PrEP for HIV: UK guide

This page answers questions about HIV PrEP.

What is PrEP?
Changes in 2025
Getting PrEP in the UK
Who can take PrEP?
How well does PrEP work?
PrEP and side effects
PrEP and drug resistance
PrEP and sexually transmitted infections (STIs)
Does PrEP interact with other medicines?
PrEP for women
PrEP for trans and non-binary people
PrEP and work
Buying PrEP in the UK
Before you start PrEP
Monitoring on PrEP
How to start and stop oral PrEP
TAF and TD
Daily oral PrEP
Event-based PrEP (2:1:1 and 2:7 dosing)
Event-based oral 2:1:1 PrEP: sex once
Event-based 2:1:1 dosing: more sex!
Event-based 2:7 dosing (first week)
Tips on taking oral PrEP
Can I switch between daily and event-based dosing?
Is PEP recommended if I am on PrEP?
Can I stop PrEP completely?
Credits

1. What is PrEP, PEP and doxyPEP?

PrEP stands for Pre-Exposure Prophylaxis.

PrEP is taken before sex, so it is pre-exposure. But it also needs to be taken afterwards too. Prophylaxis means to prevent something.

Last year, more than 110,000 people in the UK used oral PrEP.

Oral PrEP contains two HIV drugs in a single pill. This is usually TD (tenofovir disoproxil) plus FTC. A version using TAF (tenofovir alafenamide) instead of TD is only used if you have kidney or bone issues. Generic TAF/FTC can also be bought cheaply online, see below.

There are two injectable versions of PrEP. Cabotegravir (CAB-LA) is a two-monthly injection for people who can’t take pills. Lenacapavir is a 6-monthly injection that is only available in the UK in the PURPOSE 5 study, which is still recruiting.

PEP and doxyPEP

PrEP is different to HIV PEP. [3]

PEP involves taking one month of HIV drugs AFTER unprotected sex to reduce the chance of HIV. HIV PEP can only be used by people who are HIV negative.

DoxyPEP involves taking a single dose of the antibiotic doxycycline after sex to reduce the chance of syphilis and chlamydia. New guidelines on doxyPEP in the UK were published in June 2025. [4]

DoxyPEP can be used by anyone at risk of these STIs. This includes people who are HIV positive or HIV negative.

In August 2025, a vaccine to prevent gonorrhoea became available in the UK.. [5]

2. Changes in 2025

Everyone who can benefit from PrEP in the UK should now be able to get it free on the NHS.
Start oral PrEP with a double first dose (two pills). This gives full protection after two hours.
Event-based dosing can also now be used by everyone. This uses either 2:1:1 or 2:7 dosing.
Everyone taking at least four daily doses a week will get good protection.
Both versions of oral PrEP can be used in the same ways (ie TD/FTC and TAF/FTC).
There is new info on injectable PrEP and doxyPEP.

Changes based on latest BASHH guidelines (www.bashh.org).

3. Getting oral and injectable PrEP in the UK

Oral PrEP is now available free from sexual health clinics across the UK. It can also still be bought online.

These sites have more information, including on how to find a sexual health clinic by postcode.

Scotland: www.prep.scot

Wales: www.shwales.online/wales-prep-project.html

Northern Ireland: www.rainbow-project.org/prep

England: www.nhs.uk/nhs-services/sexual-health-services/find-a-sexual-health-clinic/

If a clinic does not want to prescribe you PrEP, please ask them why. They should explain this. Or they might not know about the new UK guidelines.

If you still cannot access PrEP, ask to speak to a more senior health worker or clinic manager.

See also: information about buying PrEP online from the UK.

Injectable PrEP using cabotegravir-LA (CAB-LA) was approved in England and Wales in October 2025 and in Scotland slightly earlier. This is only for about 1000 people each year who are not able to use oral PrEP. CAB-LA is given by an injection into your buttock muscles every two months. Access is likely to become available from January 2026 onwards. Few details have been released about access yet.

Injectable PrEP using lenacapavir is not yet approved in the UK. It will be submitted to the UK medicines agency (called the MHRA) by the end of 2025. It is likely to then take another year before the NHS is able to prescribe it. Lenacapavir PrEP involves two injections given under the skin every six months.

