 In many countries users are supplied equipment free of charge, others require payment or an exchange of dirty needles for clean ones, hence the name.A 2010 review found insufficient evidence that NSP prevents transmission of the hepatitis C virus, tentative evidence that it prevents transmission of HIV and sufficient evidence that it reduces self-reported injecting risk behaviour.It has been shown in the many evaluations of needle-exchange programmes that in areas where clean syringes are more available, illegal drug use is no higher than in other areas.