To the Editor We are responding to the article by Coupland et al1 on the association of anticholinergic drug exposure with increased risk of dementia. The public attention to this report and potential to affect patient care call for a high level of scrutiny of the conclusions. Anticholinergic drugs, and particularly the often inattentive prescribing of these drugs, can result in preventable harm to patients, including exposure-related reversible cognitive impairment. However, if pharmacodynamically similar drugs are associated with different risks of irreversible dementia when prescribed for different indications, protopathic effects may be more likely. Similarly, weak evidence of an exposure-response association within indications decreases biological plausibility; patients prescribed but never meaningfully dosed with a drug are a type of control that has the disease (at least a mild case) but such low exposure to the drug as to raise mechanistic doubt about its potential to cause dementia.