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USMLE Guide: Gastrointestinal Medications


This article provides a comprehensive overview of gastrointestinal medications, which are commonly encountered on the United States Medical Licensing Examination (USMLE). Gastrointestinal conditions are prevalent, and understanding the pharmacology of these medications is crucial for medical professionals. This guide aims to assist medical students in preparing for the USMLE by summarizing key information about various gastrointestinal medications.

1. Proton Pump Inhibitors (PPIs)

  • Common examples: omeprazole, esomeprazole, pantoprazole, lansoprazole
  • Mechanism of action: irreversibly inhibit the proton pump in gastric parietal cells, reducing gastric acid secretion
  • Clinical uses: treatment of gastroesophageal reflux disease (GERD), peptic ulcer disease, Zollinger-Ellison syndrome
  • Adverse effects: headache, diarrhea, increased risk of infections (e.g., C. difficile), vitamin B12 deficiency with long-term use

2. H2 Receptor Antagonists

  • Common examples: ranitidine, famotidine, cimetidine
  • Mechanism of action: competitively block histamine h2 receptors on gastric parietal cells, reducing gastric acid secretion
  • Clinical uses: treatment of peptic ulcer disease, GERD, gastritis
  • Adverse effects: headache, dizziness, confusion (rare), increased risk of infections

3. Antacids

  • Common examples: magnesium hydroxide, aluminum hydroxide, calcium carbonate
  • Mechanism of action: neutralize gastric acid, raising gastric pH
  • Clinical uses: symptomatic relief of heartburn, dyspepsia, and acid-related disorders
  • Adverse effects: constipation (aluminum- and calcium-based antacids), diarrhea (magnesium-based antacids), electrolyte imbalances

4. Prokinetic Agents

  • Common examples: metoclopramide, domperidone, erythromycin
  • Mechanism of action: enhance gastrointestinal motility by stimulating smooth muscle contraction or blocking dopamine receptors
  • Clinical uses: gastroesophageal reflux, gastroparesis, postoperative ileus
  • Adverse effects: restlessness, drowsiness, extrapyramidal symptoms (metoclopramide), QT prolongation (erythromycin)

5. Laxatives

  • Common examples: bulk-forming agents (psyllium), osmotic laxatives (polyethylene glycol), stimulant laxatives (senna), stool softeners (docusate sodium)
  • Mechanism of action: promote bowel movements by increasing stool bulk, attracting water to the colon, stimulating peristalsis, or softening stool
  • Clinical uses: constipation, bowel preparation for procedures
  • Adverse effects: abdominal cramps, electrolyte imbalances, dependence (stimulant laxatives)

6. Antiemetics

  • Common examples: ondansetron, metoclopramide, prochlorperazine
  • Mechanism of action: block various receptors involved in nausea and vomiting pathways (e.g., serotonin, dopamine, histamine)
  • Clinical uses: chemotherapy-induced nausea and vomiting, postoperative nausea and vomiting
  • Adverse effects: headache, dizziness, sedation, extrapyramidal symptoms (metoclopramide), QT prolongation (ondansetron)


Mastering the pharmacology of gastrointestinal medications is essential for success on the USMLE. Understanding the mechanisms of action, clinical uses, and adverse effects of these medications allows medical students to make appropriate treatment decisions for patients with gastrointestinal conditions. This guide provides a concise overview of key gastrointestinal medications encountered on the USMLE, aiding in exam preparation and enhancing clinical knowledge.

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