Medication guides are required documents to be distributed to patients in order to convey serious risks associated with certain prescribed medicines. Little is known about the effectiveness of this information to adequately inform patients on safe use.

To examine the readability, suitability, and comprehensibility of medication guides, particularly for those with limited literacy.

Assessments of suitability and readability of 185 medication guides, and a sub-study examining change in suitability and readability from 2006 to 2010 among 32 of the medication guides (Study 1); ‘open book’ comprehension assessment of medication guides (Study 2).

Two general internal medicine clinics in Chicago, IL.

Four hundred and forty-nine adults seeking primary care services, ages 18–85.

For Study 1, the Suitability Assessment of Materials (SAM) and Lexile score for readability. For Study 2, a tailored comprehension assessment of content found in three representative medication guides.

The 185 analyzed medication guides were on average 1923 words (SD = 1022), with a mean reading level of 10–11th grade. Only one medication guide was deemed suitable in SAM analyses. None provided summaries or reviews, or framed the context first, while very few were rated as having made the purpose evident (8 %), or limited the scope of content (22 %). For Study 2, participants’ comprehension of medication guides was poor (M = 52.7 % correct responses, SD = 22.6). In multivariable analysis, low and marginal literacy were independently associated with poorer understanding (β = –14.3, 95 % CI –18.0 – –10.6, p < 0.001; low: β = –23.7, 95 % CI –28.3 – –19.0, p < 0.001).

Current medication guides are of little value to patients, as they are too complex and difficult to understand especially for individuals with limited literacy. Explicit guidance is offered for improving these print materials.