REPORTS Prescription drug warning labels 1048 Am J Health-Syst Pharm—Vol 63 Jun 1, 2006 REPORTS MICHAEL S. WOLF, PH.D., M.P.H., is Assistant Professor of Medicine, Institute for Healthcare Studies, Northwestern University, Chicago, IL. TERRY C. DAVIS, PH.D., is Professor of Medicine and Pediat- rics, Louisiana State University (LSU) Health Sciences Center— Shreveport. HUGH H. TILSON, M.D., DR.P.H., is Clinical Professor, Epidemiology and Health Policy, University of North Carolina at Chapel Hill. PAT F. BASS III, M.D., M.S., is Assistant Professor of Medicine and Pediatrics, LSU Health Sciences Center—Shreveport. RUTH M. PARKER, M.D., is Professor of Medicine, Department of Medicine, School of Medicine, Emory University, Atlanta, GA. Misunderstanding of prescription drug warning labels among patients with low literacy MICHAEL S. WOLF, TERRY C. DAVIS, HUGH H. TILSON, PAT F. BASS III, AND RUTH M. PARKER Address correspondence to Dr. Wolf at the Institute for Healthcare Studies, Northwestern University, 676 North St. Clair Street, Suite 200, Chicago, IL 60611 (mswolf@northwestern.edu). Thomas McGinnis is acknowledged for his guidance and com- ments on this article. Copyright © 2006, American Society of Health-System Pharma- cists, Inc. All rights reserved. 1079-2082/06/0601-1048$06.00. DOI 10.2146/ajhp050469 Purpose. The common causes for misun- derstanding prescription drug warning labels (PWLs) among adults with low liter- acy were studied. Methods. A total of 74 patients reading at or below the sixth-grade level and receiv- ing care at the primary care clinic at the Louisiana State University Health Sciences Center in Shreveport were recruited to par- ticipate in structured interviews. Patients were asked to interpret and comment on eight commonly used warning labels found on prescription medications. Correct inter- pretation was determined by expert panel review of patients’ verbatim responses. Qualitative methods were employed to code responses and generate themes re- garding the misunderstanding of these PWLs. Results. Among this sample of patients with low literacy skills, rates of correct inter- pretation for the eight warning labels ranged from 0% to 78.7%. With the excep- tion of the most basic label, less than half of all patients were able to provide adequate interpretations of the warning label mes- sages. Five themes were derived to de- scribe the common causes for misunder- standing the labels: single-step versus multiple-step instructions, reading difficulty of text, use of icons, use of color, and mes- sage clarity. Labels were at greater risk for being misunderstood if they included mul- tiple instructions, had a greater reading dif- ficulty, included unfamiliar terms, or used confusing icons that were discordant with text messages. Participants also frequently imposed an incorrect meaning on label col- ors, which led to further confusion. Conclusion. Patients with low literacy skills demonstrated a lower rate of correct inter- pretation of the eight most commonly used PWLs than did those with higher literacy skills. Multiple-step instructions, reading difficulty of text, the use of icons, the use of color, and message clarity were the com- mon causes of label misinterpretation. Index terms: Comprehension; Labeling; Patients; Prescriptions; Readability Am J Health-Syst Pharm. 2006; 63:1048- 55 N early half of the adult popula- tion in the United States lack the reading and numeracy skills required to process, understand, and act on health information. 1 Forty million U.S. adults are reading at the lowest levels of literacy proficiency and may have profound difficulty understanding health information for their own or a loved one’s needs. 2,3 Prior studies have linked low literacy to a poor understanding of one’s medical condition and nonad- herence to medical instructions. 4-7 Individuals with low literacy skills may be at particular risk for misun- derstanding information on phar- maceutical drug labels and package inserts, thus misusing these medica- tions. 8,9 Recent concern over patient safety has increased awareness of the poor quality of consumer informa- tion describing proper use of medi- cations and associated risks. 10,11 This has led to an expanded interest in the causes of medication-related errors, from a focus on physician or health care system failure to analysis of po- tential patient errors. 8-12 As health care delivery continues to shift from inpatient to outpatient settings, the burden of quality control over proper medication use will also shift from provider to patient. 1,9,13,14 An alarm- ing trend has already emerged as a result: between 1983 and 1993, there was a ninefold increase in deaths due to outpatient medication errors in