OBJECTIVE:

To examine the nature and cause of patients' misunderstanding common dosage instructions on prescription drug container labels.

METHODS:

In-person cognitive interviews including a literacy assessment were conducted among 395 patients at one of three primary care clinics in Shreveport, Louisiana, Jackson, Michigan and Chicago, Illinois. Patients were asked to read and demonstrate understanding of dosage instructions for five common prescription medications. Correct understanding was determined by a panel of blinded physician raters reviewing patient verbatim responses. Qualitative methods were employed to code incorrect responses and generate themes regarding causes for misunderstanding.

RESULTS:

Rates of misunderstanding for the five dosage instructions ranged from 8 to 33%. Patients with low literacy had higher rates of misunderstanding compared to those with marginal or adequate literacy (63% versus 51% versus 38%, p<0.001). The 374 (19%) incorrect responses were qualitatively reviewed. Six themes were derived to describe the common causes for misunderstanding: label language, complexity of instructions, implicit versus explicit dosage intervals, presence of distractors, label familiarity, and attentiveness to label instructions.

CONCLUSION:

Misunderstanding dosage instructions on prescription drug labels is common. While limited literacy is associated with misunderstanding, the instructions themselves are awkwardly phrased, vague, and unnecessarily difficult.

PRACTICE IMPLICATIONS:

Prescription drug labels should use explicit dosing intervals, clear and simple language, within a patient-friendly label format. Health literacy and cognitive factors research should be consulted.