Prep on demand not taken correctly


Hi Damon Jacobs,so the thing is I done on demand prep, the problem is that I got it wrong. Instead of taking double pill one day + 1 pill 24h later + another pill another 24h. i took 2 pills on thursday, did not took on Friday, took from Saturday forward every day. the risky behaviour ( receptive anal ) was on Sunday. do you think i can have the risk of not being completely protected ? i would appreciate an answer. thank you.


Hi there,

Okay, so first thing to acknowledge here is that although you did not completely follow the timeline of the on-demand dosing regimen, you came pretty close. You didn't say exactly what time of day or night you took the doses, as the spacing of those times could have an impact here on your advocacy. For instance, how much time was allotted between the 2 Thursday doses and the resuming single dose on Saturday? Was it 48 hours, 26 hours, this is unclear.

The other thing I'm not clear on is what time you had anal sex on Sunday? Were the Saturday and Sunday doses taken within 24 hours of the Sunday event?

You don't mention if you followed the on-demand protocol after having sex. Did you follow the regimen by taking a single dose on Monday after having sex on Sunday, and then another single dose on Tuesday?

And finally, you don't mention anything about your partner's status. True, that is not the central issue here, and I agree that we are each 100% responsible for our own HIV status. But when figuring out possibilities and calculations, it helps to take his information into account. Is he HIV negative on PrEP? If so, his risk of having HIV are nearly zero. Is he HIV positive with an undetectable viral load? If so he is not capable of transmitting HIV to others.

There are a lot of "what-if / then" questions here to consider in your question especially pertaining to the timeline. And even if we had all the answers, I'd still have to tell you there is no conclusive science then can satisfactorily answer your questions. The science tells us that following the On-Demand protocol for anal sex bring the risk of HIV acquisition to nearly zero ( If you take it outside the studied dosing schedule, the protection varies, but by how much it varies we simply don't know.

I am personally very grateful that the on-demand dosing schedule exists, and that is a medically proven option. But to be honest with you, for me personally, that is way too confusing for me to follow consistently. As a consumer of PrEP I prefer the daily regimen, as it allows for variability in my schedule, time changes when I travel, even an occasional skipped dose here or there, none of which affect PrEP's efficacy.

But for others the on-demand regimen is a better option in terms of time, money, and sexual frequency. Again, that is best for people who can follow a structured regimen closely. Some other viable options for taking PrEP are listed by the "I Want PrEP" folks in the U.K. here:

So we're going to leave here where we started: You may not have adhered perfectly to the structured schedule, but it seems you came awfully close, and that there was some protection offered to you by the way you took the drug. But how much protection was there, and how much you were truly put it at risk, can not be determined with the information given. That may not be a satisfactory answer, but I do hope it encourages you to to use a regimen that has science behind it, and can help you feel secure and empowered by your decisions.