but the morning after pill can be very effective at preventing unwanted pregnancies if taken within certain time limits.

The effectiveness of the morning after pill varies depending on how soon after sex it is taken.

If you’ve had unprotected sex, you can buy ellaOne online from our online doctor service and get it delivered the next day.

Which pill should I take - Levonelle or ellaOne?

EllaOne is a morning after pill which works until up to 120 hours (5 days) after intercourse. Studies have shown that ellaOne is up to 95% effective when administered to women between 48 and 120 hours after unprotected sex.

EllaOne (ulipristal acetate) works over a much longer time period than Levonelle, but within the first 12 hours after sex, they are both as good as one another, so don't be discouraged if your doctor prescribes you Levonelle over ellaOne.

Levonelle is the most commonly prescribed emergency contraceptive pill in the UK (it goes by the name Plan B in the US and Canada). It must be taken within 72 hours (3 days) of sexual intercourse. It can also be bought as Generic Levonelle.

Levonelle is:

  • 95% effective if taken within 12 hours of unprotected sex
  • 85% effective if taken between 12- 24 hours of unprotected sex
  • 75% effective if taken between 24- 48 hours of unprotected sex
  • 58% effective if taken between 48- 72 hours of unprotected sex

After the first 12 hours, the effectiveness of Levonelle starts to decrease while ellaOne remains 95% effective until you pass the 120 hour mark. To put it into context, when you have unprotected sex, your average risk of pregnancy is around 1 in 20. With Levonelle, this risk falls to around 1 in 40, but with ellaOne, it is just 1 in 50.

Order the morning after pill online

from £20.00

from £34.00

from £13.00

No results found.

No results found.
Please check your spelling or try another treatment name.

Factors That Could Reduce The Morning After Pill's Effectiveness

Emergency contraceptives are not 100% effective and there are a number of factors that can either weaken or inhibit the drug's action. These are issues you must be aware of whenever you take the morning after pill.

Factor 1 -Vomiting

The morning after pill is known to cause both nausea and vomiting, which increases the risk of it failing. If you vomit before your body has absorbed the active substance of the pill, it won't work. If this happens to you, you must contact your doctor as you may need to take an additional dose.

If you vomit within 3 hours of taking either Levonelle or ellaOne the dose needs to be repeated.

Factor 2 - High Body Mass Index (BMI)

According to some studies, and the Faculty of Sexual and Reproductive Health (FSRH) the effectiveness of emergency contraceptive pills can be affected by a high body mass index (BMI).

  • ellaOne is more effective at preventing pregnancy amongst women with higher BMI's than Levonelle. Women with a high BMI may therefore be advised to use ellaOne rather than Levonelle.
  • Levonelle may be less effective if your BMI is over 26 kg/m2 or your weight is over 70kg. Having a BMI over 30kg/m2 or weight over 85kg can also make ellaOne less effective.
  • The copper IUD (a 'coil' fitted directly into the womb) is more effective than emergency contraceptive pills for women with very high BMI's.

Factor 3 - Other Medication

The morning after pill should not be taken in conjunction with the following medications:

  • St John's Wort
  • HIV drugs such as Ritonavir or immune system suppressants
  • TB drugs such as Rifabutin
  • Barbiturates and other seizure preventing medication

Tell your doctor or pharmacist about any other medications you are currently taking, before taking a morning after pill.

Factor 4 - Existing Health Complaints

The morning after pill is not suitable for:

  • Anyone with severe liver disease or those suffering from porphyria
  • Those with stomach problems such as Crohn's disease, or any other condition that affects how you process food and medications
  • Those with certain allergies or hormone problems

If any of the above applies to you, you should discuss alternative options with your health practitioner.

Factor 5 - Regular Contraception

Levonelle is not affected by regular contraception, but progestogens, which are part of regular contraceptive pills can make ellaOne less effective. This is why, after taking ellaOne you shouldn’t restart your regular contraceptive pill for 5 days.

Additional Risk Factors - It May Alter Your Periods

One of the major drawbacks of the emergency contraceptive pill, particularly when taken frequently, is that it may cause your periods to become irregular and unreliable. It can make your next period come up to a week late or early, make the bleeding heavier or lighter, depending on which time of your cycle you take the morning after pill.

Emergency Contraceptives Should Only Ever Be Used In An Emergency

Although emergency contraceptives can be very effective in protecting against unwanted pregnancies, they are less effective than preventative methods of contraception (such as condoms and the pill). The morning after pill should never be used as the main method of contraception.

Sometimes accidents happen and you may need to rely on emergency contraception. If you have recently had unprotected sex and need an emergency contraceptive pill, you are advised to visit your doctor, pharmacist or sexual health clinic without delay. The sooner you take the morning after pill, the more effective it will be. If you'd rather not see your GP about such matters, or if you're too busy to go to a clinic, you can order levonelle or ellaOne from our trusted online doctor service and get it delivered.


Dr Charlotte Hammerton studied medicine at the University of Nottingham and since graduating has worked in hospitals in London, Kent, and Sussex.

Meet our doctors

Last reviewed: 23 Mar 2019

Order the morning after pill
View Prices

Emergency Contraception

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.

Customer reviews
star full star full star full star full star full (1356)
star full star full star full star full star full by Bella, 14 Jun 2018
Such great service! Needed the parcel asap so next day delivery was important, and it came exactly on time. Thank you, will definitely use Zava again.
star full star full star full star full star full by Susan, 22 Mar 2019
Good customer service
star full star full star full star full star full by Val, 16 Aug 2018
I was impressed with the questionnaire to make sure the meds I requested were right for me and the follow up email from the prescribing doctor to see if I needed any support. The meds came promptly, were well packaged and are comfortably in date - I thought they might be very near their sell by date but I was wrong to be suspicious. If I ever need this service again I wouldn't hesitate.
star full star full star full star full star full by Mari, 09 Feb 2019
Great company. Fill in a short health questionaire. All orders checked by Dr before issuing which is reassuring when a new customer. Payment is quick and easy. Delivery is fast and goods well packaged in a sturdy plain white box. Will recommend Zava
star full star full star full star full star full by Tatjana, 25 May 2018
Very good and fast service

gmc logo GPC logo

Authorised and regulated by