Urinary incontinence can have a significant impact on patients' quality of life. Some causes involve physiologic and structural disorders of the urinary system. Other causes do not directly affect the urinary system but are related to difficulties in reacting to the urge to urinate or getting to the toilet alone, or an increase in urine output. Toxic substances or drugs are sometimes implicated. Drugs that affect one or more of the components of the normal continence mechanism expose patients to the risk of urinary incontinence. Some of these drugs act on the urinary system, particularly the autonomic nervous system; some increase urine output; some impair physical or cognitive function; and others cause urinary retention, leading to overflow incontinence. Drugs known to cause urinary incontinence are often prescribed for older patients, who are already at increased risk: sedatives, neuroleptics, antidepressants, cholinesterase inhibitors used in Alzheimer's disease, diuretics, alpha blockers used in hypertension or benign prostatic hyperplasia, and menopausal hormone replacement therapy.