A Guide To: Pre-exposure prophylaxis (PrEP)

Last month, Pre-exposure prophylaxis or ‘PrEP’ – the drug that prevents HIV infection – finally became available on the NHS. We sat down with Kath Charters from Sahir House to learn more about the drug, how it works and how to access it.

What is PrEP?

Pre-exposure prophylaxis (PrEP) is a HIV prevention strategy that uses antiretroviral drugs to protect HIV negative people from HIV infection. People take PrEP when they are at risk of exposure to HIV, in order to lower their risk of infection.  PrEP is highly effective in preventing the sexual transmission of HIV, as long as the drugs are taken regularly, as directed. However, PrEP does not prevent other sexually transmitted infections or pregnancy.

How does PrEP work?

PrEP works in the following way. A person who does not have HIV takes enough antiretrovirals for there to be high levels of the drugs in their bloodstream, genital tract and rectum before any exposure to HIV. If exposure occurs, the ARVs stop the virus from entering cells and replicating. This prevents HIV from establishing itself and the person remains HIV negative. The antiretrovirals which are currently used as PrEP were chosen because they have limited side-effects, have few problems with drug resistance, reach high levels in the genital tract and rectum, and remain in the body for a relatively long time.

When was PrEP first used?

In 2012, the FDA approved the drug for use as pre-exposure prophylaxis (PrEP) based on growing evidence that the drug was safe and effective at preventing HIV in populations at increased risk of infection. The PrEP IMPACT Trial launched across England in October 2017 with a total of 10,000 places.

How effective is PrEP?

In a study done with gay men in England, use of Truvada as daily PrEP reduced HIV infections by 86%. In a study with gay men in France, PrEP taken before and after sex also reduced infections by 86%.

In studies, when PrEP appears not to have worked for someone, this was because the person was not actually taking the medication as directed. In people who are able to take PrEP regularly, only occasionally missing doses, PrEP appears to prevent almost 100% of infections.

You can find out more here: https://www.aidsmap.com/about-hiv/pre-exposure-prophylaxis-prep

How many people in the UK currently use PrEP?

The estimated number of people currently using PrEP is 17,500 – 18,500. It is important to note that not everyone goes through clinics or were on the PrEP trial, some people are buying their PrEP from the PrEPster website.

What are the risks and/or side effects?

Less than one in ten people report side effects such as feeling sick, flatulence, abdominal pain, dizziness and headache in the first month of PrEP use. These side effects are usually mild and short-lived. Typically, they start in the first few days or weeks of PrEP use and last a few days, and almost always finish within a month.

One of the drugs used in PrEP, tenofovir disoproxil fumarate, can put additional strain on the kidneys in people who already have kidney problems. A blood test to check kidney function is required around the time of starting PrEP and at least once a year while on PrEP, to monitor this.

A slight decrease in the hardness of bones has been seen in the first six months of taking PrEP. This reduction in bone density is small (0.5-1.5%) and will not make a difference to people with normal bone density prior to using PrEP. So far there have not been any reports of bone fractures related to PrEP use.

Who should consider PrEP?

People who have sex with a partner who is a person living with HIV (PLHIV), anyone who has condomless sex with a partner whose status is unknown, and those who share needles to inject.

Please note that U=U (undetectable = untransmittable).  U=U has been a game changer in the area of HIV prevention and HIV treatment and care. If you have HIV and are taking your medication as prescribed, it is fully expected you should be able to achieve what is known as an undetectable viral load. This means your body is controlling the virus and you have so little virus that is active in your bloodstream you cannot transmit it sexually to another person. This ordinarily can be achieved within months of starting on treatment and you would be carefully monitored to the point where your body has been able to maintain an undetectable viral load for three months before your treatment team advises you would not be able to transmit the virus to sexual partner/s.

If a person is having sex with someone who is living with HIV, they are monogamous and the person is on effective HIV medication and has an undetectable viral load, PrEP may not be needed and we would advise speaking to a specialist sexual health care practitioner to discuss any concerns and recommendations

Find out more here: https://www.aidsmap.com/about-hiv/what-does-undetectable-untransmittable-uu-mean

If PrEP prevents HIV, why aren’t more people using it?

