Opioids

Ligand

mu receptor

kappa receptor

delta receptor

Morphine 

Agonist (strong)

Agonist (weak)

Agonist (weak)

Naloxone

Antagonists (strong)

Antagonist (medium)

Antagonists (weak)

Naltrexone 

Antagonist (strong)

Antagonist (strong)

Antagonist (weak)



NOTE: Naloxone is a competitive antagonist at mu-opioid receptors, which are the primary sites of action for opioid analgesics. By blocking these receptors, naloxone can reverse the effects of opioid overdose.



Reference: 

1. Essentials of Medical Pharmacology, KD Tripathi, 8th edition, P. No. 508 

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