Prep HIV stands for pre-exposure prophylaxis, which is a medicine taken to prevent getting HIV from sex or injection drug use. PrEP is highly effective for preventing HIV when taken as prescribed. It reduces the risk of getting HIV from sex by about 99% when taken as prescribed. Among people who inject drugs, it reduces the risk by at least 74% when taken as prescribed. PrEP is much less effective when it isnt taken consistently. PrEP is only available by prescription. It is important to note that PrEP protects against HIV but not against other sexually transmitted infections (STIs) or other types of infections. Combining PrEP with condoms will reduce the risk of getting other STIs.