Background: Low health literacy is expected to be associated with medication non-adherence and early research indicated that this might be the case. Further research suggested that the relationship may be more equivocal.
Aim of the review: The goal of this paper is initially to clarify whether there is a clear relationship between health literacy and non-adherence. Additionally, this review aims to identify factors that may influence that relationship and ultimately to better understand the mechanisms that may be at work in the relationship.
Method: English language original research or published reviews of health literacy and non-adherence to orally administered medications in adults were identified through a search of four bibliographic databases (PubMed, EMBASE, CINAHL, and EBSCO Health).
Results: The search protocol produced 78 potentially relevant articles, of which 16 articles addressed factors that contribute to non-adherence and 24 articles reported on the results of research into the relationship between non-adherence and health literacy. Factors that contribute to non-adherence can be categorised into patient related factors, including patient beliefs; medication related factors; logistical factors; and factors around the patient-provider relationship. Of the 23 original research articles that investigated the relationship between non-adherence and health literacy, only five reported finding clear evidence of a relationship, four reported mixed results and 15 articles reported not finding the expected relationship. Research on possible mechanisms relating health literacy to non-adherence suggest that disease and medication knowledge are not sufficient for addressing non-adherence while self-efficacy is an important factor. Other findings suggest a possible U-shaped relationship between non-adherence and health literacy where people with low health literacy are more often non-adherent, largely unintentionally; people with moderate health literacy are most adherent; and people with high health literacy are somewhat non-adherent, sometimes due to intentional non-adherence.
Conclusion: It is clear that relevant research generally fails to find a significant relationship between non-adherence and health literacy. A U-shaped relationship between these two conditions would explain why linear statistical tests fail to identify a relationship across all three levels of health literacy. It can also account for the conditions under which both positive and negative relationships may be found.