Q and A


Will taking PrEP late work with on demand dosing?

Hi, I take PrEP with on demand dosing and after having sex after my first double dose i remembered my first dose post sex on time. However, my second dose was 5h late and 3rd dose was 5h late too. Will this affect my level of protection and should i continue taking it 5h late every day?



Thanks for your question. The easy answer is that you will probably be fine.

Both the drugs in PrEP stay in your body to allow for a few hours being late with dosing.

It is better to try to take them at the right time.

The after sex doses with on demand dosing only need to be taken 24 hours and 48 hours after the first double dose. Taking an extra dose for a third day will not do any harm though.

If you are still having sex every day though, then continue taking PrEP until 24 and 48 hours after the last time you had sex.

More information on real life examples for on demand dosing.


  1. Josh Peasegood

    Hi Worried, as the first dose is a double dose and you took the second on time, being late with the third dose is unlikely to reduce how effective PrEP will be. Being 8 hours late with the last dose can mean that the on-demand PrEP will not be as effective, but taking the initial double dose on time still means this is a low risk exposure. You do not need to be worried.

  2. Worried

    Hey. So I take prep on-demand and took my first 2 tablets dose Sunday around 4pm. (That was 2,5hours before sex). Monday I took 1 tablet around 4pm also. Tuesday I forgot to take the pill at the same time and took it 8 hours late. Should I be worried?

  3. Josh Peasegood

    Hi Sam, yes this can still be effective. While it is recommended to start PrEP 2-24 hours before sex, even an hour before is still going to provide some protection.

  4. Sam


    Using condom of my partner is not satisfying for him, so he is removed the latex condom and do it analy. That specific hour I just took the Prep, no 2 to 24hrs before the activity. CAN THAT STILL BE EFFECTIVE. NEED YOUR RESPONSE ASAP please. Thank you.

  5. Josh Peasegood

    Hi Daniel, this is okay. You do not need to be worried. Being half an hour late/early of the time the day before is not going to reduce how PrEP works. As your partner was also on PrEP this is a very low risk encounter regardless of you even being on PrEP.

  6. Daniel

    So, for the first time I was on prep on demand.
    Took on Friday about 3hours before sex(2pills) at 12pm
    Then Saturday, took it at about 12:30pm, 30minutes or so later.
    Then on Sunday I took it at 11:30am, 30minutes or so earlier.
    Then Monday I took it at 12pm.

    We had bare sex and finished inside.
    He was saying that he’s on prep too.

    Do you think it will be okay or should I be worried?


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