Antimuscarinic agents block the actions of acetylcholine (Ach) through muscarinic receptors. They are classified as natural alkaloids like atropine, semi-synthetic derivatives, and synthetic compounds. Atropine stimulates many medullary centers and suppresses tremors, while hyoscine produces central nervous system depression. They cause dilation of the pupils, dry mouth, constipation, difficulty swallowing and talking, and increased heart rate by blocking muscarinic receptors in various organs and tissues. Common uses include as a pre-anesthetic to decrease secretions, to treat peptic ulcers, asthma, motion sickness, and parkinsonism.