Had unprotected sex, or had your contraception fail? You've got a short window to act, so it helps to know your options before you get to 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 it is in that window, and how it affects you afterwards.
This guide sets out the evidence on all three, plus the side effects and what to do next, so you can make an informed choice.
Whichever pill you choose, the sooner you take it, the better it works.
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 you take it, ideally within 12 hours.2
- How they work - both mainly work by delaying ovulation. But they're different medicines with different effects on your cycle, so the choice isn't just about timing.1,2
Within 72 hours? Either pill is an option for most people. Beyond 72 hours, ellaOne is the only pill option.
A copper IUD (coil), fitted by a clinician, is more effective than either pill. It can be used up to 5 days after sex, or up to 5 days after your earliest likely ovulation date, if you'd rather discuss that route with a clinic.4
The copper coil is the most effective emergency option, and once it's fitted, it carries on working as your regular contraception.
How does each pill work?
Both pills work by interrupting ovulation, not by ending a pregnancy that's already started. Neither works once implantation has begun.
ellaOne (ulipristal acetate)
Ulipristal acetate is a selective progesterone receptor modulator. In plain English, it acts on your body's receptors for progesterone, a key hormone in your cycle. This holds back the hormone surge that triggers ovulation, which is why it keeps working later in your cycle than levonorgestrel.
In clinical studies, a single dose taken even after this hormone surge had started postponed ovulation for at least 5 days in around 79% of cases. That compares with roughly 14% for levonorgestrel and 10% for a placebo taken at the same point in the cycle.3
It's the main reason ellaOne still works closer to ovulation, when levonorgestrel's effectiveness has largely dropped away.
Close to ovulation is where the two pills differ most, and it's hard to know exactly when that is.
Levonelle (levonorgestrel)
Levonelle contains a higher dose of a progestogen, the same type of hormone found in many regular contraceptive pills. It mainly works by stopping or delaying ovulation, if you take it before the hormone surge begins.
Once that surge is underway, levonorgestrel is much less effective. That's why timing matters more with this option.2
Which is more effective?
Comparing ellaOne vs levonorgestrel on effectiveness comes down to the trial data. In studies comparing the two directly within 72 hours of unprotected sex, ellaOne was linked to a lower pregnancy rate than levonorgestrel.
A combined analysis of two randomised trials found a pregnancy rate of 1.36% with ellaOne, against 2.15% with levonorgestrel. That's a statistically significant difference.1
Later in the licensed window, between 72 and 120 hours after sex, ellaOne still works. Pregnancy rates in trials ranged from 0% to around 2%, though there's less data for this later period than for the first 72 hours.1
Does body weight matter? Possibly. The evidence is limited and doesn't point clearly in one direction, but some studies suggest both pills may work less well at a higher body weight or BMI. Both manufacturers mention this.1,2
Whatever your weight, take your pill as soon as you can after unprotected sex. That's what makes the biggest difference in practice.
Worried your weight or BMI might affect how well either pill works? Ask a pharmacist whether a copper IUD would be a more effective option for you.
Side effects compared
Both pills are generally well tolerated. Most side effects are mild and settle within a day or two.
These are the more commonly reported side effects with ellaOne.1
- Headache and dizziness - common
- Nausea and tummy pain - common
- Period changes - your next period may come earlier or later than expected. In trials, around 1 in 5 women had a delay of more than 7 days.
- Mood changes and tiredness - common, and usually mild
And these are the more commonly reported side effects with Levonelle.2
- Headache, nausea and lower tummy pain - very common
- Tiredness - very common
- Dizziness - common
- Period changes - bleeding between periods is very common, and your next period may come earlier or later than expected
Severe lower tummy pain in the weeks after taking either pill needs urgent checking. It can be a sign of an ectopic pregnancy.
Vomit within 3 hours of taking either pill? Speak to a pharmacist or your GP straight away. It can stop the pill working, and you may need another dose or a different method.1,2
Does emergency contraception affect your future fertility?
Neither pill has any lasting effect on your fertility. In fact, both product licences say your fertility is likely to return quickly after treatment. That's exactly why a barrier method matters afterwards.1,2
Do not rely on the morning after pill to cover sex later in the same cycle. It only protects against sex that's already happened.
So future fertility doesn't need to factor into choosing between ellaOne vs levonorgestrel. If your periods are irregular for a cycle or two afterwards, that's a short-term hormonal effect, not a sign of a longer-term problem.
Can you switch or combine ellaOne and Levonelle?
Do not take ellaOne and levonorgestrel emergency contraception together, or one shortly after the other.1 Progestogens, including levonorgestrel, can reduce ellaOne's ability to delay ovulation. So combining them may make ellaOne less effective, rather than adding extra protection.
Restarting your regular contraception works differently too. UK clinical guidance says that after Levonelle, you can start or carry on with your usual hormonal contraception straight away. You'll just need condoms for a short time, depending on your method.4
After ellaOne, the same guidance says to wait 5 days before restarting hormonal contraception. That's because the hormones in your regular contraception could stop ellaOne working properly.4 Either way, use a barrier method such as condoms until your next period.
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 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
Frequently asked questions
What's the difference between ellaOne and levonorgestrel?
ellaOne contains ulipristal acetate and is licensed for up to 120 hours (5 days) after unprotected sex. Levonorgestrel (Levonelle) works up to 72 hours (3 days) and is most effective taken within 12 hours. Both delay ovulation, but ellaOne stays effective for longer and, based on head-to-head trial data, works somewhat better even within the first 3 days.
ellaOne works by delaying the hormone surge that triggers ovulation. Unlike levonorgestrel, it can still postpone ovulation even if that surge has already started, which is why it remains effective later in the fertile window. It does not end an existing pregnancy.
Which is more effective, ellaOne or levonorgestrel?
In trials comparing the two within 72 hours of unprotected sex, ellaOne (ulipristal acetate) was associated with a lower pregnancy rate than levonorgestrel, 1.36% versus 2.15%, a statistically significant difference. Taking either pill as soon as possible after sex has the biggest impact on how well it works.
What are the side effects of ellaOne and Levonelle?
Both are generally well tolerated. Common side effects of ellaOne include headache, dizziness, nausea and abdominal pain. Levonelle's most frequently reported effects, headache and nausea, are classed as very common, occurring more often than with ellaOne. Speak to a pharmacist if side effects are severe or persistent.
Can I take Levonelle after taking ellaOne?
No, this is not recommended. Levonorgestrel can reduce ellaOne's ability to delay ovulation, so combining them may make ellaOne less effective rather than adding extra protection. If you're not sure which pill is right for you, ask a pharmacist before taking either.
Can ellaOne or Levonelle delay your period?
Yes, both can shift your next period earlier or later than expected. With ellaOne, around 1 in 5 women experience a delay of more than 7 days. If your period is more than 5 to 7 days late, take a pregnancy test to rule out pregnancy.
Do ellaOne or Levonelle affect future fertility?
No, neither pill has any lasting effect on fertility. Both are licensed on the basis that a rapid return of fertility is expected once the cycle has passed, which is why using a barrier method afterwards matters until your next period.
References
- Electronic Medicines Compendium. Ulipristal 30mg film-coated tablets, Summary of Product Characteristics. Zentiva; 2023. medicines.org.uk/emc
- Electronic Medicines Compendium. Levonelle 1500 microgram tablet, Summary of Product Characteristics. Bayer plc; 2021. medicines.org.uk/emc
- 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.
- 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.