Abstract
The prevalence of harms in healthcare related to drug treatment is often quantified using terms developed for pharmacovigilance and pharmaceutical care. In this overview, we guide through the definitions and the settings for which they were developed, with the underlying intention to facilitate the interpretation of hitherto available research intended to contribute information regarding the magnitude of the problem in healthcare and to provide guidance for future research. To start, the regulatory/academic definitions of an adverse drug reaction (ADR) and a drug-related problem (DRP) are considerably broader than a literal interpretation would suggest. ADRs are defined for the pharmacovigilance setting, and for drug safety reasons the opposite of the benefit of the doubt rules; if it cannot be excluded that the medication has caused or contributed to an event, it will be a suspected ADR. DRPs represent the pharmaceutical care setting where every aspect is included that could potentially be problematic; a manifested problem is not required. When quantifying the prevalence of harms related to drug treatment in the healthcare setting, however, it may not be considered reasonable to count every circumstance that could possibly be an ADR or everything that could potentially be problematic. Therefore, definitions developed for the pharmacovigilance and the pharmaceutical care settings are not fully applicable to estimate the magnitude of drug treatment problems in healthcare. Proposed guidance for the future includes cautious interpretation of research results, as well as a conscious choice of definitions according to purpose and tempered reporting in research.