ABSTRACT
Definitions A clear understanding of some definitions is important in opioid pharmacology. An opioid is any drug acting at the opioid receptor. An opiate is a naturally occurring opioid derived from opium (from the Greek opion, poppy juice), e.g. morphine, codeine, papaverine. The term narcotic is derived from the Greek narco (to be numb) and is used often in a legal sense to describe a drug of addiction.
