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  • Writer's picturePAN [PrEPaccessNOW]

How Effective Is PrEP?

PrEP works incredibly well at preventing HIV. In fact, it is the single most effective tool at preventing HIV for an HIV negative person.

PrEP provides almost 100% protection against HIV. How effective PrEP is depends on a few things, like how often you take it. If you miss doses of your PrEP, the level of protection may decrease.

If you are a cisgender man taking PrEP and you miss a dose you’re still going to have great levels of protection. In studies of PrEP where people took their PrEP 4 days or more per week – no one acquired HIV. [2]


Taking your PrEP every day is much more important for cisgender women, and trans people. There are a number of reasons for this such as the different body tissues in the rectum, vagina, neo-vagina, or front-hole.

Put simply, if you’re a cis women or person of trans experience – PrEP works – it’s just more important to take your pill every single day.


For cisgender men who have sex with men - both Daily PrEP and On Demand PrEP provide almost 100% protection.

For all other people, including cisgender women and trans people - Daily PrEP is the way to go, and it provides incredibly high levels of protection as well.


How long you need to take PrEP before sex depends on who you are again. Check out How to Take PrEP for more.

For Cis Men Into Men

For Cis guys into other guys, all you need is 2 hours start time to get protected. Start by taking 2 PrEP pills at once, at least 2 hours before sex - then you're on your way! Then, just keep taking your PrEP every day - or use carefully timed doses to use On Demand PrEP.

When stopping PrEP, cis guys into guys need to have two days where you took a PrEP pill after the last possible HIV exposure. Check out How to Take PrEP for more.

For Everyone Else

When starting PrEP for cisgender women cisgender men who don't have sex with men, and trans people, it takes at least seven days of taking your PrEP every day to reach high levels of protection against HIV.

Once you have 7 days of constant PrEP use under your belt – simply keep taking it each day for the length of time you wish to be protected by PrEP.

When stopping PrEP, people should continue using PrEP for another seven days after the last possible HIV exposure. So 7 days to start, and 7 to finish. Check out How to Take PrEP for more.

- - - - - - - - - - Got feedback? Got a question that we haven’t covered? We’d love to hear it!

Just e-mail with your question or comment, and please include the question title you’re writing about and be as detailed and specific as you can with your comments.

If possible, please provide links to any relevant sources. - - - - - - - - - -


[1] Emtricitabine-Tenofovir Concentrations and Pre-Exposure Prophylaxis Efficacy in Men Who Have Sex with Men (iPrEX)

[2] Zero HIV Infections When PrEP Is Taken 4 or More Times a Week (TheBodyPRO)

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