The use or abuse of narcotic drugs is characterized by dependence phenomena. Drug dependence is a psychological and sometimes physical state resulting from the interaction between a living organism and a drug, characterized by behavioral and other responses that always include a compulsion to take the drug on a continuous or periodic basis in order to experience its psychological effects and sometimes to avoid the physical/mental discomfort of its absence.
This definition of drug dependence gives only a broad indication of the nature of the phenomena that are, in large measure, common to the various types or groups of drugs.
The characteristics of drug dependence show significant differences from one type of drug to another, a situation that makes it essential to establish clearly the dependence pattern for each type.
Even though some variations occur between individual drugs in each generic group, the consistency of the pattern of pharmacological actions and responses (human-drug interactions) is sufficiently uniform to permit a delineation of the principal types of dependence. Before describing these types, it should be recalled that not all persons who take dependence-producing drugs become dependent on them. It is wellknown, for example, that most users of alcoholic beverages and cannabis preparations do not become dependent on them.

It is, perhaps, not so widely appreciated that the non-medical use of opium and some drugs with similar effects is not always accompanied by the development of dependence.
The risk of such dependence is, however, much greater with drugs of the opiate (morphine) type than with alcoholic beverages and cannabis preparations. The route of administration is also important; administration into a vein involves not only a greater risk of dependence but also of life-threatening complications.

The following factors are important in the development of drug dependency.
- The frequency and regularity of drug use.
- The characteristics and experience of the user.
- The social acceptability of the drug.
- Community attitudes towards intoxication.