There is a high risk of the intravenous drug user falling victim to the disease AIDS (acquired immunodeficiency syndrome). The AIDS virus is transmitted through the sharing of a contaminated needle. A variety of illicit drugs taken by mouth, such as marijuana and cocaine, are known to suppress the user's immune system and could predispose the person to the AIDS infection.
It is estimated that from 10 to 20% of AIDS patients are intravenous drug abusers, although the figure varies from country to country. On average, in industrialized countries in 1991, less than 10% of AIDS was thought to be attributable to bloodborne infection (either by blood transfusion or shared needles).
In the UK, drug use was estimated to be responsible for around 15% of AIDS cases in 1993, falling to around 7% in 1997. In Liverpool and Amsterdam, where injecting drug addicts are able to get clean needles on the state, HIV infection rates were as low as 8%. In Italy, where drug addicts are hounded and imprisoned, infection rates reached 70% in the early 1990s. Also in some areas of Argentina, Brazil, Uruguay and the USA, between 20-50% of injecting drug users were HIV positive.