A narcotic (also called opioid or opiate) is a substance that can suppress perception of pain and calm the emotional response to pain by reducing the number of pain signals sent by the nervous system. Narcotics produce a feeling of well-being (euphoria) and cause mood changes, cloudy thinking, and deep sleep.

Commonly prescribed legal narcotics include butorphanol, codeine, hydrocodone, meperidine, and morphine. Heroin is an illegal narcotic. Side effects of narcotics may include constipation and nausea. Frequent use of narcotics may make a person dependent on them.