Stopping PrEP - 28 day recommendation?


Hi Damon - thanks for your hard work in managing this forum. I have a question about what the doctors you know are telling their patients about stopping PrEP.

On the one hand, most organizations / sources recommend staying on PrEP for 28 days after the most recent exposure before stopping PrEP. On the other hand, the IPERGAY / "on-demand" study suggests that 2 days/pills after (assuming 2 pills before sex) is sufficient.

There is obviously a huge discrepancy between 2 days and 28 days before stopping PrEP, and while I want to make sure I've continued long enough to be "covered", I also don't want to take more pills than I have to in a period where I'm not sexually active.

I have also heard some doctors splitting the difference and advising to continue PrEP 7 days after the last exposure. So for people taking daily PrEP (like me) what do you hear doctors currently telling patients on how long to continue? Thanks much.


Hi there- thank you for your kind words!

So as with most things PrEP there are political and geographical differences in the types of information you'll read. Dr. Robert Grant was the Principal Investigator of Iprex, and maintains awareness and communication about PrEP protocols around the world. So when I'm not sure about what's being said, or what the correct answers are, I look to him.

Back in early 2015, the data came out that showed on-demand dosing (through "Ipergay") clearly prevented new HIV transmissions for anal sex. That research was just validated in July through the results of the Prevenir study, where over 1600 participants who followed the on-demand PrEP strategy had 100% protection ( Not one participant in Ipergay, nor Prevenir, acquired HIV when they followed the regimen.

As you pointed out, this regimen only requires two consistent doses of PrEP after the last potential exposure to detectable levels of HIV via anal sex. So if I were to go out and get filled with cum on a Saturday night, Ipergay would instruct me to take a dose of Truvada (or its generic equivalent) on Sunday night 24 hours after the last cumload, and then again on Monday night another 24 hours after that. No further doses would be necessary for maximal protection.

Based on this data, Dr. Grant has told us, "[28 days] may be more than what's needed. Two doses after a potential exposure to HIV appears to provide substantial protection in the Ipergay study if men were taking PrEP before the exposure." []

Unfortunately, the U.S. CDC has yet to acknowledge this data, and still suggests the 28 day guidelines. But there is no research to support nor sustain this view, and the updated data from Ipergay and Prevenir suggests that these two subsequent doses are sufficient.

When in doubt, you certainly have the right to adjust your own practices to the available data. For some that might be taking PrEP for a week after a potential HIV exposure. For some it might be three or four days. The most important thing is that you make sexual decisions that are based in data, information, and pleasure.

Please remember as well that when we are talking about on-demand regimens we are only talking about anal sex and that the research has only included cisgender men. We still have no data to tell us if on-demand dosing would work for vaginal or front-hole sex.

To learn more about PrEP and the different regimens being used by consumers around the world, please feel free to join us in the Facebook PrEP Facts group:

Thank you again for writing in!