What is PrEP?

Pre-exposure prophylaxis (PrEP) is when people take an HIV medication to reduce their chance of getting infected while they are at risk of acquiring HIV.

The World Health Organization currently recommends the use of PrEP taken daily for both men and women who are at substantial risk of acquiring HIV (WHO, 2017). 

How well does PrEP work?

  • PrEP does not provide 100% protection, but it is highly effective and provides a great deal of protection against HIV. In some recent studies, PrEP has been shown to reduce the risk of HIV infection during sex by over 90% when used consistently.
  • Taking PrEP every day is recommended because daily use of PrEP is effective, safe and the most convenient approach. Daily PrEP use provides the highest amount of medication in the blood and body tissues and, thus, the highest level of protection. If you take PrEP daily, you may still be protected, even if you miss a dose once in a while.
  • Time is needed to build up protective levels of the medicine in the blood and other tissues. Additional HIV prevention should be taken for the first seven days when starting PrEP. Ways to lower risk during this period include: adopting safer sexual practices, such as not having vaginal or anal intercourse, or using condoms. It is suggested that PrEP should be continued for 28 days after the last potential exposure to HIV.

What are other ways to stay free of HIV?

There are a number of strategies to stay free of HIV infection. You should choose what best suits your own needs and personal situation. You may combine different ways of staying free of HIV, and you can change which strategies you use over time. Here are some of the other things you can do to protect yourself.

  • Male and female condoms (with lubricants) are effective when they are used consistently, with all sexual partners. Condoms also protect against other sexually transmitted infections and pregnancy.
  • If you have a partner who has HIV, treatment of his or her infection with antiretroviral therapy (ART) can nearly eliminate the risk of transmission. For your partner’s HIV treatment to protect you from HIV infection, your partner should have a viral load test that shows that their HIV has been suppressed to “undetectable” levels. If you have doubts about your partner’s adherence to HIV treatment or the result of his or her viral load test, it is best to protect yourself in additional ways.
  • If you inject drugs, it is recommended to use new or sterile injection equipment, whenever possible. This will prevent HIV transmission as well as other transmissible blood-borne infections such as hepatitis B and C.

What is the difference between PrEP and PEP?

  • Where Pre-exposure prophylaxis (PrEP) is a pill taken once daily in order to build up a level of medicine in your blood that prevents exposure to HIV from becoming an HIV infection, Post-exposure prophylaxis (or PEP) is antiretroviral medication that can be taken after you have an exposure to body fluids containing HIV. For PEP to work well, you must start PEP less than 72 hours after exposure. PEP, in the form of 2-3 pills daily, should be continued for 28 days after the exposure.

Do I need to use condoms while I am taking PrEP?

  • PrEP does not require the use of condoms to be effective. However, condoms provide additional protection against HIV and protect you from other sexually transmitted infections and unplanned pregnancies.
  • PrEP does not prevent sexually transmitted infections, such as syphilis, gonorrhoea, chlamydia and hepatitis. Condoms do provide protection against these other infections as well as against HIV, and so they protect your overall sexual health.
  • PrEP does not prevent pregnancy. When used consistently, condoms prevent pregnancy. There are many other ways to prevent pregnancy, including oral contraceptive pills and injectable hormones, implants, intrauterine devices and diaphragms. PrEP does not interfere with any contraceptive method.

When do I take PrEP?

  • WHO recommends that you take PrEP once a day every day. Daily use is safe and convenient and it provides the best protection against HIV.
  • Recent research suggests that taking PrEP on-demand (also known as event-based dosing), may be a suitable strategy for some people. It is important to know that on-demand PrEP dosing is only effective for preventing HIV during anal intercourse, and does not provide protection during vaginal intercourse. It is important that if you choose to take PrEP on-demand, that you make sure to take every dose.
  • A dosing schedule for taking PrEP on-demand (for protection during anal intercourse) is as follows:
    • take 2 pills 2 – 24 hours before sex
    • take 1 pill 24 hours later
    • take 1 more pill 24 hours after that
    • If you know you will be having sex over a period of multiple days, continue to take one pill every 24 hours until you have two sex-free days.
  • For more information on strategies for taking PrEP, including daily and on-demand, visit this helpful link: www.iwantprepnow.co.uk/how-to-take-prep/

How do I take PrEP?

  • PrEP is taken orally, and can be taken at any time during the day and at different times on different days.
  • It is helpful to link taking PrEP with something that you do every day.
  • PrEP can be taken with or without food.
  • PrEP can be taken when drinking alcohol or using recreational drugs.
  • PrEP can be taken if you are taking hormonal contraceptives, sex hormones or non-prescription drugs.
  • It takes about seven days of taking PrEP daily before there is enough medication in your body to provide protection against HIV.
  • Before you start PrEP, you will be tested to make sure that you do not have HIV. If the test finds that you have HIV, you will be linked to HIV treatment services.
  • While taking PrEP, you will need to be re-tested for HIV every three months to be sure that you remain free of infection.
  • A person’s risk for HIV infection may vary over time as circumstances change. For example, the break-up of a stable relationship may start a time of higher risk. These are what are sometimes called “seasons of risk”. You may choose to stop using PrEP at certain times and to start again as your situation changes.

Does PrEP have side effects?

  • Some people experience side-effects when starting PrEP. These may include abdominal bloating, softer/more frequent stools or nausea.
  • These symptoms are usually mild and go away in the first few weeks.
  • Strategies that some people find helpful to reduce stomach-related symptoms:
    • take the pill with food
    • take the pill at night before bedtime.


  • For a few people, PrEP affects how well their kidneys work. Your blood will be tested to measure kidney function before you start PrEP. If the test shows a problem, this kidney test may be repeated. If the test continues to show a problem, you will be referred for further testing. Once you start PrEP, the clinic providing your PrEP will offer you blood tests to monitor your kidney function. If your blood test shows a problem, you may be asked to stop taking PrEP for a while. Kidney function usually will quickly return to normal, and then you can restart PrEP.
  • PrEP can have a small effect on bone mineral density (how strong bones are). The change occurs in the first few months of PrEP use and does not continue after that. PrEP users do not experience more broken bones than is usual. If you stop taking PrEP, bone mineral density usually returns quickly to normal.

What if I want to become pregnant while taking PrEP?

  • You or your partner may want to become pregnant. If this is the case, please tell your doctor or nurse.
  • There are two main ways to safely have babies with a partner who has HIV (or if you might have HIV). These are:
    • Treatment of the partner who has HIV with antiretroviral therapy, and checking to make sure his or her viral load is suppressed.
    • Taking PrEP is a way to safely conceive a child with a partner who has HIV and is not virally suppressed on antiretroviral therapy or with a partner who has not been tested for HIV.


Can I keep taking PrEP while pregnant and breastfeeding?

  • In places with high HIV incidence, HIV infection can also occur at high rates during pregnancy and breastfeeding. The risk of passing HIV infection onto a baby is higher if the mother becomes infected while she is pregnant. The existing safety data support the use of PrEP in pregnant and breastfeeding women who are at continuing substantial risk of HIV infection.
  • If you are taking PrEP and you find out that you are pregnant, you may want to continue to use PrEP if you continue to be at risk for HIV infection.
  • You may also consider continuing to take PrEP while breastfeeding.

Content source: World Health Organisation, Centers for Disease Control & Prevention