4. Who can take PrEP?

2025 guidelines say that anyone who is HIV negative and who could benefit from PrEP should be able to access it.

For example, if you have used PEP or had a recent STI. Or if you have chemsex or have partners with these risks.

You do not need PrEP if…

You are happy and able to always use condoms.
You only have sex with people who have an undetectable viral load and are taking HIV treatment.
You don’t use condoms but your partner is low risk.

5. How well does PrEP work?

PrEP is more than 99% effective.

Very few people become HIV positive when taking PrEP as prescribed.

Rare cases of transmission are often because HIV was missed in the pre-test. Recent HIV is not always detected. Having another HIV test six weeks after either the most recent risk or after starting PrEP can pick this up.

A few cases are because of HIV drug resistance.

6. PrEP and side effects

Most people taking PrEP do not get side effects.

However, like all medicines, some people might get some side effects. Less than 1 in 10 people report mild nausea, diarrhoea, bloating and headache. These side effects then usually stop.

Taking oral PrEP with food can help. It is also okay to separate the first double dose by a few hours. Monitoring tests pick up more serious side effects such as kidney problems with oral TD/TFC.

Changes in bone structure with TD/FTC are usually small and reverse after stopping. This is similar to a commonly used oral contraceptive but might be important if you are younger than 18 when bones are still developing. Bone strength was not fully reversed after a year in an adolescent study and people aged 18 or younger can use TAF/FTC instead.

PrEP does not increase the risk of bone fractures.

Injection site reactions are common with injectable PrEP.

7. PrEP and drug resistance

The chance of drug resistance to PrEP is very low.

Resistance also relates to the virus and not the person. So an HIV negative person can’t be drug resistant.

Drug resistance occurs in two different ways, both rare.

(i) Drug resistance that develops while taking PrEP.

Taking PrEP if you are HIV positive will lead to HIV developing drug resistance. This is why you need an HIV test first – and sometimes also after six weeks.
Becoming HIV positive during a break from PrEP and not re-testing before starting again.
Missing too many PrEP doses leads to drug levels are too low to protect you.

(ii) If you come into contact with drug-resistant HIV.

In this case the drug resistance will stop PrEP from working.
Very few cases have been reported of PrEP not working because of drug-resistant HIV.

8. PrEP and sexually transmitted infections (STIs)

PrEP does not protect against other STIs. Condoms can help prevent many of these though.

Although STIs are mostly easy to treat, symptoms can be unpleasant and sometimes serious. Regular STI testing is good advice. DoxyPEP* is also now available in the UK.

The HPV vaccine reduces the risk of genital warts and cervical and anal cancers. Please ask your clinic or GP about this.

Your clinic should also provide vaccines for hepatitis A and B if needed, for mpox and now for gonorrhoea.

*DoxyPEP is a way to reduce the risk of syphylis and chlamydia by taking an antibiotic after sex. DoxyPEP involves taking 200 mg doxycycline (as 2 x 100 mg pills) within 24 to 72 hours of having sex.

UK doxyPEP guidelines

9. Does PrEP interact with food or other meds?

Oral PrEP is just as effective whether it is taken with or without food.

However, TD is absorbed more quickly if it is taken with food and so this could be used if you are late with your dose.

Oral PrEP only interacts with a few other medicines, covered below.

But if you routinely take other prescribed or over-the-counter meds, please tell your doctor (including your GP) that you are taking PrEP. Any pharmacist can also check for drug interactions if you don’t want your GP to know.

Tenofovir (TD) should also be used with caution if you regularly take other drugs that affect the kidneys. These include some non-steroidal anti-inflammatory drugs (NSAIDs), especially diclofenac, ibuprofen and naproxen.

Routinely taking these drugs with PrEP can cause kidney problems. Avoid these meds when taking PrEP and please let your doctor know if you regularly need to take them.

TAF can interact with TB meds, anti-epileptics, St John’s Wort and others. These interactions are not a problem with TD.

