Does Hydroxyzine Have Anticholinergic Properties?
Yes, hydroxyzine definitively has anticholinergic properties, as explicitly stated in its FDA drug label, which lists "dry mouth" under the anticholinergic side effects category. 1
Direct Evidence from FDA Labeling
The FDA-approved drug label for hydroxyzine hydrochloride clearly categorizes anticholinergic effects as a distinct class of side effects, specifically identifying dry mouth as an anticholinergic adverse reaction. 1 This is not a theoretical concern but a documented pharmacological property of the medication.
Clinical Implications for Patients with SIBO and Motility Issues
In patients with SIBO and underlying motility disorders, hydroxyzine should be avoided or discontinued, as anticholinergic medications directly impair intestinal motility and can worsen bacterial overgrowth. 2
Why This Matters in SIBO:
The American Gastroenterological Association explicitly recommends immediately discontinuing all anticholinergic medications in patients with intestinal pseudo-obstruction and motility disorders, as these drugs directly inhibit intestinal motility. 2
Anticholinergic drugs impair autonomic regulation of colonic function, which is particularly problematic in older adults and those with pre-existing motility issues. 2
The migrating motor complex (MMC)—the small intestine's natural "housekeeping" mechanism that sweeps bacteria through the gut between meals—is disrupted by anticholinergic medications, creating ideal conditions for bacterial colonization and SIBO development. 3
Mechanism of Harm in SIBO Context
Anticholinergic effects slow gastrointestinal transit and reduce propulsive contractions, allowing bacteria to proliferate in stagnant loops of bowel. 3
The combination of reduced gut motility with anticholinergic drugs creates the perfect environment for anaerobic bacteria to colonize the small intestine. 3
Medications that impair motility should be systematically reviewed and discontinued before initiating SIBO treatment with antibiotics like rifaximin. 2, 4
Common Pitfall to Avoid
Do not assume that because hydroxyzine is primarily marketed as an antihistamine, its anticholinergic properties are clinically insignificant. The FDA label explicitly categorizes these effects, and gastroenterology guidelines specifically warn against anticholinergic use in motility-compromised patients. 2, 1
Alternative Considerations:
If antihistamine therapy is needed for allergic conditions in a SIBO patient, consider non-anticholinergic alternatives in consultation with the prescribing physician.
The American College of Gastroenterology emphasizes that offending medications must be discontinued before starting neostigmine or other prokinetic agents for motility disorders. 2