StATS: What is an adverse reaction? (adverse drug reaction)

There is no common definition of adverse reaction, though most definitions make an attempt to distinguish this term from adverse event and side effect. Here is a haphazard sampling of some definitions:

All medications administered for therapeutic or diagnostic purposes can be associated with unintended consequences or side effects. When this problem occurs, the untoward event is referred to as an adverse drug reaction.

An adverse reaction to a drug has been defined as any noxious or unintended reaction to a drug that is administered in standard doses by the proper route for the purpose of prophylaxis, diagnosis, or treatment.

The last source goes on to define reactions that may occur in anyone (drug overdose, drug side effect, drug interaction) and reactions that occur only in susceptible subjects (drug intolerance, drug idiosyncracy, drug allergy, and pseudoallergic reaction).


In a study of drugs used in obstetric patients, researchers noted adverse drug reactions (ADR's), as classified by Kramer's algorithm. The results were:

Of the 207 patients, an ADR was positively classified in 25 cases (12.1%, CI95% 8.1 to 17.5%). All ADR's were classified as minor reactions. -- Drug therapy and adverse drug reactions to terbutaline in obstetric patients: a prospective cohort study in hospitalized women. Hernández-Hernández DM, Vargas-Rivera MJE , Nava-Ocampo AA, Palma-Aguirre JA, Sumano-López H. BMC Pregnancy and Childbirth 2002, 2:3 doi:10.1186/1471-2393-2-3. [Medline] [Abstract] [Full text] [PDF]

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