A patient with bipolar disorder, depression, and hypertension is taking multiple medications. Which medication is MOST likely to cause xerostomia (dry mouth)?

Correct answer: C. Amitriptyline (tricyclic antidepressant)

• A. Incorrect. Omeprazole is a proton pump inhibitor — it has minimal anticholinergic activity and rarely causes xerostomia.
• B. Incorrect. Hydrochlorothiazide (HCTZ) causes diuresis and can contribute to dry mouth indirectly (dehydration), but its anticholinergic effects are minor compared to tricyclics.
• C. Correct. AMITRIPTYLINE is a tricyclic antidepressant (TCA) with STRONG ANTICHOLINERGIC properties. Anticholinergic drugs block muscarinic receptors (M3) on salivary glands, dramatically reducing salivary flow, causing significant xerostomia. TCAs are one of the most common causes of drug-induced dry mouth.
• D. Incorrect. Lisinopril (ACE inhibitor) causes a nonproductive cough as its main oral/throat side effect — it does not typically cause xerostomia.