It is easy to check for interactions here:

hiv-druginteractions.org/checker

This factsheet covers drug interactions between about 85 other medications where there are cautions about long-term use with oral PrEP.
www.hiv-druginteractions.org/prescribing_resources/hiv-guidance-prep

For trans and non-binary people

Oral PrEP is very safe for trans and non-binary people taking hormone therapy.

Info on interactions between PrEP and other meds, including hormone treatment, is on this site from Liverpool University:

hiv-druginteractions.org/checker

Injectable PrEP

Injectable PrEP can also be taken with or without food.

There are no interactions with oral contraceptives or with gender affirming hormones that need a dose adjustment.

These drugs can interact with different other meds though.

Because these drugs stay in your body for such a long time, interactions can continue for a long time after the last injection. Please see the full prescribing information for details of these and other interactions.

Please tell your doctor or pharmacist about any other drugs or supplements that you take. Drug interactions can also be checked using the online checker at Liverpool University HIV Interaction website:
https://www.hiv-druginteractions.org/checker

CAB-LA can interact with:

Carbamazepine, oxcarbazepine, phenobarbital, phenytoin (medicines for epilepsy).
Rifabutin, rifampicin, rifapentine (antibiotics).
Systemic dexamethasone (a steroid anti-inflammatory and immunosuppressant medicine), except when used as a single dose treatment.
St John’s wort (a herbal antidepressant medicine).

LEN interactions:

The following should NOT be taken with LEN as they reduce LEN levels:

Some HIV meds: efavirenz, etravirine, nevirapine, atazanavir/cobicistat, and tipranavir/ritonavir.
Some TB meds: rifampicin, rifabutin.
Some anticonvulsants: carbamazepine, phenytoin, oxcarbazepine and phenobarbital.
Some herbal supplements: St. John’s wort.

The following drugs can be increased by LEN. They can sometimes be used at lower doses.

Some PDE-5 erectile drugs: sildenafil (Viagra), taladafil, vardenafil.
Ergot derivatives: dihydroergotamine and ergotamine.
Some corticosteroids: dexamethasone hydrocortisone/cortisone.
Some other drugs: dioxin, midazolam, triazolam, lovastatin and simvastatin.

10. PrEP for women

Why should women take PrEP?

PrEP can be used by anyone worried about the risk of HIV.
PrEP is a very effective way to stay HIV negative.

The highest risk of getting HIV is if you don’t always use condoms with partners who do not know that they might be HIV positive.

Or if a partner is not yet on HIV treatment (ART) or is not always taking their meds.

People living with HIV cannot pass on HIV if they have an undetectable viral load on ART.

Other reasons to consider PrEP

If you are worried about HIV.
If condom use is difficult or impossible to negotiate.
If you have sex for money, or receive gifts for sex.
If your partner or partners might be at risk of HIV. For example, if your partner has other partners. Or if you or your partner(s) inject drugs and share injecting equipment.

Oral dosing for women

The 2025 guidelines include new information about how women can take PrEP.

This includes:

Starting PrEP with a double dose (two pills) to become protected after only two hours.
Taking at least four doses a week will give high levels of protection.
Event-based dosing is now possible. Start with a double dose. Then take a single pill every day for seven days after you last had sex. This is called 2:7 dosing.
Although modelling studies show that three daily doses after sex should be enough – ie 2:1:1:1 – this is not included in guidelines. UK guidelines do note that 2:7 is a cautious approach.
Oral PrEP can also be taken every day if you want to do this.

Please see these links.

Injectable PrEP

CAB-LA

In October 2025, following NHS Scotland, NHS England approved limited access to injectable cabotegravir-LA (CAB-LA).

This is a long-acting version of PrEP that is given by injection every two months. It is a very effective way to use PrEP if you have difficulty taking pills.

The injections need to be given by a health worker into your buttock muscle.

Access to CAB-LA should start by January 2026. Please talk to your clinic to find out more information.

LENACAPAVIR

Lenacapavir (LEN) is another type of injectable PrEP which only needs to be given as two injections every six months.

It also needs to be given by a health worker but the injections are under the skin, usually on your choice of stomach, thigh or abdomen.

