Of the 230 million people in America who use illicit substances, 27 million have high-risk substance abuse problems.
 The exact cause of substance abuse is not clear, but there are two predominant theories: either a genetic predisposition or a habit learned from others, which, if addiction develops, manifests itself as a chronic debilitating disease
 For example, the consumption of seven illicit drugs (amphetamines, cannabis, cocaine, ecstasy, legal highs, LSD, and magic mushrooms) is correlated and the Pearson correlation coefficient r>0

