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HIV PrEP (Pre-Exposure Prophylaxis)

Pre-Exposure Prophylaxis (PrEP) is a course of medicine for HIV negative people to reduce the risk of catching HIV. It is a combination of 2 drugs in the form of a single table. This should be taken before sexual intercourse with another person who may have undiagnosed or untreated HIV infection.

PrEP has been shown to reduce the risk of HIV infection by up to 92% in those who take it properly. However, PrEP does not protect against other STIs and therefore, should be used in combination with other preventive interventions.

Method of treatment

Oral antibiotics


1 tablet/daily (can also be taken ‘on demand’ – see below)


Further actions

+ HIV & STI test every 3 months
+ Kidney function test every 12 months

Cost of treatment

£80/month (does not include consultation fee or baseline HIV test)


Same day appointments

In Birmingham Clinic


Highly confidential service

And discreetly located clinics


Specialists in sexual health

From busy NHS clinics

Do I need PrEP?

PrEP is an option for anyone who may be at a high risk of getting HIV infection. They may include individuals who are:

  • At a high risk of acquiring HIV infection when condoms are not used consistently.
  • HIV-negative men and have sex with men and do not use condoms consistently.
  • Transgender individuals who do not use condoms consistently.
  • Partners with someone who is HIV-positive and their partner is not taking HIV medications.
  • Partners with someone who is HIV-positive and their partner is taking medications but the virus is not fully suppressed.
  • HIV-negative heterosexual men and women with multiple sexual partners – some of whom are likely to have HIV infection and not be on treatment – and aren’t consistent with condom use.
  • Working in the adult industry, after individual assessment of their risks.

What tests do I need before starting PrEP?

The following tests are recommended before starting PrEP:

  • HIV blood test
  • Hepatitis B blood test (or evidence that you are immune against Hepatitis B)
  • STI and Hepatitis C screen (or evidence of negative test results since last exposure)
  • Blood test to rule out any abnormality in the kidney function
  • Urine test to rule out any abnormality in the kidneys
  • Pregnancy test (if required)

Why do I need to have these tests before starting PrEP?

The key reasons are:

  1. It will be inappropriate to start PrEP if one has already got the HIV infection.
  2. PrEP tablets have an antiviral effect on the Hepatitis B infection. Using these tablets in someone with undiagnosed Hepatitis B can be dangerous, especially when they are coming off PrEP.
  3. These medications can cause changes in kidneys, and therefore baseline readings help in monitoring.
  4. An STI and Hepatitis C screen can prevent transmission to their partners.

How often should I take PrEP?

There are two methods of taking PrEP (each can be discussed with your doctor):

Option 1: Daily (1 pill per day)

The best way to take PrEP is to take 1 pill every day at a fixed time to suit your lifestyle – this is so it becomes a part of your routine, but a few hours later or earlier is also fine. It can be taken with or without food (see above).

Option 2: Rule of 7

  1. Take 1 tablet daily for 7 days for the effect of PrEP to set in
  2. Keep taking tablets for 7 days after last exposure for maximum protection

Things to keep in mind with this method:

  1. This method does not require planning sex as the protection is available 24/7.
  2. Taking daily PrEP becomes part of your routine and helps achieve better compliance.
  3. Even if you miss upto 2 tablets in a week, adequate protection is available.
  4. It offers protection for all types of sexual contact (anal, vaginal, frontal).

Option 3: On-Demand

  1. First dose: Take 2 tablets 2 to 24 hours before sex
  2. Second dose: Take 1 tablet 24 hours after sex
  3. Third dose: Take 1 more tablet 48 hours after sex

Things to keep in mind with this method:

  • It is essential that all 4 tablets are taken to ensure protection.
  • If someone becomes sick after taking any of the 3 doses, the efficacy of the drugs can get threatened, and be at risk of being compromised.
  • It works for anal sex, but not for vaginal or frontal sex.
  • This method requires a degree of planning to ensure you have access to the tablets to hand, and being in a position to have 2-24 hours between taking tablets and having sex.
  • It also requires a little more discipline in order to take the tablets at the recommended times as per schedule.

