Pre-exposure prophylaxis, also known as PrEP for short, is a medicine that can prevent people from contracting HIV. This medication is taken by people who don’t have human immunodeficiency virus (HIV) but are at high risk for being exposed, or coming into contact with, the virus. 

PrEP blocks the enzymes, or proteins in the blood, that allow HIV to multiply. To block these enzymes, you must build up enough PrEP in your bloodstream. Once PrEP has reached a certain level in your bloodstream, it can prevent HIV from replicating in your body.

Post-exposure prophylaxis, also known as PEP for short, is a medicine that can prevent people from contracting HIV. It can be used in emergency situations by people who don’t already have human immunodeficiency virus (HIV) but may have recently been exposed to HIV. PEP can prevent HIV from spreading through your body after a possible HIV exposure. PEP should be taken within 72 hours of a potential exposure. The sooner you start PEP, the more effective it is at protecting against an HIV infection.