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How to take PrEP

PrEP must be at a certain level in your body to work properly. It can take time for your body to absorb PrEP. So you need to take it before and after exposure to HIV.

After you start taking PrEP, you need regular testing and monitoring for HIV and STIs.

Testing and monitoring when taking PrEP

Information:

When we mention vaginal on this page, we also mean neovaginal.

Ways to take PrEP

How you take PrEP depends on your circumstances.

There are 2 ways to take PrEP.

Daily dosing

Daily dosing means you take PrEP every day.

For anal sex and insertive vaginal or frontal sex

When you start PrEP, take 2 tablets (double dose) between 2 and 24 hours before sex. This is to make sure that the medicine levels are high enough to be protective before you have sex without a condom.

Continue to take 1 tablet a day.

To stop PrEP, continue to take 1 tablet every 24 hours until you have taken 2 tablets after the last time you had sex.

Stopping PrEP safely

For receptive vaginal or frontal sex and sharing injecting drug equipment

When you start PrEP, take 2 tablets (double dose) between 2 and 24 hours before exposure. This is to make sure that the medicine levels are high enough to be protective before exposure.

Continue to take 1 tablet a day.

To stop PrEP, take 1 tablet every 24 hours until 7 tablets have been taken after your last exposure.

Stopping PrEP safely

Tips for taking daily PrEP

There are things you can do to help take PrEP correctly.

  • Use a medicine box marked with days of the week - this will help reduce the risk of missing a dose.
  • Set a reminder alarm on your phone or use a medicine reminder app.
  • Take your PrEP at same time each day - for example, link it to a routine task like brushing your teeth

If you take a break from PrEP, consider:

Event-based dosing

Event-based dosing (EBD) means you take PrEP around the time of sex.

For receptive or insertive anal, vaginal or frontal sex

EBD works as well as daily dosing for people having anal sex.

It is an option for people who:

  • do not want to take PrEP all the time
  • only have sex without condoms now and again
  • can plan for sex in advance

Transgender women who are taking gender-affirming (feminising) hormone therapy should only use EBD while under the care and supervision of a consultant in sexual health or infectious diseases.

Important

EBD is not suitable if you have hepatitis B - it is very important to know your hepatitis B status before taking PrEP.

EBD for sexual episodes over 1 day

Take 2 tablets (double dose) between 2 and 24 hours before sex. This is to make sure that the medicine levels are high enough to be protective when you have sex.

Take 1 tablet 24 hours after the double dose.

Take a final tablet 48 hours after the double dose.

This is often called ‘PrEP 2-1-1’ or ‘PrEP on demand’.

EBD for sexual episodes over more than 1 day

Use this schedule if you may have sex several times over a period of time. For example, you are away for a weekend or on holidays.

Before sex

Take 2 tablets (double dose) between 2 and 24 hours before sex.

While you are having sex

Take 1 tablet 24 hours after the double dose. Continue taking 1 tablet every 24 hours for the days you are having sex.

After you stop having sex

Take 1 tablet for 2 days after last having sex.

Important

Do not miss any doses if you are taking event-based PrEP.

Missed doses and when to take PEP

If you miss any PrEP doses you may need to take post-exposure prophylaxis (PEP) to reduce the risk of becoming HIV positive.

PEP is a 28-day course of medicine that helps reduce your risk of getting HIV after exposure to the virus.

Post-exposure prophylaxis (PEP)

Missed doses on a daily PrEP schedule

For condomless anal and insertive vaginal or frontal sex

If it has been more than 7 days since your last PrEP dose:

  1. Restart PrEP with 2 tablets (double dose) as soon as possible, preferably within 24 hours and no later than 72 hours after the sexual exposure.
  2. Continue taking 1 tablet a day.
  3. Seek an urgent PEP assessment as soon as possible within 72 hours - whether you have any PrEP medicine or not.

If it has been 7 days or less since your last PrEP dose:

  1. Resume daily PrEP as soon as possible.
  2. If you do not have any PrEP medicine, seek an urgent PEP assessment as soon as possible within 72 hours.

For condomless receptive vaginal or frontal sex

If it has been more than 3 days since your last PrEP dose:

  1. Restart PrEP with 2 tablets (double dose) as soon as possible, preferably within 24 hours and no later than 72 hours after exposure.
  2. Continue taking 1 tablet a day.
  3. Seek an urgent PEP assessment as soon as possible within 72 hours - whether you have any PrEP medicine or not.

