This document discusses psychoactive substances and substance use disorders. It begins with basic definitions of psychoactive substances and reinforcers. It then categorizes common drugs like depressants, stimulants, opioids, hallucinogens, and inhalants. It describes DSM-IV substance use disorders and induced disorders. It provides more detailed definitions and symptoms of substance abuse and dependence. It also discusses concepts of tolerance, addiction, and worldwide alcohol consumption. Finally, it outlines various neurological and psychiatric disorders caused by substance use and approaches to treatment.