Event based PrEP


Event-based PrEP offers flexible protection.

Six Easy Steps

Event-based PrEP (EBP) offers flexible protection against HIV, whether that’s for a single fuck, a dirty weekend, or fucking every day or two for a fortnight or longer.

With EBP the key is improvising within guidelines. You need to follow the guidelines, but also apply them to your own changing circumstances. As long as you keep doing EBP according to the guidelines, you’re protected.

This resource shows you the six easy steps to follow for flexible protection.

It has been designed for guys (including trans guys) who are thinking about using event-based PrEP (EBP) for HIV protection during anal sex. It provides plain language information to inform the conversations you may have with friends and partners – and doctors – about EBP.

This resource assumes you understand the basics of PrEP. If you’re not familiar with PrEP, we recommend starting here.


EBP only provides protection against HIV during anal sex. If you need protection for frontal/vaginal sex, daily dosing is for you.

Also, there’s evidence suggesting feminising hormones may reduce rectal concentrations of PrEP. Again, daily PrEP works just fine for trans women!


In the 24 hours before your first fuck, take a start-up dose of two pills.


Always leave at least two hours between taking a start-up dose and fucking. 

(You don’t need to do this with follow-up doses.)


24 hours after your start-up dose, start taking one pill each day – around the time you took the start-up dose.


Take a follow-up dose each day until two days after your last fuck.


If another fuck comes along less than 7 days after finishing up, you can restart by taking one pill instead of two. The lead-in, follow-up and finish-up rules apply as normal.


24 hours after your start-up dose, start taking one pill each day – around the time you took the start-up dose.


If you miss a dose or mess up the timing, continue with the follow-up doses and contact your sexual health clinic for advice on your options. This may include starting PEP – see below for more details about risk.

About event-based PrEP


Studies show that EBP is just as effective as daily dosing.

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In 2010 we learned that taking a daily dose of an HIV medication can protect people from getting HIV. This is known as PrEP (pre-exposure prophylaxis). A study called iPrEx showed that PrEP works – as long as you take it as prescribed. A follow-up study found there were no HIV infections among participants who took at least four pills per week.

Some folks asked: what about only taking pills when you’re having sex? Another study called IPERGAY answered that question. Two hundred guys in France and Montréal took pills before and after sex. (We’ll show you the timing schedule below!) Known as ‘event-based’ dosing, this approach proved to be just as effective as daily dosing. Just like daily dosing, event-based dosing (EBD for short) only works when you take it.

As it happens, participants in the IPERGAY study were having a lot of sex. At least half were taking four pills or more per week – about the same amount that proved 100% effective with daily dosing. So the IPERGAY team also looked at data from folks having less ‘busy’ months, when they were using event-based PrEP less often. Result: EBP was still just as effective as daily dosing.

In some parts of the world EBP is also called 2-1-1 PrEP.


The EBP approach involves thinking ahead, so it works best for people who can generally anticipate when sex is going to happen.

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You need to leave at least two hours’ lead-in before taking the start-up dose and having sex – enough time for the pills to start working.

For example, if your sex life involves the occasional binge or blowout, like a sauna visit after work or a party weekend, or if you generally arrange hook-ups a couple of hours before meeting up, EBP may be an option for you to consider.

Other reasons for using EBP might include wanting to get more bangs for your bucks – reducing the overall cost of PrEP by only taking pills when you’re actually having sex. A small number of people experience continuing side effects during daily dosing, and using EBP might help you reduce the amount of time you experience those side effects.

If you are thinking of doing EBP, you also need to consider:

  • Do you normally have at least two hours lead-in before sex?
  • Are you generally pretty good at taking pills on time?
  • Can you handle the additional requirements of EBP?


You need all the same check-ups when doing event-based PrEP. 

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When you start PrEP, you get tested for HIV and STI (sexually transmitted infections) and a kidney function test. It’s important to check that you don’t have HIV before you start PrEP, because the two drugs used for PrEP are not enough on their own to suppress HIV infection, and taking PrEP when you have HIV can limit some of your options for future treatment.

You also need follow-up STI check-ups every three months, because PrEP only prevents HIV. Regular STI testing and treatment also help reduce the prevalence of STIs in the community. You should get vaccinated for hep A and HPV (if you are eligible), and it’s important to check that you don’t have hep B before using PrEP.

If you are thinking about, or have already started doing EBP, we recommend letting your sexual health clinic know so that they can support you. We have included key references and guidelines below, in case your clinic is not convinced about EBP.

