Estimates in this report are based on the combined 1991-93 National Household Survey on Drug Abuse (NHSDA), a database of approximately 90,000 respondent records. The estimates are weighted to represent the civilian, noninstitutionalized population of the United States. Analyses are reported separately for the following categories: Alcohol (any use and regular use); Cigarettes (any use and regular use); Marijuana, Cocaine, Hallucinogens, Inhalants, Heroin (ever used); and Stimulants, Analgesics, Tranquilizers, Sedatives (ever used nonmedically). The report also discusses the measurement of the incidence of drug use; reviews the NHSDA questionnaire instruments; defines the statistical measures of incidence that are used in the report; discusses the sociodemographic control variables used; and explains the methods of sample weighting, statistical testing, and the rules for suppression of estimates that are insufficiently precise. Notes, figures, tables, appendix, references