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


Orlistat is a drug that works by inhibiting lipase. This prevents the breakdown and absorption of lipids in the GI tract, reducing the overall caloric absorption from food. This mechanism is used to promote weight loss in patients with obesity, in conjunction with dietary changes and exercise regimens. The most common side effects of taking orlistat include steatorrhea, or fatty greasy stools, along with GI upset as a result of fat malabsorption. Reduced fat absorption also impairs intake of fat-soluble vitamins, like vitamin A, D, E, and K. Therefore, patients taking orlistat may also experience fat soluble vitamin deficiencies.

Key Points

  • Orlistat
    • Mechanism
      • Inhibits gastric and pancreatic lipases 
        • Decreases the breakdown and absorption of dietary fat in intestine
    • Clinical use
      • Used for weight loss/obesity management (long-term)
        • Used in conjunction with a healthy diet
    • Adverse Effects
      • Causes diarrhea/steatorrhea
      • Causes a fat-soluble vitamin deficiency
        • Specifically, vitamins A, D, E, and K