Differential use of antidiabetic medication related to income, cohabitation and area of residence: a Swedish nationwide cohort study.

Background: Poor adherence to antidiabetic medication in individuals with type 2 diabetes (T2D) may lead to increased risk of morbidity and mortality. Socioeconomic and demographic factors associated with non-adherence have been mainly identified via cross-sectional studies. To investigate the association between antidiabetic medication adherence and income, cohabitation and area of residence.

Methods: Register-based cohort study of individuals with T2D living in Sweden and initiating antidiabetic treatment between 2006 and 2022. Confounding adjustment and competing events were accounted for via inverse probability of treatment and censoring weighting. Exposures were disposable income, social income support, cohabitation status and area of residence. Outcomes were antidiabetic medication adherence during the first year from treatment initiation and treatment interruption at 12 and 60 months.

Results: This study included 594 918 individuals with T2D. Low disposable income (adjusted OR: 1.18, 95% CI: (1.14 to 1.21)), social income support (1.09, (1.05 to 1.14)), living in large cities (1.28, (1.24 to 1.31)) and cohabitation (1.09, (1.06 to 1.11)) were associated with non-adherence (proportion of days covered ≤0.2), as compared with high adherence (proportion of days covered >0.8). Consistently, treatment interruption was associated with social income support (relative risk ratio at 12 months: 1.10, (1.06 to 1.14) and at 60 months 1.02 (1.00 to 1.05)), living in large cities (1.13, (1.12 to 1.14); 1.08, (1.07 to 1.08)) and low income (1.05, (1.03 to 1.07); 1.01, (1.00 to 1.02)).

Conclusions: Low income levels, cohabitation and living in large cities were associated with non-adherence to antidiabetic medication and risk of treatment interruption. The results highlight the need for targeted interventions aiming at improving adherence to treatments both at patient and healthcare system levels.