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Medication Mistakes: Types and Causes

What types of medication mistakes commonly occur in health care settings, and what are their causes?

The medication errors most frequently reported by health care professionals to a voluntary database involved failure to administer an ordered drug dose, improper drug dose or quantity, and drug prescribing errors. The leading causes of errors involved a general failure to act in accordance with education and training, failure to follow a procedure or protocol, and inaccurate or omitted transcription. Almost two of every 100 reported errors caused patient harm.

Slide For Medication Mistakes: Types and Causes
Slide For Medication Mistakes: Types and Causes
Slide For Medication Mistakes: Types and Causes

Why is this important?

Medication use involves a complex process that is subject to error at many points in health care settings. Medication errors are common in hospitals, occurring about once a day in the care of a typical hospital patient (IOM 2006).

  • A review of studies suggests that about one-half of medication errors in hospitals have the potential to harm patients, although only a small proportion actually cause patient harm (von Laue et al. 2003). (Medication errors that cause harm are called preventable adverse drug events.)
  • An estimated 1.5 million preventable adverse drug events occur in the U.S. each year, including 380,000 to 450,000 among hospital patients (IOM 2006). Although patient harm caused by medication errors is most often temporary in nature, in some cases the harm can be permanent or even fatal. Additional hospital treatment costs are estimated at $3.5 billion.


Among 823,268 voluntary reports from more than 775 health care organizations participating in a error reporting system during a five-year period (2000 to 2004), almost two of every 100 (1.7%) were associated with patient harm (Santell et al. 2005). Rates of harm were higher among reports from intensive care units (3.3%) and radiological services (12%).

  • The three most frequently reported types of medication errors—omission errors (failure to administer an ordered drug dose), improper drug dose or quantity (different from that prescribed), and drug prescribing errors—were cited in two-thirds (68%) of the reports in which error type was recorded.
  • The three types of reported errors that most frequently caused harm were wrong drug administration technique (e.g., incorrectly activating a drug administration system or not flushing an IV line), wrong route of drug administration (e.g., intravenous instead of intramuscular), and administering an improper dose or dispensing an improper drug quantity.
  • The three leading causes of errors—performance deficit (failure to act in accordance with education and training), failure to follow a procedure or protocol, and inaccurate or omitted transcription—were likewise cited in two-thirds (68%) of the reports in which a cause was recorded. Performance deficit was often cited in combination with other causes and contributing factors (e.g., distractions or staffing shortages).


Understanding the common types and causes of medication errors, along with information on the kinds of drugs involved (also captured in this reporting system), can help hospitals identify gaps in the medication use process. Reporting close calls or near misses—when patient harm might have occurred but didn't—can provide important clues about system vulnerabilities. This type of information can help hospitals improve systems and take other actions to help make patients safer.

Improvement Ideas and Resources

The Institute of Medicine (IOM 2006) recently made several recommendations for health care providers, payers, regulators, policymakers, and consumers to help prevent medication-related patient harm, including:

  • Strengthening patients' abilities to engage in medication self-management, such as through enhanced consumer information resources;
  • Adopting effective medication-error prevention strategies, such as electronic prescribing and clinical decision-support systems;
  • Improving the methods for labeling drugs and for communicating drug information to health care providers and consumers;
  • Establishing standards for drug-related health information technologies, such as specifications for effective drug safety alerting and prompting; and
  • Pursuing appropriate oversight and payment mechanisms to advance patient safety practices and professional competencies.
The recently enacted federal Patient Safety and Quality Improvement Act may promote better collection and analysis of information on medication errors by protecting the voluntary, confidential reporting of patient safety data to independent, certified patient safety organizations.

A 2004 self-assessment completed by 1,600 hospitals suggested increasing use of some of the 200 safe medication practices recommended by the nonprofit Institute for Safe Medication Practices. The Institute's Pathways to Medication Safety tool can help hospitals plan appropriate changes to improve patient safety in the hospital.


MEDMARX incorporates the taxonomy of the National Coordinating Council for Medication Errors Reporting and Prevention. A medication error is defined as "any preventable event that may cause or lead to inappropriate medication use or patient harm while the medication is in the control of the healthcare professional, patient, or consumer." Harm is defined as "impairment of the physical, emotional, or psychological function of structure of the body and/or pain resulting therefrom" (Santell et al. 2005).

During the 2000–2004 time period, MEDMARX permitted reporters to select one or more types of error from a predefined list of 11 to 13 error types (data in the chart on types of error represent 775,383 records associated with 831,863 reported types of error). Similarly, reporters could select one or more causes of error from a predefined list of 56 to 62 causes or error (data in the chart on causes of error represent 766,122 records associated with 1,301,534 reported causes of error).


Voluntary incident reporting typically does not capture the range of error and patient harm detected by other means such as direct observation or medical records (Flynn et al. 2002; Rozich et al. 2003). Hence, these data should be considered as one of several sources of information on this problem.


MEDMARX is an Internet-accessible, anonymous, voluntary national reporting program operated by U.S. Pharmacopeia, a nonprofit, independent standards-setting organization. More than 775 health care organizations (primarily hospitals and health care systems) reported data to MedMarx during the time period shown.


* Indicates source of data used in the chart(s).

Flynn, E. A., K. N. Barker, G. A. Pepper et al. 2002. Comparison of Methods for Detecting Medication Errors in 36 Hospitals and Skilled-Nursing Facilities.American Journal of Health-System Pharmacy 59 (5): 436–46.

IOM (Institute of Medicine). 2006. Preventing Medication Errors. Washington: National Academy Press.

Rozich, J. D., C. R. Haraden, and R. K. Resar. 2003. Adverse Drug Event Trigger Tool: A Practical Methodology for Measuring Medication Related Harm. Quality & Safety in Health Care 12 (3): 194–200.

*Santell, J. P., R. W. Hicks, and D. D. Cousins. 2005. Medmarx Data Report: A Chartbook of 2000–2004 Findings from Intensive Care Units and Radiological Services. Rockville, Md.: USP Center for the Advancement of Patient Safety.

von Laue, N. C., D. L. Schwappach, and C. M. Koeck. 2003. The Epidemiology of Preventable Adverse Drug Events: A Review of the Literature. Wiener klinische Wochenschrift. 115 (12): 407–15.