Everything your need to know about PrEP

We answer the common questions about the game changing HIV drug

PrEP or Pre Exposure Prophylaxis is a drug which reduces the risk of contracting HIV by 90% or more. Following success in the US, a limited trial has been released in England and the drug is due to be fully accessible by 2020. We answer a number of questions surrounding the drug that could change the face of sexual health and end new HIV transmissions in the not too distant future.


What is PrEP or pre-exposure prophylaxis?

PrEP stands for pre-exposure prophylaxis and it refers to the use of HIV drugs as a way to prevent HIV negative people from contracting HIV. Broken down, it means: –

  • “Pre” – Taken before
  • “Exposure” – Exposure to HIV through sex or injected drugs
  • “Prophylaxis” – This refers to a treatment to prevent disease

It is usually administered in tablet form and made up of Tenofovir and Emtricitabine. These are the two most common drugs that are used in the effective management of HIV. Sometimes PrEP may be referred to by its brand name, Truvada, but most PrEP used in the UK is in a generic form.

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How does PrEP work?

PrEP works in a similar way to how anti-malarial medication works when you go to a tropical country. It’s a mixture of the two most common antiretroviral drugs that are used to fight the virus in HIV positive individuals. When taken regularly before sex by a HIV negative person, enough of the medication remains in the body to fight the virus after you are initially infected.

Basically, PrEP acts as a shield. To be more specific, if you take PrEP regularly then it remains in your bloodstream, genital tract and rectum in an amount that can fight the first contact with the virus. Rather than being able to multiply in your body and take hold, the drugs kill the virus at source.

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How often should PrEP be taken?

As always, it’s important to listen to your doctor or chemist when taking any medication and advice offered may differ for each individual case. However, generally speaking there are two main ways of taking PrEP that are being trialled in the UK.

  • Taking one tablet per day two hours before you are likely to have sex
  • Taking PrEP “on demand” by taking two tablets two to 24 hours before sex, taking one tablet 24 hours after and then taking a further tablet 48 hours after sex.

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How effective is PrEP?

There have been a wide range of studies conducted across the world into the effectiveness of PrEP and results of these vary based on a variety of different conditions being used. If taken correctly, PrEP can reduce the risk of catching HIV by 90% or more. Some studies conducted in the US have suggested that the figure for efficacy is actually closer to 99%, whilst a UK trial conducted amongst men who have sex with men found the drug to lower risk by 86%.

This risk can obviously be reduced further still by using condoms during sex.

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What happens if you miss a dose of PrEP?

Missing a dose of PrEP has a negative effect on efficacy. According to the US website Prep Facts which gained its information from a US study, missing doses can have the following impact: –

  • 7 PrEP pills per week – 99% effective
  • 4 PrEP pills per week – 96% effective
  • 2 PrEP pills per week – 76% effective

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How long does it take for PrEP to work?

Studies carried out on gay men suggest that effective PrEP levels in the blood and rectum are reached a week following the beginning of treatment. For women, it takes around three weeks. This is because it takes longer for drug levels to build up to an effective preventative level in the vagina and cervix.

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Who should take PrEP?

PrEP is currently not fully accessible on the NHS and in areas where it is accessible different criteria are currently being trialled for access. In general, PrEP is intended for HIV-negative individuals who are at high risk of contracting HIV. High risk includes: –

  • People with HIV-positive partners
  • People who aren’t in an a sexually exclusive relationship and are either,
  • Men who have sex with men who have recently contracted an STD or who have had anal sex without using a condom in the last six months
  • Heterosexual men or women who regularly have sex with partners of unknown HIV status who belong to a high risk sub group. For example an individual with a partner who injects drugs or a woman who has bisexual male partners.
  • Sex workers who have unprotected sexual intercourse with partners

If you intend on purchasing the drug through private healthcare means or online chemists, it’s important that you choose a site with MHRA certification to ensure it’s legitimate. It’s also worth having the drugs independently tested before use if you are still unsure.

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Are there any negative effects of PrEP?

As with any drug, PrEP can have a small number of unintended side effects for various individuals, including: –

  • nausea
  • dizziness
  • headaches
  • fatigue
  • stomach cramps

These will usually only be apparent in the first few weeks of taking the drug until your body becomes accustomed to it. If these last longer than a few weeks it’s recommended you consult your doctor.

There are also a number of longer term effects for some people, including: –

  • Liver health – consult your doctor if you notice yellowing of the skin or jaundice
  • Kidney health – this will usually be assessed before taking the medication
  • Bone density – PrEP can affect your bone density over time making you more likely to experience fractures.

Long term effects only occur amongst people taking the drug for long periods of time and only in a small proportion of people.

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When will PrEP be available in the UK?

Currently only 13,000 people at high risk of HIV in England have access to PrEP, but this number is slowly increasing with the availability expected to double by 2020. This initial limited release, which is mostly limited to men who have sex with men, was to allow NHS England to assess its effectiveness before making the drug fully accessible to heterosexual men and women.

Luckily, PrEP is now fully available through the NHS in Scotland, Wales and Northern Ireland.

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Should you still take STD tests whilst using PrEP?

No matter what risk group you belong to, if you are a sexually active individual taking PrEP you are still at risk of STDs. Studies have shown that the drug is not 100% effective against HIV, whilst it’s completely ineffective against other common STDs.

STD tests are an effective way of preventing the spread of STDs because they allow you to diagnose and treat the condition before passing it on to another individual. If you’ve had unprotected sex with someone for the first time or you’ve slept with more than one person in the last year, you should get tested.

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What are the existing alternatives to PrEP?

There’s no doubt about the fact that PrEP is an effective way of preventing HIV, particularly if you’re within a group that is high risk. However, if PrEP is not accessible for you at this current time, it’s worth noting that there are still other ways to reduce the risk of catch HIV.

  • Condom Use – when used correctly condoms are still highly effective at preventing the spread of the virus.
  • PEP (post-exposure prophylaxis) – Although PEP is not as effective as PrEP, it can still be an effective last resort. It involves taking HIV medication after you have been in a risky sexual situation.
  • Effective medication – if you are sleeping with someone who has HIV, it’s important to ensure they are receiving treatment for the virus that reduces their viral load to an undetectable level.
  • Regular testing – although this won’t protect you, regular testing will stop the spread of the disease detecting infection early and receiving treatment

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