Anticholinergic drugs block the effects of acetylcholine at muscarinic receptors in the central and peripheral nervous system. Prototype anticholinergic is atropine, which is highly selective for muscarinic receptors. Anticholinergic drugs have many therapeutic uses including treatment of Parkinson's disease, motion sickness, respiratory disorders, ophthalmological disorders, and poisonings. However, they can cause adverse effects such as dry mouth, blurred vision, tachycardia, constipation, and delirium at high doses.