ellaOne vs Levonorgestrel: comparing morning after pills

If you've had unprotected sex or a contraceptive method has failed, you have a short window to act, and it helps to know your options before you reach the pharmacy counter. ellaOne and Levonelle (levonorgestrel) are the two emergency contraceptive pills available in the UK. Comparing ellaOne vs levonorgestrel comes down to three things: how long after sex each one works, how effective they are in that window, and their effects on you afterwards.

This guide sets out the evidence on all three, plus the side effects, cost and access routes for each, so you can make an informed choice.

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ellaOne vs levonorgestrel: what's the difference?

At a glance:

• ellaOne contains ulipristal acetate. It's licensed for use up to 120 hours (5 days) after unprotected sex.¹
• Levonelle contains levonorgestrel. It's licensed for use up to 72 hours (3 days), and works best the sooner it's taken, ideally within 12 hours.²
• Both work primarily by delaying ovulation, but they're different molecules with different effects on the reproductive cycle, and the choice between them isn't just about timing.^1,2

For most people who present within 72 hours, either pill is an option. Beyond 72 hours, ellaOne is the only oral option. A copper IUD, fitted by a clinician, is more effective than either pill and can be used up to 5 days after sex, or up to 5 days after the earliest likely ovulation date, if you'd rather discuss that route with a clinic.⁴

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How does each pill work?

Both pills work by interrupting ovulation rather than by ending an established pregnancy. Neither is effective once implantation has already begun.

ellaOne (ulipristal acetate)

Ulipristal acetate is a selective progesterone receptor modulator. It suppresses the hormone surge that triggers ovulation, which is why it keeps working later in the cycle than levonorgestrel. In clinical studies, a single dose of ulipristal acetate taken even after this hormone surge had already started postponed ovulation for at least 5 days in around 79% of cases, compared with roughly 14% for levonorgestrel and 10% for placebo taken at the same point in the cycle.³ This is the main reason ellaOne remains effective closer to ovulation, when levonorgestrel's effectiveness has largely fallen away.

Levonelle (levonorgestrel)

Levonelle contains a higher dose of the same type of hormone (a progestogen) found in many regular contraceptive pills. It works mainly by preventing or delaying ovulation if taken before the hormone surge begins. Once that surge is underway, levonorgestrel is much less effective, which is why timing matters more with this option.²

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Which is more effective?

Comparing ellaOne vs levonorgestrel on effectiveness comes down to the trial data. In studies comparing the two pills directly within 72 hours of unprotected sex, ulipristal acetate (ellaOne) was associated with a lower pregnancy rate than levonorgestrel. A combined analysis of two randomised trials found a pregnancy rate of 1.36% with ulipristal acetate against 2.15% with levonorgestrel, a statistically significant difference.¹ Used later in the licensed window, between 72 and 120 hours after sex, ellaOne is still effective, with pregnancy rates in trials ranging from 0% to around 2%, though there's less data covering this later period than the first 72 hours.¹

Body weight and BMI may also play a role. The evidence here is limited and doesn't point in a single direction for either drug, but some studies suggest reduced effectiveness at higher body weight for both pills, and manufacturers note this explicitly for both products.^1,2 Regardless of weight or BMI, both pills should be taken as soon as possible after unprotected sex, since this is what makes the biggest difference to effectiveness in practice. If you're concerned that your weight or BMI might affect how well either pill works, it's worth asking a pharmacist whether a copper IUD would be a more effective option for you.

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Side effects compared

Both pills are generally well tolerated, and most side effects are mild and settle within a day or two.

ellaOne, the more commonly reported effects include:¹

• Headache and dizziness - common
• Nausea and abdominal pain - common
• Period changes - your next period can arrive earlier or later than expected. In trials, around 1 in 5 women had a delay of more than 7 days
• Mood changes and fatigue - common, usually mild

Levonelle, the more commonly reported effects include:²

• Headache and nausea - very common, reported more frequently than with ellaOne based on the frequency data in each product's prescribing information
• Dizziness and lower abdominal pain - common
• Breast tenderness and fatigue - common
• Period changes - your period can arrive a few days earlier or later than expected

Speak to a pharmacist or your GP if you have severe or persistent vomiting within 2 to 3 hours of taking either pill, as this can affect how well it works and you may need another dose or a different method.

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Does emergency contraception affect your future fertility?

Neither pill has any lasting effect on fertility. Both product licences note that a rapid return of fertility is likely once the treatment cycle has passed, which is exactly why a barrier method matters afterwards.^1,2 Choosing between ellaOne vs levonorgestrel doesn't need to factor in future fertility either way. If your periods do become irregular for a cycle or two after taking either pill, that's a short-term hormonal effect, not a sign of a longer-term problem.

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Can you switch or combine ellaOne and Levonelle?

Concomitant use of ellaOne and levonorgestrel-containing emergency contraception is not recommended, and taking one shortly after the other is not advised.¹ This is because progestogens, including levonorgestrel, can reduce ulipristal acetate's ability to delay ovulation, so combining them may make the ellaOne less effective rather than adding extra protection.

The advice also differs when it comes to restarting your regular contraception afterwards. UK clinical guidance says that after Levonelle, you can start or continue your usual hormonal contraception straight away, using condoms for a short run-in period specific to that method.⁴ After ellaOne, the same guidance recommends waiting 5 days before restarting hormonal contraception, because ulipristal acetate can reduce how well it works in the meantime.⁴ In both cases, use a barrier method such as condoms until your next period.

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When should you seek medical advice?

Speak to a pharmacist, GP or sexual health clinic if:

• Your period is more than 5 to 7 days late, or is unusually light, or you have any other symptoms of pregnancy
• You have severe abdominal pain, particularly one-sided pain, which can occasionally signal an ectopic pregnancy and needs urgent assessment
• You vomit within 2 to 3 hours of taking either pill
• You've already had unprotected sex earlier in the same cycle, as this may affect how well emergency contraception works
• You think you may need emergency contraception again, since neither pill is intended for repeated or routine use, and a pharmacist can talk you through more effective ongoing options

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References

1. Electronic Medicines Compendium. Ulipristal 30mg film-coated tablets, Summary of Product Characteristics. Zentiva; 2023. medicines.org.uk/emc
2. Electronic Medicines Compendium. Levonelle 1500 microgram tablet, Summary of Product Characteristics. Bayer plc; 2021. medicines.org.uk/emc
3. Brache V, et al. Effect of preovulatory administration of ulipristal acetate on follicular rupture. Contraception. 2013;88(5):611-618, as cited in the ellaOne prescribing information.
4. NHS Derbyshire Medicines Management. Management of Emergency Contraception, JAPC guideline. derbyshiremedicinesmanagement.nhs.uk

This article is intended for informational purposes only and does not replace professional medical advice. Always read the patient information leaflet supplied with your medication and speak to a healthcare professional if you have specific concerns.