How effective is the morning after pill?

No contraceptive method works in 100% of all cases, but the morning after pill is 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 Levonelle online from our online doctor service and get it delivered the next day.

Key takeaways

  • The sooner you take the morning after pill, the more likely it is to be effective.

  • The morning after pill is less effective than most regular methods of contraception and should only be used in emergencies.

Contents of this article

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Which pill should I take - Levonelle or 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.

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

The alternative is ellaOne, 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.

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.

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, the effectiveness of emergency contraceptive pills might 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.

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 medication 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.

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 are very effective in protecting against unwanted pregnancies, they are less effective than preventative methods of contraception (such as the condom 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 GUM 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 from our trusted online doctor service and get it delivered.

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Order the morning after pill

There are three morning after pills - Generic Levonelle, Levonelle and EllaOne. Generic Levonelle and Levonelle need to be taken within 3 days of unprotected sex, whereas EllaOne can be taken until 5 days after sex. The sooner you take the morning after pill, the more likely it is to be effective. 

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