PrEP is a prevention method used by people who are HIV-negative and at high risk for being exposed to HIV through sexual contact or injection drug use. When someone is exposed to HIV through sex or injection drug use, these medicines can work to keep the virus from establishing an infection.
PEP refers to the use of antiretroviral drugs for people who are HIV-negative after a single high-risk exposure to stop HIV infection. PEP must be started as soon as possible to be effective – always within 72 hours of a possible exposure – and continued for 4 weeks.