Definition: Pre-exposure prophylaxis is the method of taking one or more types of HIV medication prior to having sex in order to limit the risk of HIV transmission. There has long been some suggestion that PreP might work from studies involving monkeys, but for years there were doubts about its efficacy in humans. However, those doubts have been resolved -- if not ongoing concerns about its potential risks.
In May 2012, the FDA approved the single-tablet combination medication Truvada for use in people at high risk for HIV transmission through sexual contact. However, although PreP can be effective when used properly, it should not be seen as a substitute for condoms, when they are a reasonable option.
Sources:
Okwundu CI, Okoromah CA. (2009) "Antiretroviral pre-exposure prophylaxis (PrEP) for preventing HIV in high-risk individuals." Cochrane Database Syst Rev.(1):CD007189.
