What characterizes an adverse drug reaction (ADR)?

An adverse drug reaction (ADR) is primarily defined as an unintended and harmful reaction that occurs due to the administration of a medication. This reaction can manifest in various ways, such as through physical symptoms, psychological effects, or even exacerbation of existing conditions. The key characteristics of an ADR include its unintentional nature and the negative impact it has on the patient's health.

Unlike a beneficial side effect, which may provide a positive outcome, an ADR is inherently adverse and can require modifications in treatment or cessation of the drug altogether. While some drugs do have common side effects that might be expected across their usage, ADRs are specifically negative and not guaranteed to occur with all drugs; thus, stating that it's a common symptom for all drugs would misrepresent the definition. Finally, while some ADRs may indeed require medical attention, the defining feature is the harm or unintended effect on the patient, not necessarily that they demand immediate medical intervention.