What is the difference between a medication error and an adverse drug event?

A medication error is a preventable failure in the medication-use process that may or may not reach the patient, whereas an adverse drug event is harm from a drug; the overlap, an adverse drug event caused by an error, is called a preventable adverse drug event.

Where in the medication process do errors occur?

Errors can arise at prescribing, transcribing, dispensing, administration, or monitoring; prescribing and administration are frequently identified failure points, and the dominant causes are system factors such as poor information access and communication.

Medication Errors

A medication error is any preventable event that may lead to inappropriate medication use or patient harm while the medication is in the control of a health professional, patient, or consumer. Such errors can occur at any stage of the medication-use process, including prescribing, transcribing, dispensing, administration, and monitoring. Medication errors are among the most frequent and most studied causes of harm in health care, and only a subset cause actual harm, which is termed a preventable adverse drug event.

Definition

A medication error is a preventable failure in the medication-use process, at prescribing, dispensing, administration, or monitoring, that may lead to inappropriate medication use or patient harm; the subset that causes harm is a preventable adverse drug event.

Scope

This topic covers how medication errors are defined and classified by stage of the medication-use process, their relationship to adverse drug events, their causes within a systems framework, and what is known about their frequency. It is a reference and educational treatment of medication safety as a category of harm; it does not provide dosing, prescribing, or individualized treatment advice.

Core questions

How does a medication error differ from an adverse drug event, and what is a preventable adverse drug event?
At which stages of the medication-use process do errors most commonly arise?
Why does a systems analysis attribute most medication errors to process and design failures rather than individual carelessness?

Key concepts

Medication-use process (prescribing, transcribing, dispensing, administration, monitoring)
Adverse drug event versus medication error
Preventable adverse drug event
Potential adverse drug event (near miss)
High-alert medications
System causes of medication error

Key theories

Systems analysis of adverse drug events: Leape and Bates and colleagues showed that medication errors arise predominantly from failures in the systems supporting medication use, such as information access, communication, and process design, rather than from individual deficiencies, providing the rationale for system-level prevention strategies.

Mechanisms

Errors can enter at any stage of the medication-use process, but systems analysis has found that prescribing and administration are frequent points of failure and that the underlying causes are largely systemic, including inadequate access to drug and patient information, communication breakdowns, and poorly designed processes. Not every error reaches the patient or causes harm; many are intercepted (potential adverse drug events) or cause no injury, while those that do cause harm constitute preventable adverse drug events.

Clinical relevance

Medication errors are a leading category of preventable harm, and understanding their classification and system causes is fundamental to patient safety. This topic describes how medication-related harm is conceptualized and studied; it is not a source of dosing instructions or individualized treatment recommendations.

Epidemiology

Medication errors and adverse drug events are common across care settings. Hospital studies have documented frequent errors in intravenous and parenteral administration, including in intensive care, and ambulatory studies have found that adverse drug events affect a substantial fraction of outpatients, with many judged preventable or ameliorable. Reported rates vary with the detection method, the definitions used, and the stage of the process studied.

History

Medication safety was among the first areas of patient safety to be studied rigorously. Leape, Bates, and colleagues' 1995 systems analysis of adverse drug events established that such events stem largely from system failures, helping shift the field from individual blame toward process redesign. The Institute of Medicine's 2000 report reinforced medication errors as a prominent and partly preventable source of harm, and subsequent observational studies in inpatient, intensive care, and ambulatory settings refined estimates of their frequency.

Debates

How much medication-related harm is preventable?: Studies distinguish adverse drug events that follow appropriate use from those caused by error, but the boundary depends on definitions and reviewer judgement, so estimates of the preventable fraction vary, which complicates targeting and measuring prevention efforts.

Key figures

Lucian Leape
David Bates
Tejal Gandhi
Johanna Westbrook

Seminal works

leape-1995
gandhi-2003
kohn-corrigan-2000

Frequently asked questions

What is the difference between a medication error and an adverse drug event?: A medication error is a preventable failure in the medication-use process that may or may not reach the patient, whereas an adverse drug event is harm from a drug; the overlap, an adverse drug event caused by an error, is called a preventable adverse drug event.
Where in the medication process do errors occur?: Errors can arise at prescribing, transcribing, dispensing, administration, or monitoring; prescribing and administration are frequently identified failure points, and the dominant causes are system factors such as poor information access and communication.