Which side effect is associated with TCAs?

• A. Nausea
• B. Insomnia
• C. Dry mouth
• D. Diarrhea

Answer: (C)

TCAs block muscarinic acetylcholine receptors, producing anticholinergic effects. The hallmark of this action is dry mouth (xerostomia) because saliva production is reduced when acetylcholine signaling is blocked. This makes dryness of the mouth the best-supported side effect among the choices. Other options are less typical: anticholinergic effects slow gut motility, so diarrhea is unlikely; nausea and insomnia can occur with various drugs but are not as specifically linked to TCAs as dry mouth. In practice, dry mouth is common and can be managed with hydration, sugar-free gum, or saliva substitutes, with extra caution in older patients who are more sensitive to anticholinergic burden.