On-Demand (Event-Driven) PrEP

‘On-demand’ (also called “event-based” or “event-driven”) use of PrEP refers to taking PrEP only when we are going to have sex, rather than taking it every day at the same time.

On demand PrEP might work well for you if:

  • Plan the times that you are are having the kinds of sex that might pass HIV (eg: fucking/anal);
  • Don’t have sex very often (e.g. once per month)
  • Are not taking daily PrEP, and are planning to attend a sex, or play party and are unsure what kinds of sex you will be having.
  • Are prepared to remember to take the medication according to a strict schedule;
  • Do not have the kind of sex that might pass HIV more than once or twice per week;
  • Have consulted with a doctor about on-demand PrEP.


Taking PrEP on-demand…

Two pills of PrEP two to 24 hours before anal sex, followed by one pill daily including 48 hours after the last episode of anal sex.

Broken down another way, using on-demand use of PrEP means:

  • 2 – 24 hours before sex: 2 PrEP pills
  • 1 day (24 hours) after first 2 pills : 1 PrEP pill
  • 2 days (48 hours) after 3rd pill: 1 PrEP pill
  • No more sex? No more PrEP pills.
  • Still having sex with the same higher chance of HIV transmission? 1 PrEP pill every day until 2 days after you stop having such sex.


On-Demand PrEP’s effectiveness…

On-demand use of PrEP was first researched in the ‘Ipergay’ study. This study showed that PrEP taken on-demand is highly effective at preventing HIV transmission for anal sex.

PrEP taken on-demand does not effectively reduce the chance of passing HIV for front hole sex. But taken daily PrEP is still highly effective for reducing transmission from front hole sex.


PrEP on-demand in Canada…

PrEP on-demand has been recommended for use in other countries but Health Canada has only approved daily PrEP (PrEP taken every day). However, a physician in Canada can still prescribe PrEP for on-demand use following national or provincial clinical guidelines.

Because on-demand PrEP is newer and many doctors have less experience with it, your doctor may recommend daily PrEP.

It is important to have an open conversation with your doctor about the ways you have sex in order to establish a safe and satisfying way of on-demand PrEP use. If you feel that on-demand PrEP is right for you, discuss this with your doctor.  You could also refer them to provincial PrEP guidelines so they can familiarize themselves with this method.