Post-exposure prophylaxis (PEP) is medicine to help prevent HIV infection after possible contact. It's for emergency use if you had unprotected sex or were stuck by a used needle. PEP is a combination of medicines taken every day for 28 days. It helps to reduce the chances of the HIV virus taking hold in your body.
You need to start PEP quickly after contact with HIV. It works best within 72 hours (3 days) after contact. It's best to take it as soon as possible. PEP is not a guarantee. But it greatly lowers the risk of HIV infection if started within 72 hours of possible exposure to HIV. If you may have had contact with HIV, call your doctor right away. Or you can go to your local health clinic or urgent care.