dependence

the physical and/or psychological effects produced by the habitual taking of certain drugs, characterized by a compulsion to continue taking the drug. In physical dependence withdrawal of the drug causes specific symptoms (withdrawal symptoms), such as sweating, vomiting, or tremors, that are reversed by further doses. Substances that may induce physical dependence include alcohol and the 'hard' drugs morphine, heroin, and cocaine. Dependence on 'hard' drugs carries a high mortality, partly because overdosage may be fatal and partly because their casual injection intravenously may lead to infections such as HEPATITIS and AIDS . Treatment is difficult and requires specialist skills. Much more common is psychological dependence, in which repeated use of a drug induces reliance on it for a state of well-being and contentment, but there are no physical withdrawal symptoms if use of the drug is stopped. Substances that may induce psychological dependence include nicotine in tobacco, cannabis, and many 'soft' drugs, such as barbiturates and amphetamines.