How do I take PEP effectively? PEP must be taken within 72 hours (three days) and to be most effective should be taken within 24 hours. PEP must be taken exactly as instructed by a medical professional and for 28 days. If you skip a dose or fail to complete the full month as this makes it less likely to work Don't double a dose if you miss one If you miss a dose and you remember in less than 24 hours, take the next one as soon as you remember If you miss more than 48 hours of PEP, you should stop taking it. The medication now used for PEP is a single tablet called Truvada and two tablets of raltegravir.