PEP is an antiretroviral treatment that is used to prevent a person from contracting HIV after having possibly been exposed to the virus.
PEP is however not effective in all instances. It must be taken within 72 hours after having contracted the virus and can have better results if taken before 48 hours have passed after possible contraction of the virus.
It is very important to ask for the PEP as soon as possible but within 72 hours of the sexual assault or rape.