State laws, syringe exchange, and HIV among persons who inject drugs in the United States: History and effectiveness.

In 1981, when acquired immune deficiency syndrome (AIDS) was first observed among persons who inject drugs, almost all US states had laws criminalizing the possession and distribution of needles and syringes for injecting illicit drugs. We reviewed changes to these laws to permit 'syringe exchanges' and the provision of public funding for such programs. Most of the changes in law occurred during the 1990s, 5-10 years later than in many other countries.