This report summarizes changes that have occurred in understanding of the health implications of the use and abuse of illegal and legal drugs as a result of research since 1986. It is noted that wherever possible, research findings have been summarized in non-technical language. Some technical material is included because of its basic importance and its relevance to the needs of specialists working on related problems and of those advising lawmakers and other civil authorities on public policy. These chapters are included: (1) "Nature and Extent of Drug Abuse in the United States" which discusses prevalence and consequences of drug use; (2) "Prevention Research" which discusses individual and environmental risk factors; (3) "Treatment Research" which summarizes treatment methods; (4) "Dual Diagnosis: Drug Abuse and Psychiatric Illness" which presents diagnostic issues and treatment strategies for dual disordered patients; (5) "AIDS (Acquired Immunodeficiency Syndrome) and Intravenous Drug Abuse"; (6) "Cocaine and Other Stimulants"; (7) "Marijuana and the Cannabinoids" which discusses health consequences; (8) "Phencyclidine (PCP) and Related Substances"; (9) "Heroin, Other Opiates, and the Immune Function" which focuses on recent research accomplishments; (10) "Sedatives and Anti-Anxiety Drugs"; (11) "Nicotine Dependence"; and (12) "Basic Research on Opioid Peptides and Receptors" which summarizes opioid advances. Bibliographies are included with each chapter. Statistics, tables, and graphs illustrate the report. Author and drug indexes are included. (ABL)