Omeprazole and Dark Green Stool Color
Omeprazole does not directly cause dark green stool discoloration as a recognized adverse effect. Dark green stool is not documented in the clinical pharmacology literature or safety profiles of omeprazole 1, 2, 3, 4, 5.
Understanding the Clinical Context
The most commonly reported gastrointestinal adverse effects of omeprazole are nausea and diarrhea, not stool color changes 1. When evaluating a patient presenting with dark green stool while taking omeprazole, consider alternative explanations:
Alternative Causes to Investigate
Dietary factors are the most common benign cause of green stool and should be explored first:
- Dark leafy greens (spinach, kale) containing chlorophyll
- Foods with green food coloring
- Iron supplementation (can cause dark green to black stool)
Gastrointestinal transit time affects stool color:
- Rapid transit through the GI tract can result in green stool due to insufficient time for bile pigment breakdown
- Diarrhea (which omeprazole can cause) may accelerate transit and contribute to green coloration 1
Concerning causes requiring evaluation:
- Upper GI bleeding should be ruled out, as dark stool can indicate melena (though typically black and tarry rather than green)
- This is particularly relevant since omeprazole is often prescribed for conditions involving GI bleeding risk 6
Clinical Approach
Immediate assessment should focus on:
- Detailed dietary history over the past 48-72 hours
- Medication review for iron supplements or other agents that alter stool color
- Assessment for signs of GI bleeding (hematemesis, melena, hemodynamic instability, anemia)
- Evaluation of stool consistency and associated symptoms (abdominal pain, fever, weight loss)
If concerning features are present (true melena appearance, anemia, hemodynamic changes, or alarm symptoms), proceed with appropriate workup including hemoglobin/hematocrit and consideration of endoscopy 6.
If benign causes are identified (dietary intake, rapid transit), reassurance is appropriate with follow-up if symptoms persist or worsen.