General

An adverse drug reaction (ADR) is any unexpected, undesired, or excessive response to a medication that results in:

• temporary or permanent serious harm or disability
• admission to a hospital, transfer to a higher level of care, or prolonged stay
• death.

Adverse drug reactions are distinguished from adverse drug events, in which causality is uncertain, and side effects, which may be bothersome to the patient and necessitate a change in therapy but are not considered serious. Although some ADRs are the result of medication errors, many are not.