Plan B Pill: How it works & who can take it

Dr. Babak Ashrafi

Medically reviewed by

Dr Babak Ashrafi

Last reviewed: 23 Jan 2023

The plan B pill is another name for the morning after pill. It is an effective and safe method to prevent pregnancy after having unprotected sex. The Plan B pill is also an American brand name used for a morning after pill available in the US, but the term ‘plan B pill’ is often used to refer to other emergency contraceptives. In the UK, the term ‘plan B pill’ would likely be used to describe treatments like ellaOne, Levonelle and generic levonorgestrel, all of which are morning after pills.

woman takes the plan b pill with a glass of water

Key takeaways

  • The plan B, or morning after, pill is a type of emergency contraception available in the US. The UK has equivalent pills that work in the same or a very similar way, such as Levonelle, generic Levonelle, and ellaOne. The active ingredient in a Plan B branded pill in the US is levonorgestrel, the same as in Levonelle.

  • The plan B pill can prevent pregnancy when taken up to 72 or 120 hours after having unprotected sex. However, the time window in which you have to take it depends on the type of pill you use. A plan B pill can also be used if the condom split, or if you missed a dose of your contraceptive pill.

  • The plan B pill is suitable for most women, but you should speak to your doctor if you take any other medications.

  • The plan B pill can cause some side effects, such as headaches, nausea, vomiting, and changes to your period. It does not cause any serious or long-lasting effects.

How does the plan B pill work?

The plan B pill is a type of emergency contraception. It can prevent pregnancy when taken after unprotected sex or if other forms of contraception have not worked. It cannot end a pregnancy and will not cause an abortion. It also does not protect you from catching an STI.

Levonelle is a plan B pill that contains a man-made version of levonorgestrel, a type of female progesterone hormone. This can stop or delay ovulation, which is when your body releases an egg to be fertilised. You can take this up to 72 hours after unprotected sex.

ellaOne is another type of plan B pill available in the UK. It contains the active ingredient ulipristal acetate, which can stop progesterone from working as it should. This can also stop or delay your ovaries from releasing an egg. Although the active ingredient in ellaOne is different to Levonelle or Plan B branded pills, they are both just as effective treatments. Levonelle is 95% effective when taken in the first 24 hours after unprotected sex, while ellaOne is 98% effective. EllaOne can be taken up to 120 hours after unprotected sex.

from £18.95

from £29.95

from £11.95

No results found.

No results found.
Please check your spelling or try another treatment name.

Who can take it

The plan B pill is safe for most women to take, including women who cannot take the combined contraceptive pill.

It is safe to take if you are already using contraceptives like the patch, ring, injection, or daily pill. However, you should speak to your doctor if you use any kind of hormonal contraception, as you may need to wait before taking your next dose.

You may be unsuitable for the morning after pill if you have an allergy to any of the ingredients, have severe asthma, or take certain medications, such as:

  • medicines to treat HIV, epilepsy, or tuberculosis (TB)
  • St John’s wort, a herbal medicine
  • medicine to lower stomach acid levels, like omeprazole
  • antibiotics called rifampicin and rifabutin

ellaOne is not suitable if you take the above medications because they can reduce how effective it is. Levonelle may still be suitable for you, but you must consult a doctor or nurse first, as they may prescribe a higher dose. If you are not sure if the plan B pill is suitable for you, speak to a pharmacist or doctor.

ellaOne can interact with other contraceptives and make them less effective, so you may need to use a condom if you have sex after taking it.

You can take Levonelle if you are breastfeeding but should wait 8 hours after taking it to breastfeed again. There is not enough research into breastfeeding after taking ellaOne, so it is not recommended to breastfeed for a week after you have taken it. You should not use the plan B pill if you are already pregnant.

When to take a plan B pill

The plan B pill should be taken within 3 days (72 hours) of unprotected sex if you are using Levonelle or the generic levonorgestrel, or 5 days (120 hours) if you are using ellaOne.

