Pre-exposure prophylaxis

Pre-exposure prophylaxis (PrEP) is the long-term use of a prophylactic treatment for a disease prior to exposure to the cause of that disease, so that the prophylactic treatment will already be in place when exposure occurs, and may either be able to prevent the disease from being contracted, or at least ensure that the resulting disease is treated from its outset, whether or not the patient is aware that infection has occurred.

The most common use of this term is to refer to the controversial use of antiretroviral treatments by people at high risk to exposure to HIV, in an attempt to either prevent HIV infection from taking hold, or at least to postpone or prevent the development of AIDS subsequent to HIV infection.

The effectiveness of PrEP for HIV is as yet unproven, and medical trials of PrEP have collapsed due to protests about the exposure of members of the control group to HIV. One criticism of PrEP for HIV is that it might encourage risky behavior such as barebacking, possibly increasing, rather than decreasing, the risk of HIV infection both to the individual and the population at large.

Pre-exposure prophylaxis can also refer to the aggressive use of vaccination, for example in an attempt to prevent rabies in people such as laboratory workers who are high risk for being bitten by rabid animals.