Adverse Drug Reaction

An adverse drug reaction (ADR) is an unwanted or harmful reaction experienced following the administration of a medication, or a combination of medications, under normal conditions of use that is suspected to be related to the medication. The reaction may be a known side effect of the medication or it may be a new previously unrecognised ADR.

The terms adverse drug reaction and adverse event are often used interchangeably but this is not always correct.

An adverse event (AE) is any undesirable event experienced by a patient while taking a medicine but may or may not be related to the medicine.

An example of an adverse drug reaction could be a patient developing a rash after taking a medicine whereas an example of an adverse event could be a patient visiting accident and emergency after falling off their bicycle during the period in which they are taking a medication.

Serious ADRs and AEs include those that are:

  • Fatal
  • Life-threatening
  • Disabling
  • Incapacitating
  • Result in or prolong hospitalisation
  • Congenital abnormalities and birth defects
  • Medically significant