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Definitions and Understanding of ADRs & AE

Adverse Drug Reaction:

We define an adverse drug reaction as “an appreciably harmful or unpleasant reaction, resulting from an intervention related to the use of a medicinal product, which predicts hazard from future administration and warrants prevention or specific treatment, or alteration of the dosage regimen, or withdrawal of the product.”


In the pre-approval clinical experience with a new medicinal product or its new usages, particularly as the therapeutic dose(s) may not be established: all noxious and unintended responses to a medicinal product related to any dose should be considered adverse drug reactions. 

The phrase “responses to a medicinal product” means that a causal relationship between a medicinal product and an adverse event is at least a reasonable possibility, i.e. the relationship cannot be ruled out. 

Regarding marketed medicinal products, a well-accepted definition of an ADR in the post marketing setting is found in WHO Technical Report 498 (1972) and reads as follows: 

Unexpected adverse drug reaction: An adverse reaction the nature or severity of which is not consistent with the applicable product information (e.g. the Investigator Brochure for an unapproved investigational medical product).

Adverse events are defined as “serious” based upon patient event outcome or action criteria usually associated with events that pose a threat to a patient’s life or functioning. Seriousness (not severity) serves as a guide for defining regulatory reporting obligations. 

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