Dr Simran Deo

Medically reviewed by

Dr Simran Deo

Last reviewed: 06 Dec 2019

PrEP is a pill you can take to protect you from HIV.


What is PrEP & how does it work?

PrEP (pre-exposure prophylaxis) is an anti-retroviral medication that if taken before coming into contact with HIV, reduces the risk of contractingHIV. PrEP is highly effective in protecting against HIV infection if used by HIV negative people in at risk groups.

Studies have shown that the PrEP once- daily regime reduces the risk of getting HIV from sex by more than 90% with the risk being reduced further when this is combined with condom-use.

What does pre-exposure prophylaxis mean?

‘Pre-exposure’ means ‘before coming into contact with’ something, in this case the infection HIV. ‘Prophylaxis’ is a treatment that protects you from getting an infection.

Is PrEP right for you?

PrEP is for HIV negative people at high risk of acquiring HIV.

HIV can be transmitted through:

  • Unprotected sexual contact
  • Injecting drugs
  • Pregnancy, childbirth & breast feeding
  • Occupational exposure
  • Blood transfusion/ organ transplant

High risk people are considered to be:

  • HIV-negative MSM and trans women who report condomless anal sex in the previous 6 months and on-going condomless anal sex.
  • HIV-negative individuals having condomless sex with partners who are HIV positive, unless the partner has been on ART for at least 6 months and their plasma viral load is <200 copies/mL.
  • More vigorous sexual contact for prolonged periods of time
  • Having unprotected sex with persons of unknown HIV status
  • Having unprotected sex when unknowingly recently infected or persons undergoing seroconversion
  • Chem- sex/ injecting drug use chem-sex (slamming)
  • Group sex
  • Multiple sexual partners
  • Condomless sex with partners from a population group or country with high HIV prevalence

The CDC has created a helpful tool where you can calculate risk:

What tests do I need to have before I can take PrEP?

  • An HIV test within the last 4 weeks
  • A blood test for your kidney function within the last 4 weeks which includes serum creatinine and eGFR
  • Full STI screening including Hep B and C within the last 4 weeks
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Why is it important to be HIV negative before and during PrEP therapy?

This is because you could develop resistance to HIV medication if you were HIV positive and taking PrEP.

There have been cases of people who have unknowingly been HIV positive and started, or continued on, PrEP and then later developed resistance to the medication. This has then impacted on the treatments they could receive for HIV, and made it difficult to keep them healthy.

Aside from the impact it has on the care of that individual, it means that drug-resistant strains of HIV could then unknowingly be passed on to others as well.

Why is it important to know my kidney function before and during PrEP therapy?

The drugs contained in PrEP are processed by the body and excreted in the urine by the kidneys. If your kidney function is below normal levels of the medication can build up in the body to unsafe levels. This in turn can further damage the kidneys.

Kidney damage is a rare side effect of PrEP, especially in people who have normal kidney function, having occurred in only 1 in 1000 to 1 in 10,000 people.

As a result guidelines advise it is important to check your kidney function just before starting PrEP, and then every 12 months. In people over 40, or those with higher risk of kidney disease such as people who suffer from high blood pressure or diabetes, kidney function should be tested every 6 months while on PrEP.

How long after having unprotected sex should I test for HIV?

Fourth generation lab tests for HIV are over 99% accurate at detecting HIV from 4 weeks after an episode of unprotected sex.

It is still recommended that the test is repeated every 3 months after this even whilst on PrEP as no treatment is 100% effective.

Does PrEP work and is it safe?

Time to protection is about 2-3 days for anal sex and up to 7 days for vaginal sex. After 7 days, PrEP reaches maximum effectiveness against HIV during sex.

Studies have shown that the PrEP once-daily regime reduces the risk of getting HIV from sex by more than 90% with the risk being reduced further when this is combined with condom-use.

Where to get PrEP?

It is possible to get PrEP on the NHS, but whether you’re eligible depends on your risk and where you live. You can also get PrEP online. You should always be careful when buying treatment online and make sure a Doctor has reviewed your circumstances.

