The World Health Organization (WHO) prefers to use the term drug dependence to describe psychological and/or physical dependence on licit (painkillers, sedatives) and illicit (drugs: cannabis, amphetamine, heroin...) chemical substances. Regular and continuous intake of these substances leads to addiction and subsequently dependence. This means that the user becomes tolerant to the effects of the substance, and experiences cravings or withdrawal symptoms when not taking it. This addiction causes brain damage and has health consequences, including risks of accident, injury and, in the longer term, liver disease and mental disorders.