General Health

HIV PrEP — Pre-Exposure Prophylaxis

PrEP is daily or on-demand medication that dramatically reduces the risk of HIV infection in people at higher risk.

Updated: 4 min read

Overview

PrEP (pre-exposure prophylaxis) is one of the most significant advances in HIV prevention since condoms. When taken correctly, it reduces the risk of HIV infection through sex by over 99%. Combined with regular testing and condom use, PrEP has transformed HIV prevention for people at ongoing risk.

PrEP is not a treatment for existing HIV — it is a prevention tool for people who are HIV-negative. It requires a prescription and regular medical monitoring, but is widely available through sexual health clinics and GP services in many countries.

How PrEP Works

The standard PrEP medication (tenofovir disoproxil fumarate / emtricitabine — sold as Truvada or its generics) is an antiretroviral combination. The drugs accumulate in rectal, vaginal, and cervical cells and in the bloodstream, creating concentrations high enough to block HIV replication if the virus enters the body.

To be fully effective, PrEP needs to reach protective levels before exposure:

  • Receptive anal sex: full protection with 7 days of daily dosing
  • Vaginal sex or other routes: full protection with 21 days of daily dosing

For this reason, starting PrEP in advance of expected exposure is essential.

Who PrEP Is For

PrEP is appropriate for HIV-negative people who are at substantial ongoing risk. Your sexual health clinic will assess your risk. PrEP is commonly recommended for:

  • Gay, bisexual, and other men who have sex with men (MSM) with multiple or concurrent partners, or recent STI diagnosis
  • Trans women (daily PrEP recommended over on-demand)
  • People with a regular HIV-positive partner who is not virally suppressed, or whose status is unknown
  • People who inject drugs and share equipment
  • Sex workers
  • Heterosexual people with multiple partners in high-prevalence settings

PrEP is not needed if you consistently use condoms with all partners and test regularly, but for those at ongoing risk, PrEP provides an additional, highly reliable layer of protection.

Regimens

Daily PrEP

One tablet taken at the same time each day, regardless of sexual activity. Recommended for:

  • Anyone having frequent or unpredictable sex
  • Trans women (daily dosing maintains higher protective levels)
  • People using PrEP with injecting drug use

Event-Driven PrEP (2-1-1)

  • 2 tablets taken 2–24 hours before sex
  • 1 tablet 24 hours after the first dose
  • 1 more tablet 48 hours after the first dose

Effective for MSM who have sex less frequently and can plan in advance. Not validated for vaginal sex or injecting drug use.

Getting PrEP

UK: PrEP is available free on the NHS through sexual health clinics in England, Scotland, and Wales. You do not need a GP referral.

Australia: PrEP is available on the PBS (Pharmaceutical Benefits Scheme) at subsidised cost with a prescription.

USA: Truvada and generics are available by prescription. Many health insurance plans cover PrEP; the Ready, Set, PrEP programme provides free PrEP to qualifying uninsured individuals.

Other countries: Access varies significantly. Contact local HIV organisations or sexual health services for country-specific guidance.

Monitoring While on PrEP

PrEP care involves regular check-ups — typically every 3 months:

  • HIV test (to confirm continued HIV-negative status)
  • STI screening (chlamydia, gonorrhoea, syphilis, and hepatitis)
  • Kidney function test (to monitor for tenofovir effects)
  • Review of any side effects or concerns

These appointments are an important part of PrEP safety and are where any sexual health questions can also be addressed.

What PrEP Does Not Do

  • Does not treat HIV — if you are already HIV-positive, PrEP has no benefit and a different treatment is needed
  • Does not protect against other STIs — use condoms for additional protection
  • Is not emergency HIV prevention — for exposures that have already occurred, PEP (post-exposure prophylaxis) may be effective if started within 72 hours

When to Seek Care

See a sexual health clinic if:

  • You think you may be at ongoing risk of HIV
  • You have had unprotected sex with someone of unknown HIV status
  • You have been exposed to HIV in the last 72 hours (for PEP assessment — do not delay)
  • You are currently on PrEP and develop symptoms of illness or notice changes in urine output

Further Reading

Educational only — not a substitute for professional medical advice. Sexual health clinics provide confidential assessment and PrEP access.