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What is pre-exposure prophylaxis (PrEP)?

Truvada - the drug used as PrEP


  • Pre-exposure prophylaxis (PrEP) is a course of HIV drugs taken by HIV-negative people to prevent infection.
  • PrEP can virtually eliminate the risk of getting HIV if taken consistently and correctly.
  • PrEP won’t protect you against other sexually transmitted infections (STIs) such as hepatitis C. Condoms are still the best protection from these STIs.
  • PrEP is not taken for life – it is only taken for short periods when a person may be at risk of HIV infection.  

What is PrEP?

Pre-exposure prophylaxis (PrEP) is a course of HIV drugs taken by HIV-negative people to reduce their risk of HIV infection.

Truvada is currently the only drug approved for use as PrEP. Truvada is a single pill that is a combination of two anti-HIV drugs, tenofovir and emtricitabine.

How does PrEP prevent HIV?

The anti-HIV drugs in PrEP stop the virus replicating in your body. If you are exposed to HIV but have been taking PrEP correctly, there will be high enough levels of the drugs to prevent you from getting HIV.

How effective is PrEP?

If used consistently and correctly, PrEP can virtually eliminate the risk of you becoming infected with HIV.

A number of large, high profile trials undertaken across the world have continued to prove PrEP’s effectiveness.

If I take PrEP, can I stop using condoms?

This will depend on your circumstances. PrEP will protect you from HIV, but it doesn’t give you any protection against sexually transmitted infections (STIs). Using a condom is the best way to prevent other STIs such as gonorrhoea, chlamydia and hepatitis C.

Who can take PrEP?

PrEP isn’t recommended for everyone. It’s for people who are HIV-negative and more at risk of HIV infection.

PrEP may be an option for you if:

  • you’re in an ongoing sexual relationship with a partner living with HIV whose HIV is not well controlled.
  • you’re a gay or bisexual man who has multiple casual sexual encounters, and you don't always use condoms.
  • you’re a gay or bisexual man in a new sexual relationship but not yet aware of your sexual partners HIV status and not using condoms.
  • you’re not using condoms with partners of the opposite sex whose HIV status is unknown and who are at high risk of HIV infection (for example, they inject drugs, have multiple partners at the same time, or have bisexual male partners)
  • you’ve shared injecting equipment or have been in a treatment programme for injecting drug use.

Is PrEP effective for vaginal and anal sex?

PrEP can prevent HIV infection during both vaginal and anal sex, but the drugs in PrEP are absorbed much more effectively by rectal tissue than vaginal tissue. This means the options for how you take PrEP are different depending on the sex you have:

  • to prevent HIV infection through the vagina, PrEP needs to be taken every day. You will need to take PrEP for 7 days before you are protected, and then every day for as long as you want protection.
  • if your risk is from anal sex (being the receptive partner, or bottom) then you can consider daily PrEP (as above) or event-based (on-demand) PrEP. There are different types of event-based PrEP depending on your pattern of sexual activity, so make sure you talk this option through with a health professional.

Events-based or on-demand PrEP is only suitable for anal sex. Daily PrEP is the only method suitable for both anal and vaginal sex.

Where is PrEP available?

Currently, PrEP is not available everywhere in the world and even in countries where it has regulatory approval (meaning it’s approved as medication) it may not be easy to get hold of for a number of political or resourcing reasons.

In some countries PrEP is available for free, or subsidised as part of the national health system, in other countries you will have to pay for it privately.

The good news is that international guidelines now recommend that PrEP should be made widely available, so even if it's not available to you right now, it may be an option in the future.

If you are interested in getting PrEP contact a healthcare professional who should be able to advise you on how you can do this. They will also be able to offer the advice, monitoring and support to help you take PrEP correctly and ensure you are fully protected.

There are also dedicated websites that can help you buy PrEP. However, taking PrEP without medical advice and monitoring has health risks, so you should always get a professional health check if you do buy PrEP online.

How can I start PrEP and how long do I take it for?

You must take an HIV test before starting PrEP to be sure that you don’t already have HIV. If you have HIV already then starting and stopping PrEP may increase the likelihood of developing drug resistance.

While you’re taking PrEP, you should visit your healthcare professional for regular check-ups (at least every three months).

Unlike HIV treatment, people do not stay on PrEP for life. PrEP is normally taken for periods of weeks, months or a few years when a person feels most at risk of HIV. This might be during specific relationships, after the break-up of a relationship and dating new people, when planning a holiday when you know you will be sexually active with new people whose status you may not know, while dealing with drug use problems, or when trying to conceive and one of you is known to be HIV positive.

Does PrEP have any side effects?

In some people PrEP can cause minor side effects like nausea, vomiting, fatigue and dizziness, but these usually disappear over time.

In rare cases PrEP can also affect kidney functions.

If you’re taking PrEP and experience any side effects that are severe or don’t go away, tell your healthcare professional.

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Last full review: 
12 July 2017
Next full review: 
12 July 2020
Last updated:
22 October 2018
Last full review:
12 July 2017
Next full review:
12 July 2020