PREP VS PEP: A CLEAR AND CALM GUIDE TO YOUR OPTIONS
🕓 Last updated: 23 December 2025
Two different tools, one for ongoing prevention and one for emergencies, and how to know which one fits your situation. If you are trying to time testing, read HIV window periods. If you are symptom-scanning, read HIV symptoms: separating fact from fear. If you want to see how we turn your details into a probability, read the risk calculator guide.
PrEP is for ongoing prevention before exposure. PEP is an emergency option after a specific worrying event.
PrEP is taken regularly by people who are HIV negative and want long term protection. When used consistently, it can reduce the risk of getting HIV from sex by about 99 percent.
PEP is a 28 day course of HIV medication that you start after a possible exposure. It should be started as soon as possible and always within 72 hours of the event.
PrEP is like wearing a seatbelt every time you drive. PEP is like an airbag that deploys in an emergency. Both are powerful tools, but they are used at different times. If your worry is mainly about a single encounter, you may also want the personalised risk assessment so you are not guessing.
When it comes to HIV prevention, you might hear the terms PEP and PrEP mentioned. They sound similar, and it is easy to get them mixed up, especially when you are already anxious about potential HIV symptoms or a recent scare.
It helps to think of them as two different tools in the same safety kit. One is for ongoing peace of mind, the other is for emergencies. Understanding the difference can make you feel more in control and less overwhelmed by what you should do next.
PrEP: For Ongoing Peace of Mind
PrEP, which stands for Pre Exposure Prophylaxis, is a medication you take to prevent HIV before you are exposed. It is designed for people who are HIV negative and want an extra layer of protection on an ongoing basis.
By taking PrEP as prescribed, either as a daily pill or as a long acting injection, you build up a level of medicine in your body that can block HIV if it enters your system during sex. When used consistently, PrEP is highly effective at reducing the risk of getting HIV. If your concern is mostly about one encounter that already happened, skip to PEP and then read window periods.
- Taken before sex to prevent HIV.
- Best for people who have ongoing risk and want continuous protection.
- Needs consistent use to reach full effectiveness.
- Can provide day to day peace of mind.
PEP: For After a Worrying Moment
PEP, or Post Exposure Prophylaxis, is an emergency option you use after a possible exposure to HIV. It is not meant for regular use. Instead, it is there for specific events that feel risky, for example a condom breaks, you have unprotected sex, or you share needles.
The most important part of PEP is timing. You must start the medication as soon as possible, and always within 72 hours of the exposure. The medicine is taken every day for 28 days. The earlier you start, the higher the chance it will prevent HIV from taking hold. If you are outside that 72-hour window, your next step is usually testing strategy, start with window periods.
- Taken after a possible exposure to HIV.
- Used as an emergency measure, not as a routine.
- Must be started within 72 hours, sooner is better.
- Requires a 28 day course of pills.
Easy way to remember:
PrEP: Pre, used ahead of time for ongoing protection.
PEP: Post, used after a specific event as an emergency back up.
If you are trying to understand how the actual act changes risk, see the guides on oral sex risk, female to male transmission, and circumcision and risk.
How Do I Know Which Is Right for Me?
The right option depends on your pattern of risk and what you want from your prevention plan.
If you feel that there is ongoing risk in your life, for example regular sex with partners whose HIV status you do not know, PrEP can be a strong choice. It can act as a steady foundation that is always there in the background. If a partner is known to be undetectable, that changes the equation dramatically, see U=U and viral load.
If you do not use PrEP and you have just had a specific experience that scares you, PEP is the route to consider. The key is to act quickly. If you want to replace vague fear with a structured estimate, use the confidential assessment and read the calculator guide to understand how the number is derived.
Testing Still Matters
Both PrEP and PEP sit alongside, not instead of, HIV testing. PrEP users need regular tests to confirm they remain HIV negative and to monitor overall health. People who have taken PEP are usually advised to test at the start, again after the course, and sometimes at later time points, depending on local guidelines.
Understanding HIV test window periods can help you plan these checks so that your results are reliable. This combination, prevention plus properly timed testing, is what truly turns ongoing worry into a clear, manageable plan. If you are stuck on symptoms, remember symptoms cannot confirm HIV, only testing can, see symptoms vs fear.
Moving from Worry to Confidence
Feeling anxious about HIV is common, especially after a scare. The most useful way to handle that anxiety is with structure and facts. By understanding how PrEP and PEP work, you are not just replaying what happened in your head. You are working with clear options.
You can ask yourself three simple questions. Was this a one off event or part of a pattern, how recently did it happen, and what tools are available where I live. Once you know the answers, you can decide whether you need PrEP, PEP, testing, or simply reassurance. If the goal is a clean probability plus next steps, start with the risk assessment.
Use our confidential assessment to get a personalised transmission probability and testing timeline based on your exact encounter, your role, and your country. Many people find that seeing a number and a step by step plan makes it much easier to breathe again. If you want to understand the logic behind the output, read the risk calculator guide.
Get my confidential risk assessmentFrequently Asked Questions
Yes. PEP reduces the chance of HIV taking hold, but follow up testing is still needed to confirm the outcome. For timing, use window periods.
PEP is designed as an emergency option, not as a regular strategy. If you find that you are needing PEP often, that is usually a sign that you might benefit more from starting PrEP, which provides ongoing protection and can simplify your prevention plan.
PrEP is very effective at preventing HIV, but it does not protect against other sexually transmitted infections or pregnancy. Many people choose to use PrEP together with condoms so that they are protected on several fronts at once. If your worry is mainly about HIV specifically, it can help to understand how viral load changes risk, see U=U.
The safest approach is to speak to a doctor or sexual health clinic as soon as possible and let them help you decide. If you want structure before that conversation, use the assessment and read how the calculator works.
In many cases, yes. People who needed PEP for a specific event often have similar risks in the future. Your clinic can advise you on when and how to transition from PEP to PrEP so that your protection remains continuous.
Using PrEP or PEP is a sign that you are taking your health seriously. Sexual health clinics work with these medicines every day and are trained to provide care without judgement. If anxiety is the main issue, the best move is often a clear testing plan, see window periods, and a grounded risk estimate, see the assessment.