Gastrointestinal Drug Introduction Gastrointestinal medications can be broken down into the following categores antidiarrheals antiemetics H2 antagonists proton pump inhibitors other antiulcer medications laxitives Loperamide Also diphenoxylate Mechanism opiate compound uses normal constipating side effects of opiates to treat diarrhea available OTC (Imodium) Toxicity constipation drowsiness