What are the contraindications of going onto PrEP? The number contraindication to go onto PrEP is that the person is already infected with HIV. For this reason, it’s very important at the beginning of the screening process that we do a test for HIV. We’re looking for HIV-1 antibodies, HIV-2 antibodies, and if we can use a fourth generation that checks for p24, this greatly reduces the window period. If somebody has had a potentially high risk exposure to HIV a month before they’re considering starting PrEP, it’s worthwhile to carefully monitor their status to make sure that the person has not had an exposure and infection with HIV beforehand. If the potential risk and exposure to HIV is within 72 hours, it’s worthwhile talking with this patient about going PEP or post-exposure prophylaxis.