What is the definition of an "adverse drug reaction"?

The definition of an "adverse drug reaction" encompasses any unintended harmful reaction that occurs following the administration of a medication. This definition highlights the importance of the term "unintended," signifying that the reaction is not a planned or expected outcome of treatment, but rather an adverse effect that may adversely impact a patient's health.

Identifying adverse drug reactions is crucial for patient safety and effective pharmacovigilance, as these reactions can lead to serious health consequences or compromise treatment efficacy. Unlike predicted side effects, which may be anticipated and communicated to patients, adverse drug reactions can vary significantly from patient to patient and may not be listed on the prescribing information.

In contrast, unwanted interactions with other medications are related to polypharmacy issues but do not solely define an adverse drug reaction. Predicted side effects are generally considered manageable or common reactions, rather than adverse reactions that primarily imply harm. Harmless side effects, while they can occur, do not qualify as "adverse" since they are benign and tend to resolve quickly, further distinguishing them from the broader and often more serious category of adverse drug reactions.