**Abstract**

Anticholinergic medications are widely used in older adults and are a common source of adverse events in this population. Common drug classes include antiarrhythmics, antidepressants, antiemetics, first generation antihistamines, urinary incontinence antimuscarinic agents, antiparkinsonian agents, antipsychotics, antispasmodics, and skeletal muscle relaxants. These drugs have been associated with delirium, cognitive impairment, sedation, dizziness, falls, fracture, constipation, urinary retention, blurred vision, tachycardia and dry mouth. If possible, these drugs should be avoided in older adults or less toxic agents within the class should be utilized. This chapter will explore the mechanism of action of anticholinergic drugs at both the cellular and organ system level; discuss how to assess for anticholinergic drug burden; list medications with anticholinergic effects as identified in the Beer's criteria on potentially inappropriate medication use in older adults; review anticholinergic drug–drug interactions; describe contraindications to the use of anticholinergic agents; and explore practical considerations such as the availability of these substances in nonprescription medications, their use at end of life and deprescribing.

**Keywords:** anticholinergic medications, Beer's criteria, adverse drug events, older adults, geriatrics

### **1. Introduction**

#### **1.1 Anticholinergic agents in nature**

Anticholinergic agents are substances that antagonize the effects of acetylcholine, a neurotransmitter formed by an ester of choline and acetic acid, that facilitates nerve impulses in both the central (CNS) and peripheral nervous systems. Acetylcholine is the main neurotransmitter of the parasympathetic system. It is also located within parts of the autonomic nervous system [1]. Anticholinergic agents are present in both pharmaceuticals and in nature. Substances like hyoscyamine and belladonna are naturally occurring anticholinergics which have been used medicinally to control gastric secretions, for irritable bowel symptoms, and for urinary spasms [2]. However, despite their natural origins, the use of these drugs is not without consequence and should be avoided in older adults.