If it has been 3 days or less since your last PrEP dose:

  1. Restart PrEP with 2 tablets (double dose) as soon as possible.
  2. Continue taking 1 tablet a day.
  3. Contact your PrEP service.
  4. If you do not have any PrEP medicine, seek an urgent PEP assessment as soon as possible within 72 hours.

For sharing drug-injecting equipment

If it is more than 4 days since your last PrEP dose:

  1. Restart PrEP with 2 tablets (double dose) as soon as possible within 24 hours and no later than 72 hours after the exposure.
  2. Continue taking 1 tablet a day.
  3. Seek an urgent PEP assessment as soon as possible within 72 hours - whether you have any PrEP medicine or not.

If it has been 4 days or less since your last PrEP dose:

  1. Restart PrEP with 2 tablets (double dose) as soon as possible.
  2. Continue taking 1 tablet a day.
  3. Contact your PrEP service.
  4. If you do not have any PrEP medicine, seek an urgent PEP assessment as soon as possible within 72 hours.
Missed doses on an event-based PrEP schedule

EBD for condomless anal sex and insertive vaginal or frontal sex

If you miss the first after-sex dose of event-based PrEP and it’s under 48 hours since exposure (and you took at least 1 tablet before sex):

  1. Take the first after-sex dose.
  2. Take the second after-sex dose 24 hours after the first to complete the course.

If you miss the first after-sex dose of event-based PrEP and it’s more than 48 hours since exposure:

  1. Take the first after-sex dose.
  2. Seek advice about PEP within 24 hours.

If you do not have any PrEP medicine, seek an urgent PEP assessment as soon as possible within 72 hours.

Missed doses and oral sex

If your only exposure has been through oral sex, you will not need to take PEP. This is regardless of how many doses you missed.

Getting PEP urgently

All PrEP services must stock PEP or have access to a service that has PEP, in case you need it urgently.

Where to get PEP

Changing how you take PrEP

You can change how you take PrEP or stop and restart as your circumstances change.

Talk to your healthcare professional if you are taking daily PrEP and want to switch to EBD. They will help you decide if EBD is an option for you. They will help you make the change in schedule safely.

If you are taking EBD and want to switch to daily dosing:

  1. Start with a double dose - take the medicine at least 2 hours and no more than 24 hours before you have sex.
  2. Continue taking PrEP daily.

If you switch from EBD to daily dosing, make sure you have enough medicine to last until your next appointment with your PrEP service.

In some situations, your healthcare professional may suggest switching from daily to EBD to reduce the impact of the PrEP medicine on your kidneys.

Deciding to stop PrEP

PrEP and contraception

It is safe to use PrEP with most hormonal contraception including a ring, patch, pill or implant. PrEP will not affect your contraception and your contraception will not affect PrEP.

PrEP in pregnancy

There are few studies on the use of PrEP in pregnancy. But no PrEP-related pregnancy complications have been identified.

Untreated HIV in pregnant people is linked to a higher risk of transmission to the baby. You may be advised to take PrEP in pregnancy where there is a risk of HIV.

If you are taking PrEP and could become pregnant, talk to your healthcare professional. They can help you make decisions about what is best for you.

PrEP and drug resistance

If you get HIV while taking PrEP, there is a small risk of developing resistance to one or both PrEP medicines. This means the medicine will not work as well against HIV.

PrEP studies have shown that very few people got HIV while taking PrEP. In those who did, fewer than 1 in 20 developed resistance to the medicine.

The possibility of drug resistance increases if you:

  • start PrEP without knowing that you have HIV - always have a laboratory HIV blood test before you start PrEP
  • take a break from PrEP and do not check your HIV status before starting it again
  • do not take PrEP correctly, get HIV and continue to take some PrEP medicine
  • are exposed to drug-resistant HIV - this is very rare

Having a laboratory HIV blood test

Stopping PrEP safely

Tell your healthcare professional if you want to stop taking PrEP.

They can:

  • help you stop PrEP safely
  • organise any tests you may need
  • provide advice on preventing HIV and STIs

You can restart PrEP if your situation changes in the future.

If you stop PrEP and think you may have been exposed to HIV, you may need to take PEP. Take it as soon as possible, and no later than 72 hours after exposure.

Page last reviewed: 26 March 2026
Next review due: 26 March 2029