On Demand PrEP or Event Based Dosing

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Page last reviewed 20.4.2022

The most common way to take PrEP is to take it daily, which means one pill taken at approximately the same time every day. On-demand PrEP using is shown to be highly effective for gay and bisexual men. PrEP on an event bases (on-demand) is currently only recommended for cis-men who have sex with men. This option might be most appropriate for people who have fewer HIV-related risk situations (sex without condom) and those who have sex less than twice a week and those with predictable sex lives.

How to take PrEP on event basis?

On-demand PrEP is also known as event-based PrEP or PrEP 2-1-1. It involves taking two tablets 2 to 24 hours before engaging in sex, taking a single tablet 24 hours after the first two, and another tablet 24 hours after that.

In the case you continue having sex more than one session:

  • Take two pills 2-24 hours before having sex
  • Then continue taking one pill each day at approximately the same time
  • Continue this until you have had 2 sex-free days.
An explanation as a diagram of how to use on-demand PrEP.
PrEP on-demand is just as its name suggests; you take it ‘on-demand’, or when you know you’re going to have sex. It requires less pills over a shorter period (before and after sex).