What tests will I need after starting PrEP?

The following tests are recommended to monitor the safe and successful use of PrEP:

  1. A HIV blood test every 3 months
  2. A urine test to rule out any abnormality in the kidneys every 3 months
  3. An STI screen (if there is a risk of getting infection) every 3 months
  4. A blood test to rule out any abnormality in the kidney function (every 12 months)

Can I take a break from PrEP?

Yes. PrEP is useful as long as you are at risk of catching the infection. If your circumstances change and you are no longer at risk of HIV, you can come off these tablets.

And of course, you can go back to PrEP when your circumstances change and your risk of HIV has become high again. However, it is important that you have an HIV blood test before restarting your medication.

How does PrEP work?

Each PrEP tablet contains 2 active drugs which together produce enough levels of these drugs in the blood and body fluids. These drugs inhibit HIV-1 reverse transcriptase. As a result, when the person on PrEP comes into contact with HIV, the virus is not able to survive.

How effective is PrEP?

When taken as prescribed, PrEP is more than 99% effective at preventing HIV infection. However, in reality many people do not take the PrEP consistently and this can reduce its efficacy.

Is generic PrEP any less effective?

HIV PrEP medications have equal efficacy, whether they are generic or branded.

Sometimes patients report new side effects or a different taste when they are switched from branded to generic medications but this should not alter the efficacy.

It is important to note that most generic medications available by online pharmacies are meant for sale in the country of their origin and do not have the same level of quality assurance and recourse to recall and drug safety surveillance as the medications available through the legal route in the UK.

What if I miss a dose of PrEP?

  • If you missed a dose for less than 12 hours:
    Take the missed dose immediately, and take the next dose on scheduled time.
  • If you missed a dose for more than 12 hours:
    Don’t take the missed dose, and take the next scheduled dose on time. 
  • If you vomit within 1 hour of taking PrEP:
    Please take another tablet.
  • If you vomit more than 1 hour of taking PrEP:
    Please DO NOT take another tablet.

What are the common side effects?

Most patients taking PrEP experience no side effects. Occasionally, nausea and headache can occur which disappears after a few days of use.

Decrease in kidney function can rarely be seen and this tends to disappear after stopping the medication. Mild thinning of the bone can sometimes occur but its clinical significance is not known.

If you are concerned about any side-effects before starting these medications, we will discuss this in the initial consultation.

I have some kidney problems. Can I still take PrEP?

Many patients with mild kidney problems can still take PrEP. However, your safety and suitability for PrEP will be decided after review of your medical condition and checking your kidney function with a simple blood and urine test at the baseline. In such patients follow-up blood tests may be needed to detect a change in kidney function.

Can PrEP be used in elderly?

Yes. PrEP can be used at any age. However, decreased kidney function is common over the age of 65 years. This will be discussed during your initial consultation, before you start PrEP.

Should I take PrEP with food?

PreP medications can be taken with or without food. However, in order to optimise the absorption of tenofovir, it is recommended that PrEP should preferably be taken with food.

The tablet can be dissolved in approximately 100 mL of water, orange juice or grape juice and taken immediately.

Can I drink alcohol with PrEP?

Yes, you can drink alcohol with PrEP.

Do I need to be on the PrEP trial to take PrEP?

No, you don’t need to be on the PrEP trial to get PrEP from us.

How long can I take PrEP for?

You can take PrEP for as long as you need it. Using PrEP on a long term basis does not affect your health as long as you have regular urine and blood tests as per the recommendations. The medications used for PrEP have been used in HIV patients for more than 15 years, and are considered safe for long term use in most people.

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Page reviewed by Dr. Manoj Malu (Clinical Director)

Last reviewed date: 21 April 2020
Next review due: 21 April 2023

Whilst this content is written and reviewed by sexual health specialists, it is for general guidance only. It is not intended to replace the advice of your clinician.