The sooner you take it after sex, the more effective it will be, and the less chance you will have of getting pregnant.

How to take it

Depending which “Plan B” you’re taking will affect how and when you take it.

Levonelle and levonorgestrel should be taken as a single dose up to 72 hours (3 days) after sex. It will be most effective if taken within 12 hours. ellaOne should be taken as a single dose up to 120 hours (5 days) after sex. ellaOne is suitable if it is longer than 72 hours since you had sex.

Both can be taken with or without food. If you vomit (are sick) or have diarrhoea within 3 hours of taking the pill, you must speak to your doctor, sexual health clinic, or pharmacist. You will need to take another pill to prevent pregnancy, as your body has not had enough time to absorb the medication. In some cases, if you vomit, you may need to have an intrauterine device (IUD) fitted.

Are there any side effects?

The plan B pills available in the UK have no long term or serious side effects. You are most likely to get any side effects within a couple of hours, and they should go away within a few days. The most common side effects include:

  • stomach pain
  • headaches
  • changes to your period, such as being early, late, or more painful than usual
  • nausea or vomiting (feeling or being sick)

You should speak to your doctor if your symptoms last longer than a few days or if you think you might be pregnant. The plan B pill can delay your period by a few days but not usually longer than a week, so take a pregnancy test if your period is delayed by more than 7 days.

Where can I get the plan B pill?

The Plan B pill brand is only available in the US, but the UK has alternatives that work in the same or a very similar way. In the US, emergency contraceptives are sometimes generally referred to as ‘the plan B pill’, whereas, in the UK, they are often referred to as the ‘morning after pill’. You can get the morning after pill online from ZAVA. We currently have a range of options available, such as Levonelle, Generic Levonelle (levonorgestrel), and ellaOne. You can also visit a pharmacy, GP, or your local sexual health clinic.

Plan B pill FAQS

Can the plan B pill delay your period?

The plan B pill can delay your period for up to 5 days, though occasionally, it can be more delayed. If your period is more than 7 days later than you expect, take a pregnancy test and speak to your doctor. Emergency contraceptives should not be used as a period delay treatment.

Is the plan B pill available over the counter?

Yes, you can get the plan B pill over the counter at your local pharmacy. The pharmacist will normally ask you a few questions first to make sure that emergency contraception is suitable for you and that it is safe for you to take.

Which plan B pill is the most effective?

Both Levonelle and ellaOne are effective at preventing pregnancy but are most effective the sooner they are taken after sex. Both are only effective when taken before ovulation occurs (the release of an egg from the ovary).

It is estimated that between 1 and 2% of women who take ellaOne as directed after unprotected sex will get pregnant. For women who take Levonelle as directed, it is estimated between 0.6 and 2.6% will get pregnant after unprotected sex. The main reason to choose one of these options over the other is whether you had unprotected sex (or sex where other contraception failed) within 72 hours (3 days) or within 120 hours (5 days).

Levonelle and ellaOne can be less effective if you have a high body mass index (BMI).

The most effective form of emergency contraception is the intrauterine device (IUD), which is a copper device inserted into your womb by a nurse or doctor.

Will the plan B pill work if you’re ovulating?

The plan B pill can stop or delay the release of an egg, which is called ovulation. This means it can only work before ovulation. If ovulation has already happened, it will not be effective, and you should get a copper coil (IUD) inserted by your GP or local sexual health clinic.

Medically reviewed by:
Dr Babak Ashrafi Clinical Lead for Service Expansion

Babak studied medicine at King’s College London and graduated in 2003, having also gained a bachelor’s degree in Physiology during his time there. He completed his general practice (GP) training in East London, where he worked for a number of years as a partner at a large inner-city GP practice. He completed the Royal College of GPs membership exam in 2007.

Meet our doctors

Last reviewed: 23 Jan 2023

gmc logo GPC logo

Authorised and regulated by