Medicine & USMLE

Antidiarrheals (Loperamide, Diphenoxylate-Atropine)

GI Drugs
  1. Ondansetron
  2. Sucralfate
  3. Docusate (Stool Softener)
  4. Bulk Forming Laxatives (Psyllium, Methylcellulose)
  5. Osmotic Laxatives (Lactulose, PEG)
  6. Stimulant Laxatives (Senna, Bisacodyl)
  7. Antidiarrheals (Loperamide, Diphenoxylate-Atropine)
  8. Bismuth Subsalicylate
  9. Antacids
  10. Proton Pump Inhibitors (PPIs)
  11. H2 Blockers
  12. Metoclopramide
  13. Misoprostol
  14. Orlistat
  15. Octreotide


Antidiarrheals, including the drugs loperamide and diphenoxylate-atropine, are used to reduce frequency and liquidity of stool.

Key Points

  • Antidiarrheals
    • Key Drugs
      • Loperamide (Imodium)
        • Synthetic analog of the opioid meperidine
      • Diphenoxylate-atropine (Lomotil)
        • An opiate combination drug with anticholinergic properties
    • Mechanism
      • Slows intestinal motility by binding to the opiate receptor in the wall of the GI tract
      • Increased absorption of fluids and electrolytes in the intestinal tract
    • Clinical Use
      • Treats Diarrhea
        • Provide symptomatic relief (decrease in frequency and liquidity of stool)
        • Does not treat the underlying cause (e.g. bacterial infection would also need antibiotics)
    • Side Effects and Adverse Reactions
      • Central Nervous System Effects (Diphenoxylate)
        • If given in high doses; generally not seen when given in a low dose
        • Euphoria, CNS depression, dizziness, fatigue
        • The atropine addition in diphenoxylate-atropine discourages abuse because patients will receive anticholinergic side effects in addition to opioid side effects