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PrEP (Pre-Exposure Prophylaxis)

a bottle of pills

Pre-exposure prophylaxis (PrEP) is a course of HIV drugs taken before sex to reduce the risk of getting HIV. It could one day be widely available to those who are at high risk of coming into contact with the virus.

  1. What is PrEP?
  2. How does PrEP work?
  3. How often do you take it?
  4. Who could take PrEP?
  5. Where do I get PrEP?
  6. What about other sexually transmitted infections?
  7. How well does it work?
  8. Is PrEP safe?

What is PrEP?

PrEP is a course of HIV drugs taken by HIV negative people before sex to reduce the chance of getting HIV.

Results in trials have been very successful, with PrEP significantly lowering the risk of becoming HIV positive and without major side effects.

The medication used for PrEP is a tablet called Truvada, which contains tenofovir and emtricitabine (which are drugs commonly used to treat HIV).

How does PrEP work?

Taking HIV medication before being exposed to HIV means there is enough drug inside you to block HIV if it gets into your body - before it has the chance to infect you.

How often do you take it?

In clinical trials PrEP has been used in two different ways:

  • taken regularly (one tablet per day)
  • only taken when needed (two tablets two to 24 hours before sex, one tablet 24 hours after sex and a further tablet 48 hours after sex).

This is often called ‘on-demand’ or ‘event based’ dosing.

Both methods have been shown to be very effective, although on–demand dosing has only been studied in gay and bisexual men.

If PrEP becomes available in the UK it is likely that both approaches will be used, depending on what is most suitable.

Who could take PrEP?

People who are at high risk of getting HIV. This includes gay and bisexual men, black Africans, trans people and those in a relationship with an HIV positive partner who is not on successful treatment.

Where do I get PrEP?

At the moment PrEP is not available on the NHS but it’s available by private prescription from some sexual health clinics.

Some people are ordering a cheaper, generic version of Truvada (called Tenvir-EM) from online pharmacies.

If you’re thinking about getting PrEP from outside the NHS it’s important that you talk to an adviser from a sexual health clinic. Many will support you to use the treatment safely and provide necessary tests (eg, kidney function tests).

What about other sexually transmitted infections?

Research has shown that PrEP is highly effective at preventing HIV as long as it’s taken as directed.

However, PrEP will not protect you from other sexually transmitted infections (STIs) or an unwanted pregnancy - whereas condoms will.

If you’re using PrEP it’s important that you go for regular STI screens every three months so you can get any other infections treated.

How well does it work?

In most big PrEP studies, no one became infected if they took PrEP as recommended. But if you don’ not take it correctly it may not work.

The UK’s PROUD study reported an 86 per cent reduction in HIV infections in gay men taking PrEP - this figure included people who did become infected with HIV but were not taking PrEP at the time they were infected. The protection PrEP offers is thought to be near complete when taken as prescribed.

Is PrEP safe?

The drugs used in PrEP are the same drugs that are prescribed to thousands of people living with HIV every year. They are very safe and serious side effects are very rare. A few people experience nausea, headaches or tiredness and, very rarely, the medication can affect kidney function.

As a precaution people taking PrEP have regular kidney function tests.

More information:

If you like to speak to someone about PrEP, call THT Direct on 0808 802 1221.

‹‹ Back to: PEP - Post-exposure prophylaxis



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The Information Standard: Certified member

This article was last reviewed on 9/8/2016 by Kyle Christie

Date due for the next review: 9/8/2019

Content Author: Cary James

Current Owner: Kerri Virani

More information:

UK guideline or the use of post-exposure prophylaxis for HIV following sexual exposure (2011), P Benn MBChB FRCP*, M Fisher MBBS FRCP† and R Kulasegaram LRCP MRCS FRCP‡, on behalf of the BASHH§ PEPSE Guidelines Writing Group Clinical Effectiveness Group., British HIV Association (BHIVA)

Post-exposure prophylaxis (PEP), Michael Carter, Greta Hughson, September 2012, NAM aidsmap

Prevention in focus -- Can we prevent infection with exposure? The world of post-exposure prophylaxis (PEP), CATIE (Canadian AIDS Treatment Information Exchange) Harlon Davey, Laurel Challacombe and James Wilton, 2010

HIV/AIDS, Fact sheet No 360, World Health Organisation, November 2012 (Updated November 2015)

PrEP briefing paper, Roger Pebody, NAM aidsmap, July 2015

How soon should PEP be used? Gus Cairns, NAM aidsmap

Pragmatic Open-Label Randomised Trial of Pre-Exposure Prophylaxis: the PROUD study, PROUD, MRC Clinical Trials Unit & Public Health England, February 2015

HIV in the United Kingdom: 2014 Report, Public Health England, November 2014

PROUD study interim analysis finds pre-exposure prophylaxis (PrEP) is highly protective against HIV for gay men and other men who have sex with men in the UK, PROUD, MRC Clinical Trials Unit & Public Health England, October 2014

Second European PrEP study closes placebo arm early due to high effectiveness, Gus Cairns, NAM aidsmap, October 2014

Risk of Drug Resistance Among Persons Acquiring HIV Within a Randomized Clinical Trial of Single- or Dual-Agent Preexposure Prophylaxis, The Journal of Infectious Diseases, March 2014

Next steps for PrEP: Getting a proven prevention option to the people who need it, Deirdre Grant and Kay Marshall, Treatment Issues, June 2013

An Angle on Long-Term Side Effect Risk With TDF/FTC PrEP in Weighing Risks of TDF/FTC PrEP Side Effects in People Without HIV, Mark Mascolini from The Center for AIDS, The Body Pro, Winter 2012

Emtricitabine-tenofovir concentrations and pre-exposure prophylaxis efficacy in men who have sex with men, Anderson PL1, Glidden DV, Liu A, Buchbinder S, Lama JR, Guanira JV, McMahan V, Bushman LR, Casapía M, Montoya-Herrera O, Veloso VG, Mayer KH, Chariyalertsak S, Schechter M, Bekker LG, Kallás EG, Grant RM; iPrEx Study Team; Science Translational Medicine, September 2012

Antiretroviral Prophylaxis for HIV Prevention in Heterosexual Men and Women, The New England Journal of Medicine, August 2012

PrEP Works... If You Take It, PrEP efficacy table from www.prepwatch.org

PROUD study website

PreP briefing paper, Roger Pebody NAM, Aidsmap, July 2015

HIV in the UK: Situation Report 2015, Skingsley A, Yin Z, Kirwan P, Croxford S, Chau C, Conti S, Presanis A,  Nardone A, Were J,  Ogaz D, Furegato M, Hibbert M, Aghaizu A, Murphy G, Tosswill J, Hughes G, Anderson J, Gill ON, Delpech VC and contributors; Public Health England, November 2015

HIV and AIDS - prevention, NHS Choices, September 2014

Viral load, Michael Carter and Greta Hughson, NAM, Aidsmap, March 2014

PEP, PESE, PrEP and TASP!, iBase, February 2013

HIV in the UK: 2014 report, Zheng Yin, Alison Brown, Gwenda Hughes, Anthony Nardone, O.Noel Gill  and Valerie Delpech. The HIV and AIDS Reporting Team, HIV and STI Department, Centre for Infectious Disease Surveillance and Control, Health Protection Directorate, Public Health England, November 2014

PROUD PrEP study results published, Gus Cairns, NAM, Aidsmap, September 2015

PEP stopwatch

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The easiest and most effective precaution to take against most STIs is using a condom.