According to definition of the World Health Organization 1964 "drug dependence", a condition of mental or mental and physical dependence on a legal or illegal drug with central nervous effect, which is characterized by the periodic or constantly repeated consumption of this substance and whose characteristics vary depending upon kind of the taken drug. This definition is roughly equivalent to the dependence syndrome of ICD-10: "Dependence is defined as a cluster of cognitive, behavioural and physiological symptoms that indicate a person has impaired control of psychoactive substance use and continues use of the substance despite adverse consequences."
The WHO differentiates between:
A further characteristic of physical dependence exists in the so-called tolerance increase, i.e. ever higher doses of the drug must be taken, in order to achieve the same effect. "Psychological or psychic dependence refers to the experience of impaired control over drinking or drug use (see craving, compulsion), while physiological or physical dependence refers to tolerance and withdrawal symptoms."
The term can be also used with specific reference to a particular drug or class of drugs: Amphetamine dependence, Barbiturate- alcohol dependence, Cannabis dependence, cocaine dependence, hallucinogen dependence, opioid dependence; to the causes and developing conditions of a dependence.