LEN PrEP is already approved in Europe and the US but has not yet been submitted to the UK medicines agency. This is expected before the end of 2025. This means it will not be available in the UK for at least another year.

Currently LEN PrEP is only available in the UK as part of the PURPOSE 5 study.

Contraception

It is very safe to use PrEP with all hormonal contraception (ring, patch, the pill, injectable or an implant).

PrEP will not affect your contraception. And contraception will not affect PrEP.

Pregnancy

If planning a pregnancy and not using barrier protection or condoms, daily PrEP can protect you from HIV.

But if you know that your partner is HIV positive, it is better for them to be on HIV treatment. If their viral load is undetectable, this will also protect you from HIV.

If you become pregnant while taking PrEP, continuing PrEP is still recommended but please also talk to your doctor.

Breastfeeding and chestfeeding

Oral PrEP is very safe if you breastfeed or chestfeed.

Outside the UK, many people living with HIV use the same meds as HIV treatment during breast and chest feeding.

Only very small amounts of FTC and TD are present in breast milk. These low levels are not harmful to your baby.

UK community websites on women and PrEP

PrEP for Women leaflets and translations

A separate leaflet was developed by Women for PrEP and the Sophia Forum. It is also available in the following languages as PDF files to download or view online.

However, they have not yet been updated to include the latest information on dosing.

English PDF
Shona PDF
Spanish PDF
Swahili PDF
Xhosa PDF
French PDF (via Sophia Forum)
Portuguese PDF (via Sophia Forum)

For French and Portuguese printed leaflets, please contact Women for PrEP.

11. PrEP for trans and non-binary people

PrEP is just as safe and effective whether you are transgender, non-binary or cisgender.

This is the case for both oral and injectable PrEP.

Dosing choices for oral depend on the type of sex, although daily dosing has generally been recommended.

Everyone can start PrEP with a double dose (two pills). This works in two hours rather than the old advice to take daily PrEP for 7 days before sex.

After sex, take daily PrEP (one pill) for seven days if you want to use event-based dosing (called 2:7). If you want to continue on daily PrEP, you just need to take at least 4 daily doses each week.

Anyone having insertive or receptive anal sex or insertive vaginal/frontal sex can use 2:1:1 event-based dosing. Event-based dosing using 2:7 dosing is recommended for receptive vaginal/frontal sex.

Note: Some researchers think that 2:7 dosing is too cautious and that fewer doses after sex would be okay, for example, 2:1:1:1 dosing. This is based on limited data though and isn’t included in guidelines.

Please see these links.

PrEP is very safe with hormone treatment

Even though you might worry about drug interactions, neither your hormone or PrEP levels will be affected.

Liverpool University produces an excellent guide to drug interactions between hormone treatments and other HIV meds:

hiv-druginteractions.org/printable_charts

Ongoing studies are looking at other aspects of PrEP in trans women and men.

Useful links

CliniQ

CliniQ is a London-based specialist clinic providing sexual health and well-being services for trans people.

56T clinic

56T clinic at Dean Street has a very busy PrEP service for trans and non-binary people.

Clinic T

Clinic T is a trans and non-binary friendly sexual health service in Brighton.

Indigo Gender Service

Indigo Gender Service is an NHS trans healthcare service in Manchester.

12. PrEP and work

PrEP can be used for any job in the sex industry including porn.

Many sex workers look after their sexual health but their clients might not. PrEP will protect against HIV if you are pressured to not use condoms. Use specialised services that are free from stigma and judgement. See: www.uglymugs.org

Back to top

13. Buying PrEP in the UK

It is legal to buy oral PrEP online for personal use.

This is defined as up to three months of daily PrEP.

Prices for online TD/FTC range from about £20 to £40 + post for 30 tablets. TAF/FTC is similar or a little more expensive.

Generic PrEP contains the same meds as brand products but is made by different companies. For example, TD/FTC from NHS clinics will always be generic.

Buying oral PrEP online might take a while for the drugs to arrive. It is best to order at least a month in advance.

You need a combined pill that contains both tenofovir (TD, TDF or TAF) and FTC (emtricitabine). For example, you need Tenvir-EM or Ricovir-EM rather than just Tenvir or Ricovir.

