anticholinergic
An anticholinergic is a drug that blocks acetylcholine at muscarinic receptors, effectively muting the parasympathetic nervous system. If parasympathomimetics turn up rest-and-digest, anticholinergics turn it down: drying secretions, speeding the heart, relaxing the gut and bladder, and dilating the pupil.
Strictly speaking these drugs are antimuscarinic; they are competitive antagonists that occupy the muscarinic receptor without activating it, so acetylcholine can no longer get through. The prototype is atropine, an alkaloid from deadly nightshade. Others are designed to stay local, such as inhaled ipratropium for the lungs or topical tropicamide for the eye.
Their uses span many specialties: drying secretions before surgery, speeding a dangerously slow heart, relieving bladder overactivity, easing intestinal cramps, dilating the pupil for eye exams, opening airways in COPD, and reducing tremor in Parkinson's disease. The flip side is the classic anticholinergic syndrome, and older people are especially prone to confusion.
Ipratropium, an inhaled anticholinergic, blocks muscarinic receptors in the airways to relax bronchial smooth muscle in chronic obstructive pulmonary disease.
An antimuscarinic bronchodilator for COPD.
Many drugs not labeled as anticholinergics, such as some antihistamines, tricyclic antidepressants, and antipsychotics, also block muscarinic receptors. Their combined anticholinergic burden is a major cause of confusion and falls in the elderly.