Making EBP work for you


Many of the resources for daily dosing list tips and strategies that work for EBP as well. Here are some recommendations for EBP in particular. If you find these ideas don’t work for you go ahead and figure out what does and remember to share what you learn with your friends, health staff and the PrEP community on social media.


When you take your start-up dose, set a daily alarm on your phone at the same time of day. Label it as something that will remind you to take your next dose. Turn the alarm off when you finish up.


Buy a 7 or 14 day pillbox that you can carry with you. Each day you have a fuck, check there are pills in slots for another two days. (When you get to the last slot in the pillbox, just ‘wrap around’ to the starting slot.)


You might like to try an app like Loop Habit Tracker (for Android) or Productive (for iOS). This allows you to track when you take your start-up dose, the days you’ve fucked, and your follow-up doses, so you know when you can finish up (or restart). If apps aren’t really your thing, you could jot notes in a paper diary or calendar, or even on your arm.


A party weekend — which could be a dance party or chemsex — might change your usual routines for eating and sleeping. Remember to take your pills to parties and play sessions. Bring a couple of extras in case you’re out longer than you expected. If you take your start-up dose late on Friday night, and by Monday you’re heading for an early night, take your follow-up dose before you go to bed.


Some people find that taking two pills at once is a challenge. It is okay to take the two pills at different times, e.g. the first one at lunch and the next one at dinner. Just make sure you leave two hours between the second pill and having sex – and take your first follow-up dose around 24 hours after the first pill.

Finding information and support

If you’re ever unsure how to proceed, ask for assistance right away!

  • Staff at your sexual health clinic should be able to answer questions about different ways of using PrEP.
  • Talk it over with friends to check your understanding of the way EBP works. 
  • Your local sexual health organisation may have educators who can provide answers.
  • Ask a question in one of the many great Facebook groups for PrEP users (see links below).
  • You can find evidence on event-based PrEP written in plain language on sites like AIDSMap.

Clinical guidelines

In July 2019, the World Health Organisation concluded that national PrEP guidelines and protocols for men who have sex with men should include EBP as an option. Clinical guidelines in many parts of the world including Australia and the UK give advice on supporting patients to make an informed choice between daily dosing and EBP. 

A word about PEP and risk

PEP is short for post-exposure prophylaxis, where you take anti-HIV medication daily for 28 days. You might consider PEP if you missed multiple doses on the EBP schedule. 

U=U means Undetectable = Untransmittable, and it sums up the scientific evidence that shows a person with an undetectable viral load poses zero risk of HIV transmission

This is something to keep in mind in case you ever have to consider going on PEP. 

The decision to start PEP is made on the basis of your risk exposure. U=U means that positive status does not mean ‘risky.’ Sex with partners with an undetectable viral load is not a risk exposure.

The highest-possible risk is sex with a person in the first few weeks of HIV infection. They may not have any symptoms, and still believe they are HIV-negative, but their viral load is extremely high. 

So if you’ve missed doses and you know your HIV-negative partners have missed doses – for example, running out of pills on a party weekend – talk to your sexual health clinic about starting PEP.

Resources and evidence

The rest of the Prepster site provides all-round resources for information and advocacy tools

IWantPrEPNow has a great summary of the different PrEP approaches, including daily dosing, on-demand (event-based), holiday dosing and time-based (T & S) dosing 

Three great Facebook groups include PrEP Access Now (Australia) and PrEP Facts (US and global) and PrEP In Europe (Europe) 

AIDSMap.com reports in plain language on all the publications from PrEP studies, including the IPERGAY study which demonstrated event-based PrEP is just as effective as daily dosing

GRUNT is an Australian-made sexual health resource for trans men who have sex with men

About this project

This project was developed from an original independent community initiative developed by Daniel Reeders, an experienced HIV campaign strategist, in partnership with Dr Darren Russell, an HIV and sexual health physician who has first-hand experience supporting patients using event-based PrEP in France. The target audience for the project is people who are considering or already using event-based PrEP – in marketing terms, the ‘innovator’ and ‘early adopter’ segments, who are willing to experiment, have a greater appetite for information, and who often become informal educators for friends, partners, clinicians and online communities. 

The original project has been redeveloped in collaboration with Daniel Reeders with Will Nutland (PrEPster) and Greg Owen (iwantPrEPnow) and adapted for a UK and international audience.



Executive producer 
Daniel Reeders (DNM Consulting and the Bad Blood blog)

Samuel Leighton-Dore (website and Facebook and Instagram)

Animator and sound design
Gisele Nour (website)

Alex Fitch (NeedleDrop)

Thanks to Pierre Nedd for assistance with sound editing in the adapted version.