How effective is the morning after pill?

Dr Kathryn Basford

Medically reviewed by

Dr Kathryn Basford

We offer 3 types of morning after pills to use as emergency hormonal contraception, EllaOne, Levonelle and levonorgestrel. All 3 of these pills are most effective against unplanned pregnancy if taken within the first 24 hours after you’ve had unprotected sex.

They work by preventing the release of an egg from your ovaries, also known as ovulation. They will not be effective if you have unprotected sex after ovulation, so your next option would be to have a copper intrauterine device (IUD) fitted. A copper IUD is the most effective form of emergency contraception.

EllaOne has been shown to be more effective than Levonelle or levonorgestrel and can be used for up to 120 hours after unprotected sex. If you are already using a hormonal method of contraception such as the contraceptive pill, the morning after pill may not be as effective. You may not be able to use morning after pills if you are taking certain long term medications.

EllaOne, Levonelle, and levonorgestrel are all available to buy over the counter from your local pharmacy after a short consultation with a pharmacist. You can also request these morning after pills from Asda Online Doctor.


EllaOne effectiveness

EllaOne contains the active ingredient ulipristal acetate. You can take EllaOne up to 120 hours (5 days) after having unprotected sex, but it’s best to take it as soon as possible.

EllaOne has been shown to be the more effective than Levonelle or generic levonorgestrel when taken within 120 hours of unprotected sex.

EllaOne can also delay ovulation, but it is not effective if you have already ovulated. It’s not always easy to predict when you are ovulating, so it’s best to take EllaOne as soon as possible if you’ve had unprotected sex.

If you’re taking certain medications, EllaOne will not be effective. These include:

  • epilepsy treatment such as carbamazepine, phenytoin and phenobarbital
  • antibiotics used in tuberculosis treatment, such as rifampicin
  • griseofulvin, an antifungal medication
  • efavirenz or nevirapine, which are HIV treatments
  • a herbal remedy used to treat low moods called St John’s wort

These medications can reduce the effectiveness of EllaOne by increasing its metabolism in your liver. This means EllaOne will be cleared from your body too quickly and it will not work.

EllaOne can also be affected by other hormone treatments, including the contraceptive pill or long acting contraceptives like the contraceptive injection or implant. EllaOne may be less effective if you are using another hormone treatment, and might make these treatments less effective too. You should not use your pill or other hormonal contraception for 5 days after taking EllaOne, and should use another form of contraception.

If you’re taking any of these medications and need emergency contraception, speak to your doctor or pharmacist. They may suggest you get the copper intrauterine device (IUD) fitted.

Levonelle effectiveness

Levonelle contains levonorgestrel, a type of synthetic progesterone. Levonelle should be taken as soon as possible after unprotected sex and only within 72 hours.

While Levonelle is less effective than EllaOne, it’s still a suitable choice for emergency contraception. If you cannot take EllaOne for any reason, such as being allergic to the ingredients in the tablet, you can take Levonelle.

If you’re taking medications that reduce the effectiveness of EllaOne, you may still be able to take Levonelle. Speak to your doctor or pharmacist if this is the case. They may recommend taking a double dose of Levonelle to ensure its effectiveness.

Levonelle is a branded name for generic levonorgestrel and is manufactured by Bayer. You can request Levonelle or generic levonorgestrel from Asda Online Doctor.

Levonorgestrel effectiveness

Levonorgestrel is the active ingredient in Levonelle, and you can get it as a generic (non branded) tablet.

This means that levonorgestrel is just as effective as Levonelle for preventing unplanned pregnancy if you take it within 72 hours. Levonorgestrel is most effective, around 99%, if you take it within 24 hours after unprotected sex.

What can make the morning after pill less effective?

There are a few things that can make both morning after pills less effective. If you take the morning after pill after you have ovulated, neither pill will work. Both types of morning after pill are designed to prevent pregnancy by delaying ovulation.

Some medications can reduce the effectiveness of the morning after pill. Speak to your doctor or pharmacist if you’re unsure if your medications will do this. They may advise you to see a sexual health clinic to get the copper IUD fitted.

If you vomit within 3 hours of taking either morning after pill, you’ll need to get another dose as the medication will not have been absorbed by your body.

If you have unprotected sex after you’ve had the morning after pill, the pill will not work for the second instance of sex. You’ll need to take another morning after pill to cover yourself for this.

There’s some evidence to suggest that if you have a high body mass index (BMI), the morning after pill will not be as effective. If your BMI is higher than 26 or your weight is more than 70 kg, speak to your doctor or pharmacist. They may suggest taking either EllaOne or a double dose of Levonelle. If your BMI is higher than 30 then neither pill may be effective.

If you take EllaOne and are on birth control pills, you’ll need to use extra contraception or avoid sex for at least 5 days after taking EllaOne. Birth control pills can contain synthetic progesterone (like desogestrel). Ulipristal acetate works on the same receptors as progesterone. This means EllaOne can reduce the effectiveness of your usual contraceptive pills.

You can take either morning after pill more than once in the same menstrual cycle if you have unprotected sex again. Morning after pills are not designed to be used as regular contraception. The combined pill or mini pill are much more effective methods of contraception. There are also other forms of contraception, such as condoms, that you can try if you want to avoid using hormones. Keep in mind that repeated use of any morning after pill can give you side effects, such as irregularities with your periods, and you are more likely to become pregnant compared to regular contraception.

Is the morning after pill less effective when ovulating?

The morning after pill can be less effective if you take it when you are ovulating. EllaOne, Levonelle, and levonorgestrel will all not work after you have ovulated.

Ovulation is triggered by a large increase in luteinizing hormone (LH). EllaOne can still be effective if you take it just before the LH surge, whereas levonorgestrel will not be as effective.

In both cases, it can be risky to take the morning after pill just as ovulation begins as it’s hard to predict when you are exactly ovulating. You can take the morning after pill as a precaution but be aware that there is a chance you may still get pregnant. If this happens, do a pregnancy test at least a couple of weeks after you’ve had unprotected sex.

Can you get pregnant after taking the morning after pill?

You can still get pregnant after taking the morning after pill. No contraceptive method is 100% effective and there’s always a chance of pregnancy whenever you have sex.

Getting the copper IUD fitted is the most effective type of emergency contraception as it has a more than 99% effectiveness rate. The copper IUD gets to work immediately as soon as it is fitted inside your uterus and lasts for around 5 to 10 years. This means you do not need to worry about remembering to take a pill.

Does the morning after pill protect you against STIs?

Both EllaOne and Levonelle do not protect you against sexually transmitted infections (STIs). Only the barrier method can protect you against STIs, such as condoms or female condoms.

Medically reviewed by:
Dr Kathryn Basford

Dr Kathryn Basford is a qualified GP who works as a GP in London, as well as with ZAVA. She graduated from the University of Manchester and completed her GP training through Whipps Cross Hospital in London.

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Article created: 17 May 2022

You might need emergency contraception if you’ve recently had unprotected sex and want to reduce your risk of getting pregnant. Asda Online Doctor by ZAVA offers a morning after pill service, which includes a variety of options.

(Reviews are for ZAVA UK)

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