What is PrEP?

PrEP stands for Pre Exposure Prophylaxis.

It is a way for an HIV negative person to use HIV drugs to protect against catching HIV.

PrEP uses two HIV drugs (tenofovir DF and FTC) in one pill. For highest levels of protection PrEP needs to be taken before and after sex.

Most PrEP studies – including the UK PROUD study – involved taking one pill every day, even when not having sex. In studies where people were good at not missing doses, there was close to 100% protection.

Other ways of using PrEP have also been studied, which only use PrEP when someone thinks they are likely to have sex. This is called event based dosing (EBD).

One of these studies, called IPERGAY, used a double-dose 24 to 2 hours before sex, with two post-sex single doses 24 and 48 hours after the first dose.

EBD only provides protection for anal sex whereas daily dosing works for both anal and vaginal sex.

PrEP was approved in the US in 2012 and was quickly included as a key recommendation in World Health Organization (WHO) guidelines. PrEP was only approved in Europe in July 2016.

NHS England decided to block access in June 2016. However, many people in the UK buy generic PrEP online. This is just as effective as the brand name drug but much cheaper. It is legal and safe to buy onlne meds.

PrEP is currently available on the NHS in Scotland, Wales and Northern Ireland. It is only available free in England by joining the PrEP Impact Study.

For more information see:

What is PEP and PEPSE?

PEP stands for Post Exposure Prophylaxis.

This involves using a combination of three HIV drugs after sex if there has been a significant risk – and taking them for a month. The word PEPSE  is sometimes used – it stands for PEP after Sexual Exposure.

PEP needs to be taken as soon after exposure as possible. This is preferably within hours rather than days. Most guidelines have a cut off for PEP of 48 hours after exposure.

Even though in the UK you can get PEP for up to 72 hours it is much less likely to work when it is used this late.

The longer the delay the less the chance that PEP will work.

Before getting PEP you will need to talk about your risk. This involves talking about the type of sex and whether you know the HIV status of your partner.

You also need to have a rapid HIV test which gives the result within 30 minutes. This test only tells you whether you were HIV positive three months ago. It tells you nothing about the recent risk.

You need an HIV test because if you are HIV positive without knowing it, a short-course of treatment could cause drug resistance.

You can get PEP at any accident and emergency (A&E) department of a hospital 24 hours a day. You can also access PEP from a GUM clinic during working hours.

After a course of PEP you need to wait 28 days before testing for HIV. This is because PEP can delay infection.

Can I use my partner’s meds as PEP?

Using someone else’s meds is not recommended. Some HIV drugs should never be used as PEP.

However, two HIV drugs have been studied for preventing HIV. These are tenofovir and FTC (in one pill called Truvada). A single dose of Truvada would provide more rapid cover while you get to a clinic and wait to be seen.

Several studies have shown that daily Truvada reduces the chance of HIV transmission when taken by HIV negative people. These studies also showed Truvada to be safe.

This would only be recommended as a single dose while you are waiting to get to HIV clinic for PEP.

However, if the HIV positive person is already on treatment and has an undetectable viral load, they will also be much less infectious. In these circumstances some guidelines think the risk is so low as to not recommend PEP.

HIV meds that must NOT be used as PEP include:

  • Any type of NNRTI (nevirapine, efavirenz, etravirine or rilpivirine).
  • Atripla or Eviplera (which both contain an NNRTI)
  • Abacavir (or Kivexa or Trizivir that contain abacavir).

This is because these drugs have a low risk very serious side effects, including hypersensitivity reactions and severe skin rash. With some NNRTIs the risk can be higher for someone with a stronger immune system that when they are used for treatment in someone who is HIV positive.


What is TasP?

TasP stands for Treatment as Prevention. (See Viral Load).

It refers to the impact of HIV treatment – when taken by an HIV positive person – on reducing the risk of transmitting HIV.

This is because treatment reduces HIV to levels that are too low to be infectious.

This was known in 2001 for heterosexual couples. In 2008, a group of Swiss doctors said that they believed this risk to be zero in a paper called the Swiss Statement. The doctors were sufficiently sure that they said it was safe to have a baby this way, if the man was positive and on treatment and the women was HIV negative.

In 2012, another heterosexual study called HPTN-052 showed treatment reduced the risk of HIV by 96%.

Then in 2014, the PARTNER study reported no linked HIV transmission in over 900 couples and after more than 44,000 times when people had sex without a condom. PARTNER included both gay and straight couples and incuded anal and vaginal sex. See page 16 for more details.

In the UK, every HIV positive person can access HIV treatment if they want to be less infectious to partners.

New guide to PrEP in the UK (June 2016):

See also this link for more information.

Last updated: 1 June 2019.