PrEP (Pre-Exposure Prophylaxis) for HIV

What is PrEP?

PrEP is a way of preventing people who are HIV-negative from acquiring HIV infection by taking a pill containing two anti-HIV drugs, emtricitabine and tenofovir disoproxil.

If the person taking PrEP is exposed to HIV, the anti-HIV drugs in their body stop the virus from entering cells and replicating. This prevents HIV from establishing itself and stops the virus from taking hold.

How effective is PrEP?

Research shows that PrEP is very effective at preventing the sexual transmission of HIV, as long as it’s taken correctly. It works for people of all genders, including transgender and those who identify as non-binary people.

However, PrEP does not protect against other sexually transmitted infections (STIs) like gonorrhoea, chlamydia, syphilis or hepatitis C, and it does not prevent pregnancy.

PrEP is different from post-exposure prophylaxis (PEP):

PEP is taken after a possible exposure to HIV and is used for 28 days.
PrEP is taken before sex on an ongoing basis.

Both are used to help prevent HIV infection.

Who is PrEP suitable for?

PrEP is not the right choice for everyone. It is most likely to benefit those who are at higher risk of HIV infection, for example:

• Men who have sex with men (MSM)

• Trans men and women

• People with partners from parts of the world where the rate of HIV is much higher

• People with an HIV positive partner who does not have an undetectable viral load

• People who do not always use condoms for sex.

You do not need to take PrEP if:

• you consistently use condoms and other HIV prevention strategies

• your partner definitely does not have HIV

• your partner is living with HIV but taking HIV treatment and has an undetectable viral load

PrEP may not be right for you if it’s hard to take the pills without missing any, or you can’t visit the clinic for regular medical appointments.

How to take PrEP

PrEP can be taken with or after food. If you find it difficult to swallow the tablet, you can mix it into approximately 100ml of water, orange juice or grape juice and drink it straight away.

If you are sick within 1 hour of taking PrEP, you should take another tablet.
If you are sick more than 1 hour after taking PrEP, do not take a second tablet.

PrEP can be taken either regularly or ‘on demand’/'event-based'. How you take it depends on your circumstances and how often you have sex. Your clinician will discuss the various options with you and advise on the most appropriate dosing for you.

Types of dosing

Regular dosing

Regular dosing is more suitable for people who are at ongoing high risk of getting HIV. For example, if they have sex every week. This is because taking PrEP daily maintains protective levels of the drugs in the body. This means you do not need to plan taking PrEP around when you may have sex.

When taken daily, PrEP offers protection against HIV for both anal and vaginal sex. It can also be taken by MSM and heterosexual people, including trans men, trans women and non-trans (cis) men and women.

1. Daily dosing

This involves taking a single pill continuously, every day.

It should be taken at approximately the same time each day as part of your daily routine. Although occasionally taking it 2 hours early or late is ok.

2. Intermittent dosing (also known as ‘T’s and S’s’ or 'TTSS')

This involves taking a single pill regularly 4 times a week on a Tuesday, Thursday, Saturday and Sunday.

It is important to note that taking PrEP in this way allows NO leeway for missed doses so is only suitable if you are confident you will not miss any doses.

Regular dosing may be started by taking a double dose (2 pills) for the first dose before sex. This gives protection within two hours.

Event based dosing (sometimes called event driven (ED) or on-demand (OD) dosing.

This involves only using PrEP when you want to have sex. It may be appropriate for people who have sex less often than once a week and who usually know when they may be likely to have sex. It can’t be used it you have hepatitis B.

1. 2:1:1 dosing:

This 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 dose.

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 cannot be used for receptive vaginal/frontal sex.

2. 2:7 dosing:

This 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 dose.

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

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

Starting PrEP

How to start taking PrEP

To start oral PrEP, you should take double dose (two pills) BEFORE sex for the first dose. This gives you protection within two hours.

Stopping PrEP

How to stop taking PrEP

Regular dosing:

Before stopping daily or intermittent dosing, you need to continue for either 2 or 7 days after you last had sex. This depends on how long you are taking PrEP.

Event-based dosing:

Before stopping event-based dosing, you need to continue daily dosing for either another 2 days (2:1:1 dosing) or 7 days (2:7 dosing).

Missed doses

It is really important that you take PrEP as directed. Its effectiveness in reducing the risk of getting HIV is dependent on it being taken properly. If you are unable to do this and miss tablets regularly, PrEP may not work.

What to do if you miss a dose

Regular daily dosing

One of the benefits of taking PrEP daily is that occasionally missing a dose will not stop it from working. Everyone taking daily PrEP will get good protection so long as you take at least four pills every week:

If you are missing several doses each week, please speak to your clinic. We can try to support you with this.

If you use daily dosing and miss more than a week of pills, you will need to start again with a double (2-pill) dose to get full protection.

Regular 'TTSS' dosing and event-based dosing

If you are using 'TTSS' dosing or event-based dosing, it’s really important not to miss any doses.

If you are late with, or miss a dose, you should take the dose as soon as you remember. But, if it’s been 24 hours since the time you should have taken it, do not take the missed dose AND
If you think you might have been at risk of getting HIV when you weren’t taking PrEP, or didn’t take enough, please contact your clinic. We can discuss whether you need post-exposure prophylaxis (PEP) and another HIV test.

