Can Mylanta Cause Diarrhea?
Yes, Mylanta (aluminum hydroxide/magnesium hydroxide) can cause diarrhea, primarily due to its magnesium component, which acts as an osmotic laxative and can induce secretory diarrhea when taken in sufficient quantities.
Mechanism of Diarrhea from Magnesium-Containing Antacids
The magnesium hydroxide in Mylanta causes diarrhea through several well-established mechanisms:
- Osmotic effect: Magnesium salts draw water into the intestinal lumen through osmotic forces, increasing stool water content and frequency 1, 2
- Dose-dependent relationship: For each millimole increase in fecal magnesium output, fecal weight increases by approximately 7.3 grams, demonstrating a direct quantitative relationship between magnesium intake and diarrhea severity 1
- Secretory mechanisms: Magnesium-containing antacids interfere with normal fluid absorption by affecting the Na+/K+ exchange pump and ATPase activity in enterocytes 3
Clinical Evidence and Prevalence
- Magnesium-containing antacids are explicitly listed among the drugs most frequently causing diarrhea, alongside antimicrobials and laxatives 2
- In patients with chronic diarrhea, excessive magnesium ingestion (from antacids or supplements) was identified as an important cause in 4.2% of cases 1
- Up to 4% of all chronic diarrhea cases may be medication-induced, with magnesium-containing products being a leading culprit 4
Diagnostic Considerations
When evaluating diarrhea in a patient taking Mylanta:
- Fecal magnesium measurement: Upper limits of normal are 14.6 mmol per day for fecal soluble magnesium output and 45.2 mmol per liter for fecal magnesium concentration 1
- Temporal relationship: Diarrhea typically appears during the first few days of treatment with magnesium-containing products 2
- Paradoxical effects: Excessive ingestion can lead to severe watery diarrhea, which may paradoxically cause hypomagnesemia due to massive magnesium losses 5
Important Clinical Caveats
- Aluminum counterbalances magnesium: The aluminum hydroxide component in Mylanta tends to cause constipation, which partially offsets the diarrheal effect of magnesium 4
- Individual variation: The net effect (diarrhea vs. constipation) depends on the relative proportions of aluminum and magnesium, individual patient sensitivity, and dosage 3
- Drug interactions: Mylanta should not be taken simultaneously with certain medications (such as azithromycin) as it reduces their absorption rate 4
Management Approach
If diarrhea occurs with Mylanta use:
- Discontinue or reduce dosage: Stop the antacid temporarily to confirm the relationship between Mylanta and symptoms 1, 2
- Switch formulations: Consider aluminum-only antacids if acid suppression is still needed, as these cause constipation rather than diarrhea 3
- Monitor for complications: Watch for dehydration, electrolyte imbalances (particularly hypomagnesemia if diarrhea is severe), and weight loss 2, 5
- Avoid expensive workup: A careful drug history can prevent unnecessary invasive diagnostic evaluations when magnesium-induced diarrhea is the cause 1