The NHS is only responsible for meds that it supplies but some clinics might help with advice. See also these community links:

14. Before you start PrEP

First, please talk to a health adviser, nurse, doctor or community worker. These people can help you if you want to start PrEP, or are already taking it.

Then you need an HIV test before or as you start.

If you are already HIV positive and don’t realise it, you could develop drug resistance.

Ask for a 4th generation HIV blood test. This is also called an antigen/antibody test. This can not tell you about any risks in the last six weeks.

Most finger prick tests are 3rd generation. This test needs 2-3 months to show a positive result. Don’t rely on a finger prick test before PrEP if you have a more recent risk.

If you are just starting PrEP and had a risk in the last six weeks, have another 4th generation HIV test six weeks after starting. This is to be sure an early infection is not missed.

Be careful about starting PrEP if you have flu-like symptoms and had a recent HIV risk. This is in case these symptoms are related to a recent HIV infection.

If you are starting PrEP after PEP, it is best to start straight away if you need to. Ideally you should have a 4th generation HIV test after you finish PEP/start PrEP. Then have another test six weeks after starting PrEP.

Check your kidneys

A kidney test just involves a blood test for creatinine. This should ideally be done just before or on the day you start. Some clinics might still test for protein in a urine sample.

Check for other sexually transmitted infections (STIs)

Testing for HIV and STIs is a great idea for anyone with an active sex life. This is whether you use PrEP or not.

Hepatitis B (hep B, HBV)

Testing for hep B is essential. This is because PrEP meds are active against both HIV and HBV.

This is a good time to have this vaccine, or to boost a previous vaccine. Please ask your clinic about this.

People with hep B need to take daily PrEP, with medical advice, especially if you want to stop.

Stopping PrEP can lead to rapid inflammation in the liver.

This can be very serious. It can lead to hospitalisation and in rare cases can be fatal.

15. Monitoring on PrEP

Once you have started PrEP, monitoring is important.

If you are currently using PrEP and have not been monitored, please talk to the clinic about doing this now.

Every 3-4 months

Have a 4th generation HIV blood test. This is also called an antigen/antibody (Ag/Ab) HIV blood test.
Have a full screen for other STIs.
Oral PrEP sometimes needs an additional blood test for kidney function (creatinine) every six months or more often. This is if you are older than 40 or are at risk of kidney problems.
Some clinics are now happy to alternate quarterly monitoring between clinic visits and self-sampling postal kits.
Some clinics might arrange for six-monthly prescriptions for oral PrEP.

Every 12 months

Have a blood test to check your kidney function.
Test for hepatitis C if you are having sex with gay men. Some clinics do this more frequently depending on risk.

Testing might also be individualised if you are not having sex very often.

For trans and non-binary people

There are no drug interactions between PrEP and hormone treatment. Neither PrEP nor hormone levels are affected. If you are worried about PrEP please speak to your doctor who can also reassure you.

16. How to start and stop oral PrEP

Starting oral PrEP

Everyone is now recommended to start oral PrEP using a double dose (two pills) for the first dose BEFORE sex.

This gives protection within two hours.

Continuing oral PrEP

Daily dosing then involves continuing with a single pill every day at roughly the same time.

For daily PrEP, current guidelines recommend at least four daily doses a week.

But if you stop PrEP for a week, please restart using a double dose and take seven daily post-sex doses that week.

Stopping oral PrEP

If you are using event-based dosing, continue daily dosing for either another two days (2:1:1 dosing) or seven days (2:7 dosing).

Before stopping daily dosing, please continue for either two or seven days after you last had sex. This depends on how you are dosing PrEP. Please see:

Daily PrEP dosing

Stopping injectable PrEP

Special advice is needed if you decide to stop injectable PrEP.

This is because of how long these drugs stay in your body. In theory, if for any reason you become HIV positive after stopping PrEP injections, the virus might develop resistance to the PrEP meds.

Changing to oral PrEP if you continue to be at risk of HIV will prevent drug resistance.

This is important to know about even if you are stopping PrEP because you are no longer at risk.

