The prevalence of negative clinical outcomes was 33%, of which more than 73% of these were preventable. Factors associated with their appearance were age, number of medicines, and their combined effect.

A multitude of terms and definitions are used in patient safety related to medication. This heterogeneity makes it difficult to compare the results among studies and to appreciate the true magnitude of the problem. Classifying and unifying the terminology is necessary to advance in patient safety strategies.

NCOMs provoked approximately one-third of visits to the EDs, and a high percentage of these were preventable. Implementation of strategies for patient safety and pharmaceutical care could help to prevent these problems and optimize the use of medications.