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How and when to take Pre-Exposure Prophylaxis (PrEP)

PrEP is a prescription medicine that you can get from a sexual health clinic. It may not fully protect you if you do not take it correctly. It's important to take it as advised by your clinic doctor.

PrEP comes as tablets.

Depending on how regularly you have sex and what type of sex you have, you can take them in 2 different ways: every day, or when you need it (on demand).

Daily PrEP (for vaginal/frontal sex and anal sex)

Taking PrEP daily provides protection for vaginal/frontal and anal sex.

How to take it

Take 1 tablet every day day, around the same time each day. Wait 7 days after you start taking it before you have sex.

If you want to start taking daily PrEP but think you may have sex within the first 7 days, take 2 tablets at least 2 hours before you have sex. Then continue to take 1 tablet each day.

It's better to take PrEP with or after food.

If you're sick (vomit) within 1 hour of taking PrEP, take another tablet. If you're sick more than 1 hour after taking PrEP, do not take another tablet.

If you have difficulty swallowing tablets, you can crush PrEP and mix it with a drink of water, orange juice or grape juice.

If you forget to take it

If you take PrEP every day and miss your dose, you can still take it as long as it's within 12 hours of when you were supposed to take it. If it's longer than 12 hours, you'll have to miss that dose and take the next one at the usual time.

It's important not to miss your dose but if that does happen, it's OK. However, for full protection, you must have taken at least 6 daily doses in the past week.

If you miss more than 2 of your doses in a week, ask the doctor at your clinic for advice.

If you do not take your PrEP tablets for a week or more, you'll have to start again. Do not take more than 2 tablets when you start PrEP.

Do not take more than a total of 7 pills in 1 week, unless you started with 2 doses.

If you forget doses often it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.


If you forget to take your PrEP doses often, you can use the PrEP time tracking app to set tablet reminders and track your daily or on-demand doses.

Stopping daily PrEP

If you have had vaginal/frontal sex, take your daily dose for 7 more days after the last time you had sex. It is then OK to stop.

PrEP on-demand (for anal sex only)

Taking PrEP on demand will give you protection against HIV during anal sex.

PrEP on demand is not recommended for vaginal/frontal sex.

Do not use on-demand dosing if you have hepatitis B because PrEP can affect the hepatitis B virus. Starting and stopping PrEP can make the virus more active and this can lead to liver inflammation.

How to take PrEP on demand

If you want to take PrEP on demand, follow these steps:

  • take 2 tablets between 2 and 24 hours before having anal sex
  • take 1 tablet 24 hours later
  • take 1 tablet 24 hours after that

If you're continuing to have sex over a period of time, carry on taking 1 pill every 24 hours until you have not had sex for 2 days.

If you have difficulty swallowing tablets, you can crush PrEP and mix it with a drink of water, orange juice or grape juice.

Stopping PrEP on demand

If you have had anal sex, take your daily dose for 2 more days after the last time you had sex. It's then OK to stop.

Check with your clinic before stopping. Stopping taking this medicine or missing doses may increase your risk of getting HIV infection.

How long to take it for

As long as you have regular tests, you can take PrEP for a long time.

Before you start taking PrEP, you'll be recommended to have:

  • a test for HIV and other STIs – you'll need to continue to have these regularly, for example, every 3 months
  • a hepatitis B test – to confirm you do not have a hepatitis B infection
  • a blood test to check your kidney function – using PrEP can reduce kidney function, so it's important to know if you have pre-existing kidney issues or are taking medicine that may affect your kidneys

If you are over 40 or already have issues with your kidney function, you may need more regular kidney function tests. Check how often you need to do this with your clinic doctor.

If your doctor has any concerns about your blood test results, they may talk to you about stopping PrEP treatment.

PrEP protection

If you have been taking PrEP for 7 days, you are still protected, even if you miss the occasional dose.

If you have been taking PrEP daily, you must have taken at least 6 doses in the past week to still be protected.

If you take too much

Urgent advice: Contact 111 for advice now if:

  • you take 3 PrEP tablets or more at the same time

Go to or call 111

If you need to go to A&E, do not drive yourself. Get someone else to drive you or call for an ambulance.

Take the PrEP packet, or the leaflet inside it, plus any remaining medicine with you.

Page last reviewed: 10 March 2023
Next review due: 10 March 2026