A patient taking amitriptyline (a tricyclic antidepressant) presents with xerostomia. What is the MOST likely cause?

Amitriptyline is a tricyclic antidepressant with significant anticholinergic effects, causing xerostomia by blocking muscarinic receptors on salivary glands. This is one of the most common drug-induced causes of dry mouth. When a known xerostomia-causing drug is present in the history and Sjögren's is not documented, the drug is the most likely cause. This follows clinical reasoning: always consider the drug history first when a clear pharmacological explanation exists.