Iatrogenically induced cognitive deficits are common with pharmacological therapy. The deficits may range from gross encephalopathy with delirium to subtle subjective alterations (e.g., mood and perception of well being). The risks are increased for certain drug types, polypharmacy, the elderly, and patients with dementia or metabolic abnormalities. This review examines methodological concerns and the neuropsychological data on cognitive side effects across a variety of commonly used medicines in clinical practice.