How and when do I take Pre-Exposure Prophylaxis (PrEP)?
PrEP is a prescription medicine that you can get from a sexual health clinic or from SH.UK (if it’s available in your area). It may not fully protect you against HIV if you don't take it correctly. It's important to take it as advised by your clinic/service.
PrEP comes as tablets. You should take it with food, at any time of the day, but then at the same time every day after that. It still works well on an empty stomach, it’s just that it might cause fewer side effects like nausea or bloating if taken with food.
Depending on how regularly you have sex and what type of sex you have, you can take your tablets in 2 different ways: one pill every day, or two pills before you’re likely to have sex (on demand).
How do I get PrEP online through SH.UK?
SH.UK work with local authorities to provide free sexual health care such as PrEP, home STI test kits & more. Check to see if SH.UK offers PrEP in your area.
If you see the Preventx PrEP image in the list of services we provide then we DO provide PrEP for your area,
If you DO NOT see the Preventx PrEP image in the list of services, we DO NOT currently provide PrEP in your area. You should contact your local sexual health clinic to see how to access PrEP.
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Get PrEP online through SH.UK
SH.UK work with local authorities to provide free sexual health care such as PrEP, home STI test kits & more. Check to see if SH.UK offers PrEP in your area.
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What is Daily PrEP?
Daily PrEP involves taking 1 tabklet each day to provide protection for vaginal/frontal and anal sex.
How to take it
To start we usually recommend taking 2 tablets together (i.e. a double dose) 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.
How do I stop taking daily PrEP?
If you have had anal sex (giving or receiving) or giving vaginal/frontal sex, take your daily dose for 2 more days after the last time you had sex.
If you have received vaginal/frontal sex, take your daily dose for 7 more days after the last time you had sex.
If you have any concerns or questions about stopping check with your clinic/service before stopping.
What is Event-Based or On-Demand PrEP?
Taking PrEP on-demand will give you protection against HIV during anal sex or vaginal/ frontal sex, if you take it correctly. If you are receiving vaginal/ frontal sex then
you need to take it for longer than if giving vaginal/ frontal sex or having anal sex, see below.
On-demand PrEP is useful if you can plan when you have sex and/ or don’t have sex frequently.
How to take PrEP on demand
Anal sex (giving or receiving) or giving vaginal/ frontal sex:
- Take 2 tablets (double dose) between 2 and 24 hours before having sex
- take 1 tablet 24 hours later
- take 1 tablet 24 hours after that
If you're continuing to have sex over several days, carry on taking 1 pill every 24 hours until you have not had sex for 2 days.
Receiving vaginal/ frontal sex:
- Take 2 tablets (double dose) between 2 and 24 hours before having sex
- Take 1 tablet 24 hours later
- Take 1 tablet 24 hours after that and repeat until you’ve taken it for 7 full days after the last time you had sex.
- If you're continuing to have sex over a few days, carry on taking 1 pill every 24 hours until you have not had sex for 7 days.
How do I stop on-demand PrEP?
If you’ve had anal sex or give vaginal/ frontal sex, take your daily dose for 2 more days after the last time you had sex. It's then okay to stop.
If you have received vaginal/frontal sex, take your daily dose for 7 more days after the last time you had sex.
Stopping taking this medicine too early or missing doses may increase your risk of getting HIV infection.
What if I forget to take PrEP tablet(s)?
Daily
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 okay. 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, contact your clinic/service 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.
Event-based/ on-demand
It is very important that you take a double dose of PrEP between 2-24 prior to sexual activity; a single table each day you are having sex; and a single tablet for either 2 days (for anal and giving vaginal/ frontal) or 7 days (for receiving vaginal/ frontal) after the last time you had sex for on-demand PrEP to be effective.
If you forget a PrEP tablet when taking on-demand, contact your clinic/ service for advice.
Help remembering to take doses
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.
I have problems swallowing PrEP tablets
If you find swallowing tablets difficult, you can crush the PrEP tablet and mix it with a drink of water, orange juice, grape juice or something like yoghurt.
What if I vomit after taking my PrEP tablet?
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, you don’t need to take another tablet.
How long do I take PrEP for to be protected?
If you take a double dose (i.e. 2 tablets) as single dose you will be protected after 2 hours, if you continue to take PrEP as discussed in the Daily and On-Demand dosing sections.
If you prefer not to have double doses, you need to take 1 tablet each for 7 days before you are protected.
To stay protected on daily dosing, you must have taken at least 6 doses in the past week to still be protected.
If you stop taking PrEP you will no longer be protected from HIV.
If your HIV risk changes, you can stop or restart PrEP, or change the way you take it. If you are not sure how to do this contact your clinic/ service.
How long can I take PrEP for?
As long as you have regular tests, you can take PrEP for a long time.
What tests do I need to do before taking PrEP?
Before you start taking PrEP, you'll be asked to:
- test for HIV and other STIs – you'll need to continue to have these regularly, for example, every 3 months.
- take a Hepatitis B test – to confirm you do not have a Hepatitis B infection. Ideally you should get vaccinated against this too if you have not been vaccinated before or not up to date with your vaccinations.
- take 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/service. If there are any concerns about your blood test results, we may talk to you about stopping PrEP treatment.
I find it hard to do my own blood, can I use the SH.UK PrEP service?
To use the digital SH.UK PrEP service you do need to be able to provide a self-sampled blood test. We need these results to start and monitor you while on PrEP.
