PEP, or post-exposure prophylaxis, is a combination of medications that an HIV-negative person takes for 28 days AFTER a possible exposure to HIV if they weren't taking PrEP or missed taking PrEP as prescribed. PEP is more effective the sooner it’s started, and must be started within 72 hours of the exposure.
You may benefit from PEP if, within the past 72 hours, you have been exposed to the pre-semen (pre-cum), semen (cum), vaginal fluid, rectal fluid, or blood from someone with an unknown HIV status, or someone who has HIV and you don't know if they are "undetectable".
A doctor or other clinician must prescribe PEP. During regular office hours, ask your doctor or go to a sexual health clinic. During off hours, go to an urgent care or emergency room. Many pharmacies can fill the prescription, but consider a backup pharmacy just in case.
For more information, download: PEP info sheet.