Classification of Opioid Drugs

Opioid drugs can be classified in a number of ways but, from the medical point of view, the most obvious, simple, and useful classification is on the basis of their clinical importance. To this 

Opioid drugs show a wide range of agonist and antagonist effects. For example, morphine is an agonist but in relative terms, phenazocine is 

Drug Origin Chemical class Analgesic potency Main receptor(s) recognized Function at receptor  

Morphine Naturally occurring Phenanthrene Intermediate-strong P Agonist 

Codeine Naturally occurring Phenanthrene Weak-4ntennediate p,8 Weak agonist 

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