Q and A


Have I done on-demand PrEP right?

So I have a question. Not sure if on-demand PrEP works like this.

Thursday: Took 2 pills at 4pm (didn’t have sex as expected).
Friday: Took 1 pill at 4pm. Had sex at 2AM
Saturday: Took 1 pill at 630pm. Had sex at 9pm.
Sunday: Took 1 pill at 3pm.
Monday: Took 1 pill at 3pm

Did on-demand prep work with this regimen. This is my 1st time doing it.


Hi, how are you doing?

Yes. This is how on-demand PrEP works.

As long as you had the double dose 2-24 hours before your first sexual encounter and 2 single doses after your last, PrEP will work. This is what you did.

As you kept your PrEP at a similar time each day throughout, PrEP will have worked.



  1. Josh Peasegood

    Hi Ace, yes it is better practise to do this. As an example, take the initial double dose at 14:00 on Monday, sex later on at 22:00 on the same day. Then on Tuesday and Wednesday take the single dose at 14:00 each day. The time of sex should not effect the time you take PrEP.

  2. Ace

    Hi Josh,

    Thanks :) But would you say going forward, its better practice to take the followup doses 24 and 48 hours after the first dose? Ace.

  3. Josh Peasegood

    Hi Ace, this is not likely to be a problem. As the initial dose is a double dose, there is a higher concentration of PrEP in your body than would be fro a single pill. This will allow for you being late in your following doses. Being 12 hours late is going to be covered by this initial double dose.

  4. Ace

    Hi Josh,

    I’ve got a similar question. I may have not taken the on-demand PrEP exactly as I should’ve.

    I took the two pills within the timeframe of 2-24 before engaging, but the two doses came 24 and 48 hours after I’d finished engaging, rather than 24 and 48 hours after the first two pills. I think I’d misread the instructions. So because of the timings, the follow-up single tablets may have been likely up to around 12 hours too late. Have I not done it properly?



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