This document discusses substance abuse. It defines substance abuse as persistent or sporadic drug use inconsistent with or unrelated to acceptable medical practice according to the WHO. June 26th is recognized as International Day Against Drug Abuse and Illicit Trafficking. The document provides statistics on substance abuse worldwide and in India, noting that around 190 million people abuse drugs globally and an estimated 1 million heroin addicts are registered in India. Common substances abused in India include tobacco, alcohol, cannabis, and opiates. Substance abuse causes immense human distress and crime. The document classifies substance use disorders and discusses some of the biological and psychological causes of substance abuse.