This document discusses opioids and their medical uses and effects. It begins by defining opioids as substances that act on opioid receptors to produce morphine-like effects. It then discusses the classification of opioids, including natural, semi-synthetic, fully synthetic, and endogenous opioids. The document outlines several major opioids - morphine, codeine, heroin, and methadone - and describes their histories, mechanisms of action, medical uses, and side effects. It also discusses opioid antagonists that are used to treat overdose and the detection of various opioids. In conclusion, the document notes the regulated global supply of opioids to balance pain treatment with abuse and addiction.