What is HIV PrEP?

HIV PrEP is a medicine that stops you getting HIV. HIV is a virus that affects your immune system if left untreated. The most common way to get HIV in the UK is through unprotected anal, vaginal or frontal* sex.

PrEP stands for Pre-Exposure Prophylaxis. “Pre-exposure” means it is taken before sex and “Prophylaxis” means to prevent disease – in this case by stopping you getting HIV. If taken correctly, it is highly effective at stopping HIV being passed on.

HIV PrEP tablets contain two drugs called Tenofovir and Emtricitabine in a single tablet. These drugs have been used in HIV care for many years.


*frontal sex is an alternative term for vaginal sex used by some trans and non-binary people.

HIV PrEP is not a treatment for people living with HIV. The HIV PrEP tablet cannot treat HIV on its own and should not be used for this.

If your partner is living with HIV, has been taking HIV treatment for at least 6 months and has an undetectable HIV viral load, you are not at risk of HIV transmission through sex. People living with HIV who are taking effective HIV medication will usually have an undetectable level of HIV in their body. Someone who has an undetectable HIV viral load cannot transmit HIV through sexual practice. This is sometimes called undetectable equals untransmittable, or U=U.

At your first HIV PrEP consultation the doctor or nurse will ask you about your medical and sexual history. You will have tests that will check for HIV and STIs such as hepatitis, syphilis, gonorrhoea and chlamydia. If not already done, they will also check your kidney function.

It is important we make sure you do not have HIV before starting HIV PrEP. If you have had anal, vaginal or frontal sex with a man without using a condom in the 6-7 weeks before you start HIV PrEP, we will ask you to return to the clinic to have your HIV test repeated. This repeat test will be scheduled to take place four weeks after starting HIV PrEP. This is to make sure an early HIV infection is not missed. It is important to return for this appointment because you can develop resistance to HIV medications if you start HIV PrEP when you already have undiagnosed HIV.

There are two ways you can take HIV PrEP, called daily dosing and event based dosing. Event based dosing is sometimes called on-demand dosing. You can change between daily and event based dosing but speak to your sexual health service first. They will support you to make changes safely.


Daily dosing means you take one tablet every day. Taking HIV PrEP every day ensures protective levels of HIV PrEP in your body 24 hours a day, 7 days a week. If you’re more likely to have unplanned sex or cannot predict when sex is likely to occur, daily dosing provides the best protection.  You will be protected once you have taken seven HIV PrEP pills in a row.

Event based

Event based dosing works when you know when you’ll be having sex and can plan in advance. Event based dosing should only be used if your only risk of getting HIV is from anal sex.  Event based dosing is when you take HIV PrEP pills before and after each episode of sexual activity. This means you:

  1. Take two tablets of HIV PrEP before you have sex. Ideally this should be between 2 and 24 hours before sex.
  2. Take one tablet of HIV PrEP every 24 hours until you have had two sex free days.

Event based dosing is not an option if you have hepatitis B.

Event based dosing



How you take HIV PrEP depends on what type of sex you have and your own personal preferences. The doctor or nurse at the sexual health clinic will discuss what’s important to you, make sure you feel confident with your chosen option and you know how to take HIV PrEP. It’s easy to forget to take a tablet; missing a dose of your HIV PrEP may put you at risk of getting HIV, so it is important to take PrEP as you have been advised. Setting mobile phone reminders can be a simple way to help you keep track of when you take your HIV PrEP.

Most people who take HIV PrEP do not get any side effects.

Around 1 in 10 people will experience mild nausea, diarrhoea, headache and bloating but these symptoms usually go away after about a month.

Sometimes HIV PrEP can affect your kidneys and bones. This is why sexual health services will perform kidney tests before and during treatment and ask about your medical details.

It is safe to take most other medicines at the same time as HIV PrEP. However, if you are starting any new medicines, always tell the doctor or nurse you are taking HIV PrEP so that they can check if they are safe to use together. If you are using HIV PrEP don’t take ibuprofen, diclofenac or naproxen, or any other medicines from a group of painkillers called non-steroidal anti-inflammatory drugs or NSAIDs.

HIV PrEP can safely be used with all methods of contraception.

HIV PrEP is safe for transgender or non-binary people who are taking hormones.

You and the doctor or nurse should come to an agreement whether HIV PrEP or another option is the right HIV prevention option for you.

You can usually start HIV PrEP at your first clinic appointment. You are usually asked to go back after one month to make sure you are okay with the tablets.

Every three to six months you will need a blood test for HIV and syphilis, a urine test to check your kidney function and swab tests for other STIs.

Every twelve months you will need a blood test to check your kidney function.  If you are taking some other medications, or if you have high blood pressure, you might need to have a blood test for your kidney function more regularly than this.

HIV PrEP is not available from NHS Scotland outside of sexual health services and you cannot get an HIV PrEP prescription from your GP.

You can decide to take a break from HIV PrEP or to stop using it altogether. You can discuss stopping or taking a break from HIV PrEP with a member of staff, so that you are confident about how to do this safely. How you stop HIV PrEP depends on the sort of sex you last had and the doctor or nurse will give you advice about this.

If you have a break from HIV PrEP and have any risks during this time, it is important to have another HIV test.

A medication called Post Exposure Prophylaxis or PEP can be accessed from any sexual health service or from Accident and Emergency services out of hours. You need to take it within 72 hours and ideally within 24 hours – of the risk event. PEP is effective at preventing HIV transmission following a sexual risk.

Download the what do I need to know about HIV PrEP booklet

A downloadable booklet (PDF) for people who have discussed HIV PrEP with a healthcare professional and have been prescribed PrEP. It explains how PrEP works, the different ways PrEP can be taken, how PrEP supports sexual health, what happens at appointments and how your health will be monitored while using PrEP.