For more information on how to take PrEP, please visit:

UK Guide to PrEP

Other considerations

Things to consider before starting taking PrEP.

Side effects whilst taking PrEP

Most people who take PrEP don’t experience side effects. But, like all medicines, it can cause side effects in some people.

Often side effects are only experienced during the first few weeks of taking PrEP. This is because your body is getting used to taking it. These symptoms are usually minor and include:

tiredness
gastrointestinal issues such as feeling sick, bloating and diarrhoea
headaches

Whilst long term side effects are rare, occasionally, taking PrEP can affect the kidneys or bones:

These effects should stop after stopping taking PrEP. Your kidney function will be monitored whilst taking PrEP so any problems can be detected early.
If you have bone or kidney problems, or are high risk, you may be offered a different type of PrEP. This can provide protection against these side effects.

For more information about side effects, please read the patient information leaflets supplied with PrEP.

The ingredients of the medication may vary depending on the brand you are given. Always check the patient information leaflet supplied with your medicine to check that it does not contain any ingredients that you are allergic to. Speak to your clinician if you think you may be allergic to any of the ingredients.

Taking PrEP with other medications

PrEP does not interact with most other medicines but, tenofovir disoproxil, one of the medicines in the most commonly-used type of PrEP, should be used with caution with some other drugs that can affect the kidneys. This includes non-steroidal anti-inflammatory drugs (NSAIDs), for example, ibuprofen and naproxen. Taking both types of drugs together can increase the risk of kidney problems.

Tell your clinician if you are taking any other medicines so they can check that they are safe to take with PrEP. This includes:

herbal medicines
complementary medicines
medicines you buy over-the-counter
medicines you buy online
recreational drugs

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

PrEP, pregnancy and breastfeeding

Speak to your clinician if you could be, or are, pregnant or if you are breastfeeding:

If there is a risk that you could be pregnant, you will be asked to do a pregnancy test as a part of our initial assessment and monitoring processes. PrEP may be taken by those who are pregnant or breastfeeding if there is an ongoing risk of getting HIV but your clinician will discuss the potential risks and benefits of this with you.

Storing PrEP

What to do next

If you want to start taking PrEP, call your local iCaSH clinic on 0300 300 3030. They will take your details and put you on a waiting list. When it's your turn, the clinic will contact you to book a first appointment.

First appointments

This appointment will help decide if PrEP is right for you, and the best way for you to take it. This may be a teleconsultation.

At the appointment you will be asked some questions about:

your sexual behaviour and sexual partners
your medical and vaccination history
any medicines that you take.

Before starting PrEP, you will need to have an HIV test to check that you don’t have HIV. You will also be tested for other STIs, like hepatitis B and C. Your kidneys will be checked and, if appropriate, a pregnancy test will be taken.

You will also be offered vaccination against hepatitis A and B, human papilloma virus (HPV), syphilis and mpox, if appropriate.

Once your test results are back, a clinician will discuss these with you. If PrEP is right for you, they will arrange a supply of the medicine for you. Most patients will get a 3-month supply in the first instance, which you will need to collect from the clinic.

Whilst long term side effects are rare, occasionally, taking PrEP can affect the kidneys or bones:

These effects should stop after stopping taking PrEP. Your kidney function will be monitored whilst taking PrEP so any problems can be detected early.
If you have bone or kidney problems, or are high risk, you may be offered a different type of PrEP. This can provide protection against these side effects.

For more information about side effects, please read the patient information leaflets supplied with PrEP.

The ingredients of the medication may vary depending on the brand you are given. Always check the patient information leaflet supplied with your medicine to check that it does not contain any ingredients that you are allergic to. Speak to your clinician if you think you may be allergic to any of the ingredients.

Follow up appointments after starting PrEP

When you open your last month’s supply of PrEP, you will need to contact your clinic to book a follow-up appointment, if you don’t already have one booked. This appointment will probably be a telephone call.

If you wait until you’ve run out, or nearly run-out of PrEP before booking your next appointment or requesting your next supply online, we may not be able to supply you with further PrEP in time. This means you might have to stop taking PrEP for a while. If this happens, you could lose the protection that PrEP gives you, and you may need to start taking it again and wait for it to work.

You will need to be tested for STIs, including HIV. This may be done using a free self-testing kit.

It is also important to do the tests your clinician asks for. These need to be completed to enable us to continue to supply PrEP to you.

Your kidneys will be checked at least once a year whilst taking PrEP. They may be checked more frequently if you are at an increased risk of side effects affecting your kidneys.

A pregnancy test may be taken too, if appropriate.

At your follow up appointment, the clinician will check:

that PrEP is still suitable for you
for any side effects
that you have been taking it correctly

If continuing on PrEP, your new supply of medicine will be made available for you to collect.

After your second supply of medicine, you may be offered to request your next supply of PrEP and have a follow-up online via the iCaSH PrEP+ Service. Your clinician will discuss this with you if this is an option.

Online PrEP+ Repeat Supply Service

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