This article will answer the following commonly asked questions:

How Effective is the Morning After Pill in preventing pregnancy after unprotected sex?

Do Different Pills have Different Effectiveness?

When Should I Not Take The Morning After Pill?

How Effective Is The Morning After Pill? 

This is a difficult question to answer statistically, as the reason the morning after pill is taken is to prevent unplanned pregnancy. It’s very difficult to know for certain how many pregnancies were avoided due to the pill. The effectiveness of the morning after pill can also be determined by which brand you take and most crucially, how soon after unprotected sex the pill is taken. If taken within 24 hours of unprotected sex, it is thought that Levonelle will prevent pregnancy in over 95% of cases.

Another crucial point to note is that if you have already ovulated, the morning after pill will not be able to work effectively to prevent unplanned pregnancy. Information in this article relates to those who take it without having ovulated in that particular menstrual cycle.

In this article, we’ll explore the effectiveness of the two most widely used morning after pills available in the UK. If you’re worried about contraception failure, you can get EllaOne or Levonelle from our online doctor service and have it delivered the next day. 

Visit our online morning after pill clinic for treatments

Do Different Pills Have Different Levels of Effectiveness?

EllaOne is a morning after pill which is effective for up to 120 hours following unprotected sex. It contains the active ingredient ulipristal acetate. Levonelle is the most commonly prescribed emergency contraceptive pill in the UK. It contains the active ingredient levonorgestrel, which is a synthetic version of the hormone progesterone. In contrast with ellaOne, it has a tighter timescale for use of 72 hours, or 3 days, after unprotected intercourse.

Levonelle or Ellaone?

As stated, ellaOne is effective over a more extended period than Levonelle, but in the first twelve hours, their effectiveness is the same. Experts state that ellaOne is up to 95% effective when taken in the first 48 and 120 hours following unprotected sex and the success rate stays stable over the 120 hour period. In contrast, Levonelle’s effectiveness decreases over the period in which it can be taken. It is more effective the sooner you take it.

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


View Levonelle online from £3.99 

View ellaONE online from £23.50

More detailed information on the pills can be found at the following links:

These rates of effectiveness, however, can be affected by certain other factors which will be detailed further in this article.

How Does The Morning After Pill Work?

The morning after pill works to delay ovulation. Ovulation may either be stopped completely, or delayed long enough so that sperm is unable to fertilise the egg released.

What Factors Can Decrease the Effectiveness of the morning after pill?

Vomiting or Diarrhoea

Both EllaOne and Levonelle list nausea and vomiting as common side effects. If you have vomiting or diarrhoea within the first few hours of taking either pill, consult your doctor immediately. There is a risk it may not have had time to absorb if you vomit within two hours of taking the tablet. You may need a repeat dose to prevent pregnancy if this has happened to you.

Drug Interactions and the morning after pill

The morning after pill can interact with certain medications for other conditions which can make either one less effective or completely ineffective. If you are being treated for any of the following, speak to your GP or Pharmacist about your options before taking the morning after pill:

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

Health Conditions and the morning after pill

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 allergies to any of the listed ingredients.

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

High BMI

Although the link is not clinically proven, there is evidence to suggest that certain morning after pills are not as effective at preventing pregnancy in women with a high BMI. In some cases, where the BMI is severely high, a doctor might suggest an IUD (Intrauterine device) instead. If you’re concerned about a high BMI, consult your GP about suitable options for your weight range, as many women with high BMI’s have effectively used the morning after pill with success.

What If I Suspect I Might Be Pregnant?

It’s important to remember that the morning after pill will not prevent all pregnancies and therefore you are still at a slight risk of pregnancy. Some of the side effects of the morning after pill are similar to pregnancy symptoms such as spotting, abdominal pain and nausea/vomiting. If you have taken the morning after pill but remain concerned you may be pregnant, ensure you see your GP or local GUM clinic.  Unprotected sex greatly increases your risk of contracting certain STI’s which can be highly risky for a pregnant woman and foetus, so it’s important you are checked. It will also be important to ensure that the morning after pill hasn’t affected your pregnancy in any way.