Reviewed June 2019

Levonelle or EllaOne? How the morning after pill works

Two types of morning after pills against a colourful background

The morning after pill, a form of emergency contraception, can be an extremely useful and effective way of preventing accidental pregnancy. There are two kinds of branded emergency contraceptive pill, one called Levonelle and one called ellaOne. The other form of emergency contraception sometimes used, apart from own-brand morning after pills, is the IUD, or copper coil, which can be used up to five days after sex has taken place.

The morning after pill should be taken as soon after unprotected intercourse (or failed contraception) as you can. It can also be used if you have missed two or more contraceptive pills in a pack. The earlier it is taken after unprotected sex, the more effective it is.1

You can get the morning after pill at most GP surgeries, some GUM and sexual health clinics, and community contraception clinics. Most NHS walk in centres and accident and emergency departments also stock the morning after pill. It is also available to buy at most pharmacies following a short consultation with the pharmacist, or even from online doctors.

Levonelle has to be taken within 72 hours (three days) of intercourse, while ellaOne has a slightly longer window and needs to be taken within 120 hours (five days) of having intercourse.2 But is one better than the other? And how does the morning after pill actually work?

How does the morning after pill work?

Levonelle has been used as a form of emergency contraception for many years. It contains the hormone levonorgestrel, a synthetic (man-made) version of progesterone. Levonelle is thought to work mainly by preventing or delaying ovulation (the release of the egg).

In a woman’s normal menstrual cycle, an egg matures and is released (ovulation). The ovary then produces progesterone to stop the release of further eggs. It is believed that the levonorgestrel in Levonelle tricks the body into thinking that ovulation has already occurred (due to the high levels of synthetic progesterone), preventing the release of the egg. Levonorgestrel also causes an increase in the thickness of mucus in the cervix forming a barrier to make it difficult for sperm enter the womb.

There are generic versions of Levonelle available. These contain the same amount and type of levonorgestrel and will be equally effective, but do not have the trade name. Generic equivalents may be simply called levonorgestrel 1.5mg, levonorgestrel 1500, or Ezinelle. Typically, they are significantly cheaper than the branded version of the product.

EllaOne is a newer form of emergency contraceptive pill that is thought to be more effective than Levonelle in certain scenarios, including in that you have longer to take it.

The active ingredient in ellaOne is called ulipristal acetate. This is called a selective progesterone receptor modulator that works by modifying the activity of the natural hormone progesterone in the woman by acting on the body’s progesterone receptors,3 making them think that there are higher levels of circulating progesterone than there actually are. Ulipristal tricks the body into believing that ovulation has already occurred, resulting in ovulation being delayed or completely prevented.

How effective is the morning after pill?

Both Levonelle and ellaOne are generally effective only if taken before the release of an egg from the ovary (ovulation), i.e early on in the cycle. The sooner you take them, the more effective they will be. If you have unprotected sex in the 24 hour window immediately after ovulation, the period of time when the released egg can still be fertilised, then taking emergency contraception after this is unlikely to be effective, although the morning after pill may make the uterus environment less receptive to implantation, so there is a possibility that pregnancy could still be prevented.

Levonelle and ellaOne are thought to be equally effective up to 12 hours after unprotected intercourse (95% effective), however the efficacy of Levonelle then starts to tail off, down to 58% effective after 48 hours after intercourse.4

This is compared to ellaOne which is up to 95% effective up to 120 hours after intercourse. The bottom line is if you take the morning after pill very soon after unprotected intercourse it probably does not matter which type you take, however, if it was more than 12 to 24 hours ago, then ellaOne may be more effective.5

Side effects of emergency contraception

Both Levonelle and ellaOne can cause some side effects including sickness, feeling dizzy and tired, headaches, tender breasts, or abdominal pain. They may also result in your period coming earlier or later than normal, or making it heavier than you would otherwise expect. The main reason for these side effects is the relatively high dose of progesterone that the morning after pill gives. These side effects may therefore be similar to those you feel just before you get your period (when your progesterone levels are naturally high).

