Adverse drug reaction

An adverse drug reaction (ADR) is an unintended medical event, which can potentially be associated with taking a medication. It can be disadvantageous or beneficial for the patient. ADRs may occur following a single dose or prolonged administration of a drug or may result from the combination of two or more drugs. The meaning of this term differs from the term "side effect" because side effects are proven by thorough investigation to have relationship to the drug. The study of ADRs is the concern of the field known as pharmacovigilance. An adverse event (AE) refers to any unexpected and inappropriate occurrence at the time a drug is used, whether or not the event is associated with the administration of the drug. An ADR is a special type of AE in which a causative relationship can be shown or is suspected. ADRs are only one type of medication-related harm. Another type of medication-related harm type includes not taking prescribed medications, known as non-adherence. Non-adherence to medications can lead to death and other negative outcomes. Adverse drug reactions require the use of a medication.