What’s the difference between PrEP and PEP for HIV prevention?

PrEP and PEP are two ways to use anti-HIV medications as ‘prophylaxis’, in other words as prevention. They work in different ways.

PrEP stands for pre-exposure prophylaxis. PEP stands for post-exposure prophylaxis.
As indicated by ‘pre’, you start to take it before you may be exposed to HIV. As indicated by ‘post’, you start to take it after a single event that may have exposed you to HIV.
PrEP is designed to be used in a planned way, on an ongoing basis. PEP is used in emergency situations.
Most people take PrEP once a day, every day. Some people can use ‘event-based’ dosing, which involves taking it before sex and then for two days afterwards.

PEP is a four-week course of drugs, taken once a day during that time. It is best to start PEP within 24 hours of exposure to HIV, but certainly within 72 hours.

There are two drugs in PrEP. They are usually combined in a single tablet. There are three drugs in PEP – usually the same two that are taken for PrEP, plus a third one. The third drug works in a different way to the first two (it from a different drug class). The three drugs are usually provided in two tablets.

There’s more information on another page.

There’s more information on another page.


If you are taking PEP now and you think you might need protection again in the coming weeks and months, you can talk to your doctors about switching to PrEP at the end of the course.

And if you have needed PEP sometime in the past, especially if you’ve needed it more than once, it’s worth thinking about whether PrEP might be a good option for you going forward.

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