Introduction to the gastrointestinal system and medications

The gastrointestinal (GI), or digestive, system breaks down food, absorbs nutrients, and removes waste from the body.

Common GI disorders include gastroesophageal reflux disease (GERD), peptic ulcers, diarrhea, constipation, hepatitis, and inflammatory bowel disease.

Medications used to treat GI disorders are among the most commonly prescribed drugs. Examples include antacids, proton pump inhibitors, and laxatives.

Table showing common drug classes and examples of the gastrointestinal system

Drug class	Generic name	Brand name(s)	Primary use
Antacids	Aluminium hydroxide, magnesium hydroxide, calcium carbonate	Amphojel, Milk of Magnesia, Tums, Rolaids	Neutralize gastric acidity
Proton pump inhibitors	Omeprazole, pantoprazole, esomeprazole	Prilosec, Protonix, Nexium	Decrease the production of gastric acid, peptic ulcers, and gastroesophageal reflux disease (GERD)
Histamine (H2) blockers	Famotidine, cimetidine	Pepcid, Tagamet	Decrease the production of gastric acid, peptic ulcers, and gastroesophageal reflux disease (GERD)
Antidiarrheals	Loperamide, Bismuth subsalicylate	Imodium A-D, Lomotil, Pepto-Bismol	Treatment of diarrhea
Laxatives	Polyethylene glycol, docusate, psyllium, bisacodyl	MiraLAX, Colace, Metamucil, Dulcolax	Treatment of constipation

Note: Ranitidine (Zantac) was once a commonly cited H2 blocker, but the FDA requested its withdrawal from the US market in April 2020 due to contamination with NDMA, a probable carcinogen. The product now sold as “Zantac 360” contains famotidine, not ranitidine.

Gastrointestinal (GI) System Overview

Function: breaks down food, absorbs nutrients, removes waste
Common disorders: GERD, peptic ulcers, diarrhea, constipation, hepatitis, inflammatory bowel disease
GI medications (antacids, proton pump inhibitors, laxatives) are among most commonly prescribed drugs

Antacids

Examples: aluminum hydroxide, magnesium hydroxide, calcium carbonate
Brands: Amphojel, Milk of Magnesia, Tums, Rolaids
Use: neutralize gastric acidity

Proton Pump Inhibitors (PPIs)

Examples: omeprazole, pantoprazole, esomeprazole
Brands: Prilosec, Protonix, Nexium
Use: decrease gastric acid production; treat peptic ulcers and GERD

Histamine (H2) Blockers

Examples: famotidine, cimetidine
Brands: Pepcid, Tagamet
Use: decrease gastric acid production; treat peptic ulcers and GERD
Note: ranitidine (Zantac) withdrawn by FDA (April 2020) due to NDMA contamination (probable carcinogen)
- “Zantac 360” now contains famotidine, not ranitidine

Antidiarrheals

Examples: loperamide, bismuth subsalicylate
Brands: Imodium A-D, Lomotil, Pepto-Bismol
Use: treatment of diarrhea

Laxatives

Examples: polyethylene glycol, docusate, psyllium, bisacodyl
Brands: MiraLAX, Colace, Metamucil, Dulcolax
Use: treatment of constipation