Approximately 100 years after cocaine entered into use, a new variation of the substance emerged. This substance, crack, became enormously popular in the mid-1980s due in part to its almost immediate high and the fact that it is inexpensive to produce and buy. Crack is a highly addictive form of cocaine that is typically smoked. The term "crack" refers to the crackling sound heard when the substance is heated, presumably from the sodium bicarbonate that is used in the production of crack. In the U.S.A the Harrison Narcotics Tax Act was passed in 1914 to control the sale and distribution of heroin and other opiates. The law did allow heroin to be prescribed and sold for medical purposes. In particular, recreational users could often still be legally supplied with heroin and use it. In 1924, the United States Congress passed additional legislation banning the sale, importation or manufacture of heroin in the United States. It is now a Schedule I substance, and is thus illegal in the United States. Although the root causes of drug addiction remain unclear, the new study reveals that scientists have identified a number of biological, psychological and social conditions that can help to identify whether a person will become an addict. | 
