Hydroxyzine Does Not Typically Cause Diarrhea
Hydroxyzine is not associated with diarrhea as a recognized adverse effect; instead, it causes anticholinergic effects that typically lead to constipation, not diarrhea. 1, 2
Primary Gastrointestinal Effects
The FDA drug label and clinical guidelines clearly document that hydroxyzine's anticholinergic properties cause:
- Dry mouth
- Constipation (not diarrhea)
- Inhibition of micturition
- Dry eyes 1
These anticholinergic effects slow gastrointestinal motility, which is the opposite mechanism needed to produce diarrhea.
Evidence from Overdose and Toxicity Studies
Even in overdose situations, diarrhea is not listed among the manifestations. The FDA label specifically states that overdose presents with hypersedation, convulsions, stupor, nausea and vomiting—but not diarrhea 2. A comprehensive toxicology study comparing hydroxyzine to diphenhydramine poisoning in over 17,000 cases found that hydroxyzine produces primarily CNS depression and fewer antimuscarinic effects than diphenhydramine, but again, diarrhea was not identified as a clinical feature 3.
Clinical Context
While general reviews note that over 700 drugs can cause diarrhea 4, and antihistamines are mentioned in broad drug categories 5, hydroxyzine specifically is not identified as a diarrhea-inducing agent in any of the provided evidence. The pharmacologic profile of hydroxyzine—with its anticholinergic and sedative properties—makes diarrhea mechanistically unlikely.
Clinical Recommendation
If a patient on hydroxyzine develops diarrhea, look for alternative causes rather than attributing it to the medication. Consider:
- Concurrent medications (antibiotics, magnesium-containing products, NSAIDs)
- Infectious causes
- Underlying gastrointestinal conditions
- Other medications in polypharmacy situations (common with hydroxyzine users 6)
The constipating effect of hydroxyzine may actually be therapeutically useful in patients with persistent rhinorrhea, though topical anticholinergics are generally preferred 1.