Examples of event-based 2:1:1 and 2:7 dosing

The following examples show different doses for on-demand dosing.

1. Event-based 2:1:1 dosing: sex once

2:1:1 dosing can be used by anyone having insertive sex or receptive anal sex.

If you might have sex on Thursday take a double dose at least two hours before you have sex.

Then take a single pill for the next two days. This should be roughly 24 hours and 48 hours after the first double dose.

These times can be approximate. You still get good protection even if you have sex earlier or later than planned. Even if the pre-dose is only just before or even after sex, some PrEP is always better than none.

If you have sex several times over a few days, keep taking a pill each day. Continue for two days after the last day that you have sex.

2. Event-based 2:1:1 dosing: more sex!

If you have sex over a few days, keep taking a pill each day. Continue for two days after the last day you have sex.

If you have sex over several days continue to take a single pill every day you have sex at around the same time.

Then after you stop having sex, take daily PrEP for the next two days. 

If you start PrEP but then don’t have sex – and you have no plans to have sex – there is no need to keep taking PrEP. 

3. Event-based 2:7 dosing

2:7 dosing is sometimes needed by cis women and trans and non-binary people having receptive vaginal/frontal sex.

If you are a cisgender woman, or are transgender or non-binary, having receptive vaginal or frontal sex might need daily PrEP to continue for seven days. 

This is for situations when you didn’t take at least four doses of PrEP the previous week.

Start with a double dose before sex and then take daily PrEP for seven days after sex, at roughly the same time each day.

Last updated: 1 February 2024.