opioids

Definition of opioid
National Cancer Institute

opioid

(OH-pee-OYD)
A substance used to treat moderate to severe pain. Opioids are like opiates, such as morphine and codeine, but are not made from opium. Opioids bind to opioid receptors in the central nervous system. Opioids used to be called narcotics. An opioid is a type of alkaloid.

Source: NCI Dictionary of Cancer Terms