Examples for on-demand dosing

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

1. On-demand dosing: If you have sex once a week


Fig 1. On-demand dosing if you have sex once a week

If you think you might have sex on Friday or over the weekend, you could take two pills on Thursday, i.e. at 10 pm.

If you have sex on Friday at 7 pm, then you would take a single pill on both Friday and Saturday at around 10 pm.

These times can be approximate. You still get good protection if you took the Thursday dose at 6 pm and had sex on Friday at 11 pm. Even if the pre dose is only two hours before sex, or just before sex, or even after sex, some PrEP is always better than none.

From having sex once, on-demand dosing involves four pills.

2. On-demand dosing: Sex several times over a few days


Fig 2. On-demand dosing If you have sex several times during a week.

Take your double dose as usual 2 to 24 hours before sex.

If you have sex on Saturday, and a few times until Sunday at 1 am, continue to take a single pill every day at around the same time until you have had two doses after sex. Using the example above, your last dose would be on Monday.

If you don’t have sex on Saturday or Sunday, but might still have sex on Monday, you only need to continue with a single pill on Saturday, Sunday and Monday. This is because you already have good levels of PrEP drugs. In this case you would continue taking PrEP daily until you have had two sex-free days, i.e. until Wednesday (seven pills).

If you start PrEP but then don’t have sex on Saturday, and have no plans to have sex on Sunday or Monday, there is no need to take PrEP on any of these days.

If you didn’t continue with daily PrEP on Saturday and Sunday, you need to restart with a double-dose to get best drug levels again.

If there are less than seven days between the end of one on-demand dosing period and the beginning of another, you only need to take one single PrEP tablet when you restart.

If it is more than seven days since your last PrEP dose, start again with a double dose of two pills.

Last updated: 1 November 2022.