I’ve been at risk of HIV – what can I do? If you’ve been at risk in the last 72 hours, you might be able to prevent HIV infection by taking PEP (Post Exposure Prophylaxis). This is a course of medication designed to prevent you becoming HIV-positive. You need to start PEP ideally within 24 hours of the risk, and no later than 72 hours. The longer you wait, the less chance there is of PEP working. You can get PEP from a sexual health clinic or hospital A&E department. A doctor will advise you if PEP is suitable for you based on the level of risk. For more information about PEP, click here. If you were at risk of HIV more than 72 hours ago, PEP is not suitable but you do need to get tested. You should wait for 4 weeks before going to get a test, as this will make sure the test is accurate. This is because there is a window period between exposure to HIV and when it will show up on a test.