We have lots of advice on our website on how to take blood [Finger Prick Blood Test Kit | How to take your sample — SH.UK]. If you initially feel uneasy, we advise you give it a go and see how you get on. You usually find it gets easier the more you do it.
If you really cannot provide a home blood sample, we would not be able to provide digital/ remote PrEP for you. In these cases, we recommend you attend your local sexual health clinic to access PrEP.
Why do I need to test for HIV to use this service?
PrEP is not suitable for people living with HIV. This is because the medication uses 2 of the antiviral drugs used to treat people with HIV positive (along with other medications). A third drug is usually needed so taking them alone could make HIV treatment less effective.
Can I take PrEP if I have Hepatitis B
We don’t recommend using on-demand dosing if you have Hepatitis B because PrEP can affect the Hepatitis B virus. Starting and stopping PrEP can make the Hepatitis B virus more active and this can lead to liver inflammation. If you have current active Hepatitis B infection, we recommend attending your local sexual health clinic to explore your PrEP options and ensure you are monitored correctly.
Can PrEP make me loose or gain weight?
You may experience slight weight loss, or a slight weight increase.
Try to eat well without increasing your portion sizes. Regular exercise will also help to keep your weight stable. If you start to have problems with your weight while taking PrEP, talk to your clinic/service for advice.
Will PrEP affect my contraception?
PrEP does not affect any type of contraception, including the combined pill or Emergency contraception - NHS (www.nhs.uk).
However, if PrEP makes you sick (vomit) or have severe diarrhoea for more than 24 hours, your contraceptive pills may not protect you from pregnancy. Check the pill packet to find out what to do.
Find out more about what to do if you're on the pill and you're being sick or have diarrhoea.
Will PrEP affect my ability to drive or ride a bike?
PrEP can make you feel dizzy for the first few weeks of taking it. Don’t drive a car, ride a bike or use tools or machinery if this happens to you.
It's an offence to drive a car if your ability to drive safely is affected. It's your responsibility to decide if it's safe to drive. If you're in any doubt, don’t drive.
Talk to your clinic/service if you're unsure whether it's safe for you to drive while taking PrEP. GOV.UK has more information on the law on drugs and driving.
Can I drink alcohol with PrEP?
Yes, you can drink alcohol while taking PrEP.
Is there any food or drink I need to avoid with PrEP?
You can eat and drink the way you usually would while taking PrEP.
Will recreational drugs affect PrEP?
Taking PrEP can make recreational drugs affect you differently, especially if you have just started taking PrEP.
When you start taking PrEP it takes time for your body to get used to it. If you take recreational drugs during this time, it can increase the risk of side effects.
If you’re using recreational drugs, tell your clinic/service so they can explain the risks.
Find out more about the side effects of recreational drugs on the Frank website.
Can I take PrEP with other medicines?
PrEP does not interact with most other medicines.
PrEP doesn’t interact with alcohol or recreational drugs. It is safe to take with hormonal contraceptives and most over-the-counter medicines. PrEP is safe for trans people taking hormones.
Is there any issues taking PrEP if I have problems with my kidneys?
Tenofovir disoproxil fumarate (one of the drugs in Truvada and its generic formulations – the ones SH.UK use for PrEP) may interact with other medicines associated with kidney problems. If you have long-term health conditions or are using other medicines, talk with your clinic/service before starting PrEP.
If you develop kidney problems, have new medical conditions and start new medications while on PrEP check in with the clinical team to make sure this won’t affect your PrEP.
Are there side effects from taking PrEP?
Most people who take PrEP experience no side effects.
There are, however, some short-term side effects that have been reported by some people who use PrEP.
Studies show 1 in 10 people report short-term side effects. These can include feeling sick, stomach pain, dizziness and headache. These tend to be most common in the first month of using PrEP. For most people these side effects last for a few days and almost always stop within a month.
If you experience any side effects that last longer than this, it’s worth having a chat with your health service as they may be able to prescribe medication that can help.
Does PrEP prevent pregnancy?
PrEP does not prevent pregnancy, so you’ll need to think about contraception if you don’t want to become pregnant while using PrEP. PrEP is safe to use with hormonal birth control and when you are trying to conceive. PrEP can also be used safely during pregnancy.
Can PrEP prevent other STIs?
PrEP prevents HIV but will not protect you from other sexually transmitted infections (STIs) like chlamydia, gonorrhoea, syphilis or genital herpes, so you should use other methods of protection such as condoms. You should also get vaccinated against HPV and hepatitis B and A at your local sexual health clinic.
You may want to test for other STIs regularly as some STIs don’t have any symptoms.
Can PrEP be used as PEP?
You can’t use PrEP as PEP. PEP stands for ‘post exposure prophylaxis’, and it’s not the same as PrEP.
PEP is a course of medicines you take soon after sex if you think you’ve been exposed to HIV. It’s usually prescribed for a month and should be taken immediately after you think you have been exposed to protect you from the virus.
If you think you’ve been exposed, visit your local sexual health clinic, GP, or A&E department immediately, as you may be able to take PEP if it’s within 72 hours of possible infection.
Where can I find more information about using the SH.UK PrEP service?
To find out more information about the SH.UK PrEP service please visit our webpage: How SH.UK's PrEP service works — SH.UK
Reviewed by Adam Black on 29th Jan 2025.