This document reviews various definitions of the nature and classification of drugs. Difficulties with existing categorizations which use such bases as clinical utility, molecular structure, effects on the central nervous system, legality, and hazard potential are disucssed. A more meaningful categorization based on the availability and sources of psychoactive drugs is offered. Categories include herbal, over the counter, prescription, unrecognized, tabacco, alcohol, and illicit drugs. Connotative meanings of the drug categories are examined in terms of the semantic differential. College student interests concerning drug categories are reported. Concerns about psychoactive drugs are mentioned. A typology of use patterns associated with motivations includes experimental, social-recreational, circumstantial-situational, intensified, and compulsive drug use. Use patterns are summarized. A traditional evaluation of use patterns reviews drug use, misuse, and abuse definitions. Finally addiction, habituation, and drug dependence are discussed. (Author/JLL)