Most women know what emergency contraception, or the morning after pill, is. But relatively few know all the details.
When you need the morning after pill, you have to make decisions quickly. Which pill suits you, how long you have and what to do afterwards can all make a difference. Here are five things worth knowing before you ever need them.
Whichever pill you take, the sooner you take it, the better it works.
1. There are two morning after pills, and they cover different time windows
The two morning after pills available in the UK are ellaOne (ulipristal acetate 30mg) and Levonelle (levonorgestrel 1.5mg). Both are emergency contraceptives, but they work to different deadlines.
Levonelle needs to be taken within 72 hours (three days) of unprotected sex. ellaOne can be taken up to 120 hours (five days) afterwards.1
ellaOne has also been shown to be more effective than Levonelle overall.2 So within 72 hours, both are options. Between 72 and 120 hours, ellaOne is the pill to ask for.
Missed the three-day mark? You haven't missed your chance. ellaOne covers you for up to five days.
2. The sooner you take it, the better it works
Both morning after pills work mainly by delaying ovulation, the release of an egg. Neither is a form of abortion, and there's no evidence either one harms a pregnancy that's already started.2
Because they work by stopping ovulation before it happens, timing matters. The sooner you take one, the more likely it is to work.1
No emergency pill is 100% effective. Research suggests around 1 to 2 in every 100 women who take one will get pregnant.1 The copper coil (IUD) is the most effective form of emergency contraception, so it's worth knowing about too.1
Both pills are available from UK pharmacies without a prescription. You can also order emergency contraception online through a registered UK pharmacy, without a GP appointment.
3. Your weight may affect which option suits you best
This is one of the least well-known things about the morning after pill. Levonorgestrel pills like Levonelle may work less well at a higher body weight or body mass index (BMI).
The College of Sexual and Reproductive Healthcare (formerly the FSRH) advises that Levonelle could be less effective if you weigh more than 70kg or have a BMI above 26.2
If that applies to you, the guidance suggests ellaOne instead. If ellaOne isn't suitable, a double dose of levonorgestrel can be used, although how well that works isn't known.2 A copper IUD is also an option, and its effectiveness isn't known to be affected by weight.2
Weigh over 70kg, or have a BMI above 26? Mention it in your consultation, as it can change which option is best for you.
Not sure which option is right for you? Ask the pharmacist before you buy. They can advise based on your circumstances.
4. Side effects are normal, and a late period doesn't mean it's failed
After taking the morning after pill, it's common to have a headache, nausea or period-type pain. Some women also notice tummy pain, tiredness or irregular bleeding. These usually pass without treatment.2,3
Emergency contraception can also change the timing of your next period, so it may come a little earlier or later than usual.3,4 That on its own doesn't mean the pill hasn't worked.
Either way, do a pregnancy test three weeks after the last time you had unprotected sex, even if you've had some bleeding since.2 Test sooner and get advice if your period is late or much lighter than normal.
If you're sick within three hours of taking either pill, it may not have been absorbed. Contact a pharmacist or GP as soon as possible, as you'll need another dose.2
Rarely, a pregnancy can still happen after the morning after pill, and it may be outside the womb (ectopic).3
Severe pain low down on one side of your tummy in the weeks after taking it? Get urgent medical help, as it can be a sign of an ectopic pregnancy.
5. It's worth having emergency contraception at home before you need it
Emergency pills keep for a long time. Levonelle, for example, has a shelf life of five years.3 So buying one in advance is a practical option, not an unusual one.
Because timing matters so much, having a pill at home means you can take it straight away if you need it. No hunting for an open pharmacy or waiting for a delivery.
You can order emergency contraception online through Pharmica after a short consultation, with no GP appointment. If you do keep one at home, check the expiry date every so often and replace it when needed.
One thing to know: the morning after pill only covers sex that's already happened. It won't protect you if you have unprotected sex again afterwards.2
What you do next depends on which pill you took:
- After Levonelle - you can usually start or restart hormonal contraception straight away. Use condoms or avoid sex until it's working.2
- After ellaOne - wait five days before starting or restarting hormonal contraception, as it can make ellaOne less effective. Use condoms or avoid sex during those five days, and then until your contraception is working.2
Do not start hormonal contraception within five days of taking ellaOne unless a pharmacist or doctor has advised it.
Your pharmacist can give you an exact plan, especially if you've missed pills. And if you find yourself needing emergency contraception regularly, speak to a pharmacist or GP about a longer-term method.
Frequently asked questions
How effective is the morning after pill?
Both pills are most effective when taken as early as possible. Levonelle is up to 95% effective within 24 hours of unprotected sex, falling to around 85% between 25 and 48 hours, and 58% between 49 and 72 hours.1 ellaOne is considered more effective later in its window and remains suitable for up to 120 hours.2 No morning after pill is 100% effective, and neither is a substitute for regular contraception.
How does the morning after pill work?
Both pills work primarily by delaying or preventing ovulation - the release of an egg - so that fertilisation cannot occur. They do not cause an abortion and have no effect if you are already pregnant.1 ellaOne (ulipristal acetate) works by blocking the action of progesterone to delay ovulation. Levonorgestrel works by mimicking a hormone that prevents the ovaries from releasing an egg.2
Can the morning after pill delay your period?
Yes. It is common for the morning after pill to shift your next period by a few days to a week, either earlier or later than expected.4 This is a normal hormonal effect and does not mean the pill has not worked. If your period is more than seven days late or significantly lighter than usual, take a pregnancy test.
Can I take the morning after pill more than once?
There is no medical reason you cannot take the morning after pill more than once, including within the same menstrual cycle. However, it is not designed to replace regular contraception and becomes less reliable with repeated use within a single cycle.1 If you are finding yourself using it frequently, speak to a pharmacist or GP about long-term contraceptive options.
References
- NHS. How to take the emergency contraceptive pill (morning after pill). NHS website; 2024. nhs.uk
- Faculty of Sexual and Reproductive Healthcare. Emergency Contraception (March 2017, amended April 2026). College of Sexual and Reproductive Healthcare; 2026. cosrh.org
- Gedeon Richter Plc. Levonelle 1500 microgram tablet: Summary of Product Characteristics. Electronic Medicines Compendium; 2021. medicines.org.uk/emc
- Zentiva Pharma UK Limited. Ulipristal 30mg film-coated tablets: Summary of Product Characteristics. Electronic Medicines Compendium; 2023. medicines.org.uk/emc
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.