Medicine & USMLE


Gastrointestinal Pharm
  1. H2 Blockers (Cimetidine, Ranitidine, Famotidine)
  2. Proton Pump Inhibitors (PPIs)
  3. Misoprostol
  4. Orlistat
  5. Antacids
  6. Bismuth & Sucralfate
  7. Octreotide
  8. Diphenoxylate vs. Loperamide
  9. Ondansetron
  10. Metoclopramide
  11. Bulk-forming Laxatives
  12. Senna
  13. Docusate
  14. Aprepitant


Senna is a laxative that works by irritating the bowel to stimulate bowel movement. As a laxative, it treats constipation but too much laxative can cause diarrhea. A benign but high-yield side effect is melanosis coli, which describes a black-brown discoloration of the colon.

Key Points

  • Senna
    • Mechanism
      • Stimulant laxative
        • Enteric nerve stimulation → colonic contraction
        • Works by irritating sensory nerve endings, which stimulates colonic motility and reduces colonic absorption
    • Clinical Use
      • Laxative for constipation
    • Adverse Effects
      • Diarrhea
      • Melanosis Coli
        • Harmless black coloration of colon, that may be observed on colonoscopy