PEP is a combination of HIV drugs which can be used to reduce the likelihood of a HIV negative person getting HIV after they have been exposed to the virus. PEP needs to be prescribed, and can be obtained from A&E departments or sexual health clinics. PEP needs to be taken as soon after exposure as possible to increase its chances of working effectively. In the UK, PEP can be taken up to 72 hours after exposure. However, it is much less likely to be effective when used this late.