What is HIV PrEP?

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

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

HIV PrEP tablets contain 2 drugs called Tenofovir and Emtricitabine in a single tablet. These drugs have been used in HIV care for many years.

You can get HIV PrEP for free from NHS Scotland sexual health services.

Download the HIV PrEP information leaflet (PDF, 328 KB)

Who should not take PrEP?

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're 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 pass on HIV through sex. This is sometimes called undetectable equals untransmittable, or U=U.

What will happen at my first appointment?

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

It's important to make sure you do not have HIV before starting HIV PrEP. If you've had sex with a man without a condom in the 6 to 7 weeks before you start HIV PrEP, you'll be asked you to return to the clinic to have your HIV test repeated. This repeat test will be scheduled to take place 4 weeks after starting HIV PrEP. This is to make sure an early HIV infection is not missed. It's important to return for this appointment as you can develop resistance to HIV medications if you start HIV PrEP when you already have HIV.

How do you take PrEP?

There are 2 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'll support you to make changes safely.


Daily dosing means you take 1 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'll be protected once you've taken 7 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 2 tablets of HIV PrEP before you have sex. Ideally this should be between 2 and 24 hours before sex.
  2. Take 1 tablet of HIV PrEP every 24 hours until you've had 2 sex free days.

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

Download the event based dosing diagram (PDF, 250 KB)

Choosing the right dosing for you

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
  • make sure you know how to take HIV PrEP

Missing a dose of your HIV PrEP may put you at risk of getting HIV, so it's important to take PrEP as advised. Setting mobile phone reminders can be a simple way to help you keep track of when you take your HIV PrEP.

Are there any side effects?

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

Around 1 in 10 people will experience mild nausea (feeling sick), diarrhoea, headache and bloating. 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 history.

What if I'm taking other medicines?

It's safe to take most other medicines at the same time as HIV PrEP.

If you are starting any new medicines, always tell the doctor or nurse you're taking HIV PrEP. They can check if they're safe to use together.

If you are using HIV PrEP do not take non-steroidal anti-inflammatory drugs (NSAIDs) such as:

  • ibuprofen
  • diclofenac
  • naproxen

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

Can you take PrEP with contraception?

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

What if I'm pregnant or breastfeeding?

PrEP does not affect your ability to get pregnant.

PrEP can be safely used by women who are pregnant or breastfeeding.

When can I start taking PrEP?

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're usually asked to go back after 1 month to make sure you're okay with the tablets.

How will my health be monitored while I’m taking PrEP?

Every 3 to 6 months you'll need a blood test for HIV and syphilis, a urine test to check your kidney function and swab tests for other STIs.

Every 12 months you'll need a blood test to check your kidney function. You might need to have a blood test for your kidney function more regularly if you either:

  • take some other medications
  • have high blood pressure
Can I stop taking PrEP?

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 your doctor or nurse, so that you're 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've a break from HIV PrEP and have any risks during this time, it's important to have another HIV test.

You can get a medication called Post Exposure Prophylaxis (PEP) from any sexual health service or from A&E out of hours. You need to take it within 72 hours (ideally within 24 hours) of the risk event. PEP is effective at preventing HIV transmission following a sexual risk.

Last updated:
07 July 2022

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