This document discusses substance use, abuse, and addiction. It defines substance use and abuse, describes how substances affect the brain's reward system, and lists some common classes of substances like depressants, stimulants, and opioids. The document also examines some causes of substance abuse, signs and symptoms, and health risks. Finally, it discusses the stigma associated with substance abuse and how labels can negatively impact people's self-concept and willingness to seek help. Reducing stigma is important so people feel comfortable accessing treatment and support services.