Needle sharing is the practice of intravenous drug-users by which a syringe is shared by multiple individuals to administer intravenous drugs, and is a primary vector for diseases which can be transmitted through blood (blood-borne pathogens).
Needle-exchange programmes (NEP), a form of harm reduction policy, provide new needles to persons addicted to drugs in exchange for used ones in order to help control the spread of disease. In the United States, there are three distinct prohibitions on needle exchange programs at the federal level — the Ryan White CARE Act, the Substance Abuse and Mental Health Services Administration (SAMHSA) authorization, and the 1997 Labor-Health and Human Services (HHS) Education appropriations legislation. However, many states still provide the service despite the federal legislation, especially in large cities where intravenous drug use is a major health concern. A study in New York State found that during the course of 12 months NEP prevented a roughly calculated 87 infections of HIV by preventing needle sharing. Also, NEP have decreased the spread of HIV by one third to two fifths.
Someone who has been injected with a medicine or drug using a syringe or needle that has been used by someone with HIV may be at risk of getting HIV as well. However, because a person may not know whether someone has HIV or not, as a precaution, an individual should never reuse a needle or syringe. An individual may never know whether someone else or himself has a terminal or severe infection that is contagious. Therefore, it is never safe to share a needle or syringe with another individual. 
- Helpern, Milton (1977). "An Epidemic of Sorts". Autopsy : the memoirs of Milton Helpern, the world's greatest medical detective. New York: St. Martin's Press. pp. 70–71. ISBN 0-312-06211-7.
- Clemons, Thomas. "Needle Exchange Program".
- "Needle Exchange Programs Promote Public Safety".
- "Sharing Needles", BBC
- Needle Exchange Program FAQ
- Helpern, M (March 30, 1934). "Malaria among drug addicts in New York City - An epidemic of estivo-autumnal and quartan malaria among drug addicts in New York City transmitted by contaminated hypodermic syringes". Public Health Rep. 49 (13): 421. doi:10.2307/4581127. Reprinted as Helpern M (1976). "Malaria among drug addicts in New York City (March 30, 1934): An epidemic of aestivo-autumnal and quartan malaria among drug addicts in New York City transmitted by the use of contaminated hypodermic syringes". Public Health Rep. 91: 477–479. PMC . PMID 19313398.