Classification

• Full agonists
  • Morphine, heroin
  • Methadone
  • Meperidine
  • Codeine
  • Fentanyl
• Partial agonist: buprenorphine
• Mixed agonist/antagonists
  • Butorphanol
  • Nalbuphine
  • Pentazocine
• Full antagonists
  • Naloxone
  • Naltrexone
  • Methylnaltrexone

Adverse effects

• Constipation (not affected by tolerance, most common and persistent opioid side effect.)