Opioid

An opioid is a drug that can suppress the perception of pain and calm a person's emotional response to pain by reducing the effect of pain signals sent by the nervous system. Opioids (also called opiates or narcotics) produce a feeling of well-being (euphoria) and cause mood changes, cloudy thinking, and deep sleep.

Side effects of opioids may include constipation and nausea. Frequent use of opioids may make a person dependent on them.

Commonly prescribed legal opioids include codeine and morphine. Heroin is an example of an illegal opioid.