Medicine & USMLE

Bulk Forming Laxatives (Psyllium, Methylcellulose)

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


Bulk forming laxatives, including psyllium and methylcellulose, work as indigestible fiber supplements to increase the absorption of water into the stool. This can soften the fecal mass to treat constipation and improve bowel movements. Remember that bulk-forming laxatives must be taken with a full glass of water for appropriate function.

Key Points

  • Bulk-Forming Fiber Laxatives
    • Key Drugs
      • Psyllium (Metamucil)
      • Methylcellulose (Citrucel)
    • Mechanism
      • Works as a non-absorbable dietary fiber; increases fecal bulk by absorbing water to soften fecal mass
    • Clinical Use
      • Constipation
        • Take with plenty of water
        • May take several days before desired effects are seen
      • May treat mild diarrhea in patients with diverticulosis and irritable bowel syndrome (IBS)
    • Side Effects and Adverse Reactions
      • Abdominal cramping