Buy PrEP online

At ZAVA, we offer a complete PrEP therapy service which works in the following way:

  1. Fill out our online questionnaire. This will ask you for all of the information our doctors need to decide if they can prescribe you PrEP
  2. If you’ve not already had an HIV, kidney function, and hepatitis B and C tests, you need to do this first. You can order test kits from us if needed, so you can test at home
  3. We can also send you an STI test kit which you can also do at home
  4. Once you have completed the online questionnaire, our doctors will be in touch once you’ve started taking PrEP to give you any advice or extra information you might need
  5. We will offer regular reminders about keeping your tests and medication up to date

You can contact our doctors for free at any time during your treatment if you need any help or support.

Get PrEP on the NHS

Certain people can get PrEP free on the NHS. Each country in the UK has different availability.

In England, the NHS is offering the medication as part of a clinical study called the Impact Trial. You can find out more about joining the trial here or by contacting any of the sexual health clinics closest to you.

If you live in Scotland, Wales, or Northern Ireland there are no limits on the amount of people that can access PrEP, but it is only available at particular clinics and there is an eligibility criteria you must meet before you it will be prescribed to you.

The NHS offers HIV testing free of charge to anyone, and a lot of clinics can give you same-day results. Home test kits are also available on the NHS for free.

You can get HIV testing for free at any of the places below:

  • sexual health clinics
  • some GP surgeries
  • some contraception and young people's clinics
  • local drug dependency services
  • an antenatal clinic, if you're pregnant

Other ways to get PrEP

Other ways you can get PrEP include:

How do I take PrEP?

When using a daily regimen of one pill a day of PrEP it is recommended that men take PrEP for 7 days and women for 20 days before being protected.

It is also recommended that PrEP is continued for 28 days following the last sexual exposure if PrEP is stopped at a later date.

There are different regimes for taking PrEP:

Daily dosing

  • This is when one tablet is taken daily
  • It should be taken at the same time each day but a few hours later or earlier is acceptable
  • It can be taken with or without food

On demand (or event-based) dosing.

  • Only for anal sex NOT vaginal sex
  • As effective as daily dosing
  • For expected condomless sex 24 hours in advance
  • Take two tablets 2-24 hours before the expected sexual episode
  • Take one tablet 24 hours after
  • Take one tablet 48 hours after the last episode of condomless sex
  • No tablets should be missed

4 Pills per week dosing or Ts and Ss dosing

  • If you have sex once or twice per month only
  • Maintains a good level of PrEP in the blood
  • Is taken on Tuesday/ Thursday/ Saturday and Sunday

Holiday dosing

  • This is based on a 7-day period where your risk of HIV exposure will be higher.
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What are the side effects of PrEP?

When used correctly, PrEP (emtricitabine and tenofovir) generally causes little or no side-effects. However, any medication has the potential to cause side effects which can vary from person to person.

As with most medication, vomiting, breathing difficulties, swelling of the skin or a rash may occur if you have an allergy or intolerance to any of the components of the medication. If you develop any of these symptoms after taking PrEP, stop it immediately and seek medical attention urgently.

Most people who take PrEP will not experience side effects, but if they do, these usually resolve within a few weeks. Common side effects include:

  • Diarrhoea or vomiting
  • Heartburn or indigestion
  • Headaches
  • Dizziness
  • Tiredness or insomnia
  • Abnormal dreams
  • Rashes
  • Pain or feeling weak
  • Changes in your liver enzymes
  • Changes in the levels of your blood sugar and blood fats
  • Lowering of your white blood cells

In the PROUD study participants reported few side effects, and almost everyone who stopped PrEP because of side effects were able to start PrEP again. No significant health effects have been seen in people who are HIV-negative and have taken PrEP for up to 5 years.

If you develop any of the above side effects or any other symptoms, please see your GP to investigate this.

Always make sure you read the patient information leaflet that comes with your medication before starting the medication.

How else can I avoid catching HIV?

Using condoms

Needle exchange programmes

HIV prevention implant

Medically reviewed by:
Dr Simran Deo Doctor

Dr Simran Deo qualified from St George’s, University of London in medicine in 2006 with a distinction in her written finals. She went on to specialise in general practice, obtaining the MRCGP certification in 2012. In 2014 she received a merit for the Diploma in Dermatology from Cardiff University.

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Last reviewed: 06 Dec 2019

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