Anti-infective
HIV PrEP
Pre-exposure prophylaxis — Medicine taken by HIV-negative people to prevent catching HIV — highly effective when taken correctly.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
Quick answer
What is HIV PrEP?
PrEP is anti-HIV medicine taken by HIV-negative people to greatly reduce their chance of catching HIV. Taken correctly it is highly effective.
- How it works: PrEP keeps protective levels of anti-HIV drugs in the body so that, if HIV enters, the virus cannot establish an infection and take hold.
- In practice: In practice PrEP (pre-exposure prophylaxis) is medicine taken by people who do not have HIV to stop them acquiring it, and it is highly effective when taken as advised.
What it is
PrEP is anti-HIV medicine taken by HIV-negative people to greatly reduce their chance of catching HIV. Taken correctly it is highly effective. It is provided through sexual-health services with regular testing and monitoring.
How it works
PrEP keeps protective levels of anti-HIV drugs in the body so that, if HIV enters, the virus cannot establish an infection and take hold. It blocks the early steps the virus needs to copy itself — which is why it has to be present at the time of exposure, and so depends on taking it consistently.
In practice
In practice PrEP (pre-exposure prophylaxis) is medicine taken by people who do not have HIV to stop them acquiring it, and it is highly effective when taken as advised. It is for people at higher risk of HIV exposure, and the practical themes are eligibility, adherence and monitoring. Before starting, an HIV test confirms the person is negative (PrEP alone is not enough treatment for established HIV and could cause resistance), and kidney function, hepatitis B status and other sexually transmitted infections are checked. It can be taken as a daily tablet or, for some, as an "on-demand" (event-based) schedule around sexual activity — the right approach depends on the individual and the type of exposure. Ongoing care means regular HIV and STI testing and kidney monitoring while on it. A crucial counselling point is that PrEP prevents HIV but not other sexually transmitted infections or pregnancy, so condoms and other protection still matter. It is a powerful prevention tool that works only if taken consistently around the times of risk, and it is started and stopped according to need under a sexual-health service.
Examples
Practical use
How to take it & use it well
- Take it exactly as agreed with your clinic, either every day or around the times of risk, as it only protects you when taken consistently in the way you have been shown.
- Make sure you are confirmed HIV-negative before you start and test regularly while taking it, as starting or continuing with undetected HIV can lead to resistant virus.
- Link your doses to a daily routine and use reminders, since gaps in cover are what allow HIV to take hold.
- Remember it protects only against HIV, so continue to use condoms to guard against other sexually transmitted infections and pregnancy.
- Attend your regular clinic checks, which include HIV testing and looking after your kidneys and hepatitis B status.
- Never stop or change how you take it on your own, and tell the clinic if your circumstances or risk change so your plan can be adjusted.
Common uses
- Preventing HIV in people at higher risk
- Daily or event-based (on-demand) prevention
- Part of combination HIV prevention with testing and STI care
Monitoring
- Regular HIV and STI testing
- Kidney function and hepatitis B status
- Adherence and whether daily or event-based suits best
Weighing it up
Advantages & disadvantages
Advantages
- Taken correctly, it is highly effective at preventing HIV in people who are HIV-negative.
- It gives people control over protecting their own health, alongside other safer-sex measures.
- It can be taken either daily or, for some people, around the times of higher risk.
- It is well studied, with a strong record of safety and effectiveness when used as directed.
- It allows people at higher risk to reduce worry and stay HIV-negative.
Disadvantages
- It only works if taken consistently, so missed doses leave gaps in protection.
- It does not protect against other sexually transmitted infections or against pregnancy.
- It needs regular HIV testing, because taking it with undetected HIV risks creating resistant virus.
- It can affect the kidneys in some people, so monitoring is needed.
- Some people get early side effects such as nausea or headache, which usually settle.
Key safety principles
What to watch for
- Confirm HIV-negative before starting and test regularly — PrEP is not enough to treat established HIV and could cause resistance.
- Prevents HIV but NOT other sexually transmitted infections or pregnancy — condoms and other protection still matter.
- Needs kidney monitoring and hepatitis B check; works only if taken consistently around the times of risk.
Key interactions
What to avoid or check alongside
- It must only be taken by people who are HIV-negative, confirmed by testing before starting and repeated regularly, or resistant HIV can develop.
- It does not protect against other sexually transmitted infections or pregnancy, so condoms and other measures are still important.
- Your kidneys are checked before and during treatment, and your hepatitis B status is checked, as stopping can affect hepatitis B.
- It only works when taken consistently around the times of risk, so honest discussion with the clinic about your pattern matters.
- Tell the clinic about other medicines and supplements you take, as a few can add to the strain on the kidneys.
Patient & carer advice
- Take it as advised — it only protects if it is in your system around the time of risk
- It does not protect against other STIs or pregnancy, so keep using condoms
- Keep up your regular HIV and kidney checks at the clinic
Use with
Related clinical calculators
Dose and risk decisions for this class often depend on renal function, weight or bleeding/stroke risk. These tools help:
Answers
HIV PrEP: frequently asked questions
Who is PrEP for?
PrEP is for people who are HIV-negative but at higher risk of getting HIV, to help prevent infection. You need to be confirmed HIV-negative before starting and tested regularly while taking it. It is taken either every day or, for some people, around the times of risk, as agreed with your clinic.
Does PrEP protect against other sexually transmitted infections?
No. PrEP only protects against HIV. It does not guard against other sexually transmitted infections such as gonorrhoea, chlamydia or syphilis, and it does not prevent pregnancy. Using condoms alongside PrEP gives you protection against these as well.
Why do I need regular HIV tests on PrEP?
Because PrEP is not a full HIV treatment, taking it while unknowingly having HIV can let the virus become resistant, which limits future options. Regular testing confirms you are still HIV-negative so PrEP keeps working safely. It also lets your clinic check your kidneys and hepatitis B status.
What happens if I miss doses?
PrEP only protects you when taken consistently in the way you have been shown, so missing doses leaves gaps where HIV could take hold. Use reminders and a routine, and if your dosing slips or your circumstances change, talk to your clinic so your protection and plan can be reviewed.
Can PrEP affect my kidneys?
It can affect the kidneys in some people, which is why your clinic checks them before you start and during treatment. Most people have no problem, and any change is usually picked up early. Tell the clinic about other medicines you take, as some add to the strain on the kidneys.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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