Event-based dosing

Start with a double dose (two pills) at least two hours before you are going to have sex.

However, instead of continuing to take daily PrEP you only continue for either two or seven days – depending on the type of sex you have.

If you continue having sex for several days, just keep taking a daily pill. Then continue daily PrEP after the day you last have sex for either either 2 or 7 days.

Event-based dosing is just as effective as daily PrEP. It is often used by people who have sex less often than once a week and who usually know when they might be likely to have sex.

Event-based dosing needs fewer pills, but it can’t be used if you have hepatitis B.

2:1:1 dosing

2:1:1 dosing involves starting with a double dose and then taking daily PrEP for two days after sex. Each dose should be roughly 24 hours after the previous one.

2:1:1 dosing can be used by anyone for anal sex (if you are the insertive or receptive partner) or insertive vaginal/frontal sex. It can not be used for receptive vaginal/frontal sex.

2:7 dosing

2:7 dosing involves starting with a double dose and then taking daily PrEP for seven days after sex. Each dose should be roughly 24 hours after the previous one.

2:7 dosing needs to be used by cis women and trans and non-binary people who are having receptive vaginal/frontal sex.

The pre-dose is important for the highest protection when using event-based dosing. But if you miss or are late with the pre-dose, start with a double dose as soon as you can.