17. TAF and TD

TAF/FTC can be dosed the same way as TD/FTC.

Even though there is less evidence for vaginal and neovaginal sex, this should still be okay.

This is because PrEP efficacy is no longer thought to be linked to drug levels in different tissues, but to drug levels in cells called PBMCs.

18. Daily oral PrEP

Most PrEP studies used daily PrEP.

Taking PrEP every day makes sure that there are protective drug levels 24 hours a day, 7 days a week, even if you don’t have sex. This means you can have sex any time, without planning for PrEP.

If you have sex every week, daily PrEP might be an easier routine. After the first week, this just needs at least four daily doses each week.

Quick-start daily dosing using a double dose (two pills) for the first dose. This will protect you after two hours. The pre-dose is important for the highest protection.
If you miss or are late with the pre-dose, start with a double dose as soon as possible. Taking PrEP with food can boost drug levels of TD more quickly.
Once on PrEP, continue taking daily PrEP for at least four days each week.
There is currently no data about neovaginal sex. Starting with a double dose and then using daily dosing is currently recommended. This double dose before sex gives everyone very high protection.

19. Event-based PrEP (2:1:1 and 2:7 dosing)

Event-based dosing involves only using oral PrEP when you want to have sex. It is also sometimes called on-demand dosing.

Start with a double dose (two pills) at least two hours before you are going to have sex. However, instead of continuing to take daily PrEP you only continue for either two or seven days – depending on the type of sex you have.

Event-based dosing is just as effective as daily PrEP. It is often used by people who have sex less often than once a week and who usually know when they might be likely to have sex.

Event-based dosing needs fewer pills, but it can’t be used if you have hepatitis B.

2:1:1 dosing involves starting with a double dose and then taking daily PrEP for two days after sex. Each dose should be roughly 24 hours after the previous one.

2:1:1 dosing can be used by anyone for anal sex (if you are the insertive or receptive partner) or insertive vaginal/frontal sex. It can not be used for receptive vaginal/frontal sex.

2:7 dosing involves starting with a double dose and then taking daily PrEP for seven days after sex. Each dose should be roughly 24 hours after the previous one.

2:7 dosing needs to be used by cis women and trans and non-binary people who are having receptive vaginal/frontal sex.

The pre-dose is important for the highest protection when using event-based dosing. But if you miss or are late with the pre-dose, start with a double dose as soon as you can.

Taking PrEP with food can boost levels of TD more quickly.

20. Event-based oral 2:1:1 PrEP: sex once

2:1:1 dosing can be used by anyone having insertive sex or receptive anal sex.

If you might have sex on Thursday take a double dose at least two hours before you have sex.

Then take a single pill for the next two days. This should be roughly 24 hours and 48 hours after the first double dose.

These times can be approximate. You still get good protection even if you have sex earlier or later than planned. Even if the pre-dose is only just before or even after sex, some PrEP is always better than none.

If you have sex several times over a few days, keep taking a pill each day. Continue for two days after the last day that you have sex.

21. Event-based 2:1:1 dosing: more sex!

If you have sex over a few days, keep taking a pill each day. Continue for two days after the last day you have sex.

If you have sex over several days continue to take a single pill every day you have sex at around the same time.

Then after you stop having sex, take daily PrEP for the next two days.

If you start PrEP but then don’t have sex – and you have no plans to have sex – there is no need to keep taking PrEP.

22. Event-based 2:7 dosing (first week)

2:7 dosing is sometimes needed by cis women and trans and non-binary people having receptive vaginal/frontal sex.

If you are a cisgender woman or are a transgender or non-binary person having receptive vaginal or frontal sex, please continue daily PrEP for seven days.

This is for situations when you didn’t take at least four doses of PrEP the previous week.

Start with a double dose before sex and then take daily PrEP for seven days after sex, at roughly the same time each day.

