Improving patient understanding of prescription drug label instructions.

BACKGROUND: Patient misunderstanding of instructions on prescription drug labels is common and a likely cause of medication error and less effective treatment. OBJECTIVE: To test whether the use of more explicit language to describe dose and frequency of use for prescribed drugs could improve comprehension, especially among patients with limited literacy. DESIGN: Cross-sectional study using in-person, structured interviews. PATIENTS: Three hundred and fifty-nine adults waiting for an appointment in two hospital-based primary care clinics and one federally qualified health center in Shreveport, Louisiana; Chicago, Illinois; and New York, New York, respectively. MEASUREMENT: Correct understanding of each of ten label instructions as determined by a blinded panel review of patients' verbatim responses. RESULTS: Patient understanding of prescription label instructions ranged from 53% for the least understood to 89% for the most commonly understood label. Patients were significantly more likely to understand instructions with explicit times periods (i.e., morning) or precise times of day compared to instructions stating times per day (i.e., twice) or hourly intervals (89%, 77%, 61%, and 53%, respectively, p < 0.001). In multivariate analyses, dosage instructions with specific times or time periods were significantly more likely to be understood compared to instructions stating times per day (time periods--adjusted relative risk ratio (ARR) 0.42, 95% Confidence Interval (CI) 0.34-0.52; specific times--ARR 0.60, 95% CI 0.49-0.74). Low and marginal literacy remained statistically significant independent predictors of misinterpreting instructions (low--ARR 2.70, 95% CI 1.81-4.03; marginal--ARR 1.66, 95% CI 1.18-2.32). CONCLUSIONS: Use of precise wording on prescription drug label instructions can improve patient comprehension. However, patients with limited literacy were more likely to misinterpret instructions despite use of more explicit language.