Receptor |
Morphine |
Naloxone |
Naltrexone |
mu |
Agonist (strong) |
Antagonists (strong) |
Antagonists (strong) |
kappa |
Agonist (weak) |
Antagonists (medium) |
Antagonists (strong) |
delta |
Agonist (weak) |
Antagonists (weak) |
Antagonists (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.