How long do I have to take PrEP before it is highly effective? PrEP reaches maximum protection from HIV for receptive anal sex (bottoming) at about 7 days of daily use. For receptive vaginal sex and injection drug use, PrEP reaches maximum protection at about 21 days of daily use.

How long after starting PrEP is it effective?

For people who have anal sex, PrEP becomes highly effective after seven days if it is taken every day. It takes longer to become effective—21 days of daily use—to be effective at preventing HIV after injection of drugs or in people having vaginal sex.

Can I take PrEP after 2 days?

If you are continuing to have sex, take 1 pill 24 hours after the double dose and continue taking 1 pill every 24 hours for the days you are having sex. Continue taking PrEP until you have taken 2 doses after your last sex. This means taking 1 dose on each of the 2 days after your last sex.