Which OTC drug class is most associated with drowsiness and anticholinergic effects, especially in older adults?

• A. Decongestants
• B. Antihistamines (e.g., diphenhydramine)
• C. Analgesics
• D. Probiotics

Answer: (B)

Antihistamines, especially the first-generation ones like diphenhydramine, are known for causing drowsiness and anticholinergic effects. They block H1 receptors, which helps with allergy symptoms, but they also cross into the brain and produce sedation. At the same time, they block muscarinic acetylcholine receptors, leading to dry mouth, blurred vision, constipation, urinary retention, and cognitive effects. In older adults, these anticholinergic effects are more pronounced because aging changes how drugs are processed and how the brain responds, and because many medications are used together, increasing anticholinergic burden. That combination makes this class the most associated with drowsiness and anticholinergic effects in the elderly. Decongestants tend to cause stimulation rather than sedation, analgesics don’t typically produce anticholinergic effects, and probiotics don’t cause these symptoms.