This document provides an overview of drug abuse and addiction. It defines key terms like drugs, controlled substances, drug abuse, and reasons for abuse. It describes common signs of abuse and polydrug abuse. It also covers warning signs, routes of administration, and how drugs affect the brain. The document classifies common drugs and explains concepts like tolerance, dependence, addiction, treatment, withdrawal symptoms, and effects of addiction. It provides details on major drug classes like opioids, depressants, stimulants, hallucinogens, and anabolic steroids.