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 92%-99% reduction in HIV risk. How effective PrEP is depends on a few things, like how often you take it. If a daily dose is missed, the level of HIV 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]

Women and Trans people

Daily dosing of PrEP is much more important for cisgender women, and trans folks. There are a number of reasons for this linked with both hormones and the different body tissues in the rectum, vagina, neo-vagina, or front-hole. Suffice to say, if you’re a women or person of trans experience – PrEP works – it’s just more important to take your pill every day.

It only works if you take it. People who use PrEP correctly and consistently have higher levels of protection against HIV.

So just how effective is PrEP?* [1]

·         For people who take 7 PrEP pills per week, their estimated level of protection is 99%.

·         For people who take 4 PrEP pills per week, their estimated level of protection is 96%.

·         For people who take 2 PrEP pills per week, their estimated level of protection is 76%.

This means that taking daily PrEP is going to give you the best constant protection against HIV.


 When am I protected?

When starting PrEP, it takes at least seven days of taking your PrEP every day to reach high levels of protection against HIV. It takes a while for PrEP to be absorbed fully and to build up to maximum potency in your body. 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 four weeks after the last significant exposure. If you have another potential exposure in that time, simply extend the period of time you are ‘stopping’ PrEP. If you had a potential exposure on the 7th day where you were in your month ‘cool down’ period, simply extend that cool down period for another week until you have 28 risk free days.

*for cisgender men who have sex with men


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[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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