A needle and syringe programme (NSP), syringe-exchange programme (SEP), or needle exchange program (NEP) is a social service that allows injecting drug users (IDUs) to obtain hypodermic needles and associated paraphernalia at little or no cost. It is based on the philosophy of harm reduction that attempts to reduce the risk factors for diseases such as HIV/AIDS and hepatitis. While NSPs provide most or all equipment free of charge, exchange programmes require service users to return used syringes to receive an equal number of new syringes.