Tiotropium is a M3 muscarinic receptor antagonist that acts on the airway smooth muscles, relaxing them producing bronchoconstriction. This is used in patients with asthma and chronic obstructive pulmonary disease. Common side effects of anti-muscarinic drugs are atropine-like side effects which include: Dry mouth, constipation, dry eyes, palpitations, difficulty in urinating, and altered mental status.