The answer to this is something that perhaps can only be speculated. One reason might be effective medication that people living with HIV can take to reduce the virus and take them to levels where the virus is undetectable which has proven to reduce risk of transmission to zero. If their status is known to their partner/s they may decide there is no risk of onward HIV transmission and choose not to use PrEP.

PrEP has not been well promoted to cis-women who may be at risk of HIV transmission and whilst there have been campaigns to address this, the uptake is lower than anticipated certainly during the IMPACT Trials.

Dosing for PrEP is different for different types of sex. For example, on-demand dosing for people whose HIV risk is through vaginal sex is not recommended. Daily dosing is the only recommended regimen for vaginal sex. For people who are having infrequent vaginal sex other HIV prevention resources might be more appropriate, e.g. condoms.

People who have lived through the AIDS epidemic may choose to use condoms to prevent HIV transmission as this is a proven method, It can also be more spontaneous than thinking about dosing with PrEP and will prevent other STI transmissions.

PrEP has not been well promoted to people in BAME communities and campaigns have been launched alongside the rollout of PrEP to address this inequity in access to information and services. You can read more about this on the Terrence Higgins Trust website.

Why has it only recently become available on the NHS?

PrEP is now available free on the NHS in England and Wales from sexual health clinics. PrEP, as with other drugs, needed to be trailed to prove its efficacy. Once proven, and proven to be a game changer for HIV transmission rates, its efficacy was not in doubt and should now be made available to all who may be at risk of HIV transmission.

Is PrEP available privately?

Yes, PrEP is available online and has been throughout the IMPACT trial period at PrEPster. You can find these sites below.



So is PrEP now easily and freely accessible via the NHS?

In theory yes, but roll-outs can take time. Following the announcement of the PrEP grant determination for 2020-21, councils in England can finally provide uncapped access to the HIV prevention drug. Speaking after the announcement, Richard Angell, Head of Policy and Public Affairs at Terrence Higgins Trust, said: “The Health Department has finally allocated funds to local government to start the rollout [of PrEP]. There should now be nothing standing in the way of this important HIV transmission prevention drug finally becoming a reality in England. This follows years of painstaking battling and further delays due to COVID-19.

“We now need to see PrEP made rapidly available right across the country – the wait has been too long. We know hard-working local officials and many clinics put the wheels in motion for a start of October launch to make the most of this game-changer for HIV prevention – this allocation of funds should mean people are ready to go. More work is needed to ensure all groups affected by HIV know about PrEP and how to access it, but this is undoubtedly an important step forward as we work towards ending HIV transmissions in England by 2030.”

Read more about this here: https://www.tht.org.uk/news/wait-finally-over-hiv-prevention-pill-prep-england

What are the most important facts everyone should know about PrEP?

Before starting PrEP it’s important to know for sure that you don’t have HIV. Make sure you use a ‘4th generation’ HIV test – these tests are better at picking up recent HIV infection than older generation tests. ‘4th generation’ HIV tests are usually only available in sexual health clinics: finger-prick HIV tests, including those available to test yourself, are not as good at picking up recent HIV infection.

If you’ve experienced recent flu-like symptoms, after an HIV risk, then it is important not to start PrEP. The symptoms could be of recent HIV infection and you should seek support and advice from a sexual health clinic.

Visit a sexual health clinic to discuss PrEP and other STI prevention information, at clinic you will be given advice and information on the best protection methods for you with the type of sex yourself and your partner/s have taking into account your medical history, if there is a need for contraception and so forth.

For help and advice regarding PrEP, you can go to your local sexual health clinic – https://www.axess.clinic/

PrEP Recommended Reading






Over the past three decades award winning charity Sahir House have been providing care, support and practical assistance to people living with HIV, their partners, carers, dependants and improving public education in connection with the effects of HIV in the Merseyside area. You can learn more about the organisation at www.sahir.org.uk

Image credit: NIAID https://www.flickr.com/people/54591706@N02


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