Taking the emergency contraceptive pill three or more days before your usual ovulation date is likely to make your next period come early as well, as it tricks the body into thinking that ovulation has already occurred.

Who can use the emergency contraceptive pill?

Most women can safely use the emergency contraceptive pill, but ellaOne should not be used by women with severe asthma (on steroid tablets), or those with certain rare inherited problems of lactose breakdown. ellaOne should also ideally be avoided in breastfeeding mothers as there is little safety data on breastfeeding after taking this medication.

There are no stated medical conditions that mean Levonelle cannot be used. Smoking does not interfere with how either preparation works.

Factors that can affect how effective the morning after pill is

Women who are on certain medications may find that emergency contraception is less effective. These medications include St John’s Wort (over the counter treatment for low mood), certain epilepsy medications or other enzyme inducing drugs.5 Medications for heartburn called proton pump inhibitors (PPI’s) such as omeprazole can also interfere with absorption.6 In these cases, ellaOne should not be used, and Levonelle should be the emergency contraceptive of choice.

There is some evidence to suggest that both forms of emergency contraception are less effective with increasing body weight, but data is limited. A high body weight is thought to be less likely to affect ellaOne, so women with a high BMI may be better off taking ellaOne (dependent on other medications they may be taking).

How to take emergency contraception

Take the medication as soon as you can with water. If you are sick within 2 hours of taking Levonelle or 3 hours of taking ellaOne, please seek medical advice as you will need a further dose or use alternative emergency contraception.

There is no evidence to suggest that emergency contraceptive pills increase your risk of having an ectopic pregnancy. Because emergency contraceptive pills reduce your risk of pregnancy, theoretically, they also reduce your risk of ectopic pregnancy too.

However, occasionally, ectopic pregnancies can still occur after a woman uses an emergency contraceptive pill, so if you develop abdominal pain around when your period is due after taking morning after pill, or if your period is lighter than normal, please see your doctor.

If you are concerned about any symptoms after taking the emergency contraceptive pill, contact your GP or nurse at a sexual health clinic.

You may be able to get the emergency contraceptive pill in advance of having unprotected sex if you are worried about contraceptive failure, you are going on holiday, or you cannot get hold of emergency contraception easily. This needs to be discussed with your GP.

Levonelle and ellaOne do not stop you becoming pregnant later in your cycle if you have unprotected intercourse again so alternative contraception must be used. They are also not designed to be used as regular forms of contraception but can be used more than once in a cycle if necessary. Emergency contraception also does not protect against sexually transmitted infections (STIs) so please get yourself checked out at a GUM clinic if this is needed.
Featured image is a packet of two different types of emergency contraceptive pills, lying next to each other against a colourful background
Last updated June 2019
Next update due 2022

Dr. Jennifer Kelly, MBChB(hons) MRCGP DRCOG

Jennifer is a General Practitioner, medical writer, parent, and founder of the Grace Kelly Ladybird Trust, registered charity for childhood cancer awareness and research. She also has a particular interest in women’s and children’s health, and enjoys medical writing, particularly helping make medical information easily accessible to those who want to find out more.

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  1. NHS, Emergency contraception (morning after pill, IUD), NHS website [website]: (accessed 24 June 2019) 
  2. FSRH Clinical Effectiveness Unit, ‘Emergency Contraception’, CEU Clinical Guidance, FSRH, March 2017,, (accessed 24 June 2019).
  3. Jadav, S.P., Ulipristal acetate, a progesterone receptor modular for emergency contraception, Journal of Pharmacology & Pharmacotherapeutics, 2012, vol 3, issue 2, pp 109-111
  4. Bayer plc, Levonelle One Step, [website], (accessed 24 June 2019)
  5. NICE, Contraception – emergency; Scenario: Emergency contraception, NICE guidelines, last revised February 2017, [website]:!scenario (accessed 24 June 2019)
  6. GP notebook, Ulipristal acetate (ellaOne) postcoital contraception, [website]: (accessed 24 June 2019)

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