23. Tips on taking oral PrEP

A pill box makes it easy to see whether you have taken or missed a dose. They only cost £1 or so from a pharmacy.
Pick a regular time and try to stick to this each day. Link it to a routine task like brushing your teeth. It doesn’t have to be the exact same time but it will help you get into a routine.
If you have a break from PrEP and have risks during this time, it is important to have another HIV test.
With on-demand dosing, if you miss the BEFORE dose completely, still take a double dose AFTER sex, and continue daily. Contact your clinic in case PEP is recommended. Missed doses matter more if you are using on-demand rather than daily dosing.

What to do if you miss a pill on daily PrEP

If you are taking daily PrEP, then do not worry if you sometimes miss one or two pills.

Everyone taking daily PrEP will get good protection so long as you take at least four pills every week.

What to do if you miss a pill on event-based PrEP

Event-based dosing needs all the doses.

If you are late or miss a pill, just take it as soon as you remember and then continue as recommended.

Drug levels will still be high enough to protect against HIV. If you often miss doses perhaps it would be better for you to use daily dosing.

Taking a late dose with food can boost drug levels more quickly.

A pill box makes it easy to see if you missed a dose.
Aim for the same time each day. Link it to a routine task like brushing your teeth.
If you have risks during a break from PrEP, remember to have another HIV test.
With event-based dosing, if you miss the BEFORE dose, still take a double dose asap AFTER sex, and continue single daily doses. Contact your clinic in case PEP is recommended.

24. Can I switch between daily and event-based dosing?

PrEP dosing is very easy to change.

PrEP can adapt to your needs at different times. You can stop and restart PrEP, or change the way you take it.

Please talk to your clinic about ways to take PrEP and about how to stop or restart when you need to.

See above about daily and event-based dosing.

PrEP and hepatitis B

Everyone who has active hepatitis B needs to take PrEP every day and not miss doses.

This is because PrEP is also treating hep B and keeping it under control.

Stopping PrEP can lead to rapid inflammation in the liver.

This can be very serious. It can lead to hospitalisation and in rare cases can be fatal.

25. Is PEP recommended if I am on PrEP?

PEP stands for post-exposure prophylaxis and involves taking a combination of three HIV meds for one month.

If you need PEP, the earlier you start, the more likely it is to work.

i-base.info/qa/factsheets/pep-faq

PEP is most effective if started within 24 hours.

In the UK, PEP can be started up to 72 hours after sex.

There is no benefit from using PEP after more than 72 hours.

If you have a risk when you haven’t been taking PrEP, or enough PrEP, please contact a doctor to talk about whether you might need PEP.
Take a double dose of PrEP asap (if you still have some). This will cover you while you are trying to access PEP.
You can get PEP from your clinic or from A&E when your clinic is closed. A&E departments are open 24 hours a day, 7 days a week.

26. Can I stop PrEP completely?

Yes, it is easy to stop PrEP.

Please discuss this with your clinic.

You might want to discuss this with your partner(s) and get tested for HIV and other STIs together. Use a 4th generation HIV test six weeks after the last time you had sex.

How you stop PrEP depends on how you were taking PrEP.

If you were taking daily PrEP, then continue for seven days.

If you were using event-based dosing then stop after your last planned dose. This will be after two days with 2:1:1 dosing or seven days with 2:7 dosing.

It is always easy to restart PrEP in the future if your circumstances change again.

If you stop PrEP and have a risk afterwards, please contact your clinic. This is in case you need post-exposure prophylaxis (PEP). Outside of clinic hours, please contact A&E.

PEP needs to be started as soon as possible (see p22).

i-base.info/qa/factsheets/pep-faq

27. Credits

Written by Dan Clutterbuck, Simon Collins, Sheena McCormack, Achyuta Nori, Will Nutland, Greg Owen, Mags Portman*, Michelle Ross, Sophie Strachan, Martina Toby, Laura Waters, Ashwin Caffery and Aedan Wolton. Cover graphic: iwantPrEPnow.co.uk.

*This guide is dedicated to our inspirational co-author Dr Mags Portman who was a leading advocate for PrEP in the UK. Mags died from mesothelioma in February 2019 aged 44 and we miss her deeply.

Thanks to the London Borough of Lambeth for support with this resource.

ISSN 2398-6409 (i-Base, London, 13th edition, November 2025).

Last updated: 6 November 2025.