This meta-analysis examines the relationship between depression and treatment nonadherence in patients with type 1 and type 2 diabetes. The study found a significant association between depression and nonadherence to diabetes treatment, with a weighted effect size of r = 0.21 (95% CI 0.17-0.25), indicating a medium effect. The effect was stronger in studies where self-care was measured as a continuous variable rather than a categorical one. The strongest effects were observed for missed medical appointments and composite measures of self-care, while the weakest effects were found for foot care, which was not statistically significant. Moderation analyses revealed that studies with stronger methodologies showed larger effects. The relationship between depression and nonadherence was also influenced by the type of self-care measured, with the strongest effect for missed medical appointments. The study also found that children and adolescents had larger effects for glucose monitoring compared to adults, although this did not reach statistical significance. The results suggest that depression is significantly associated with nonadherence to diabetes self-care, with moderate effect sizes. The findings indicate that depression may be a pathway to worse diabetes outcomes through impaired self-care. The study highlights the importance of considering depression in diabetes management and suggests that interventions targeting both depression and self-care could be more effective. The study also emphasizes the need for more rigorous measures and avoiding dichotomization of variables to improve the accuracy of effect size estimates. Overall, the study provides important insights into the relationship between depression and diabetes self-care, highlighting the potential for targeted interventions to improve outcomes in patients with diabetes.This meta-analysis examines the relationship between depression and treatment nonadherence in patients with type 1 and type 2 diabetes. The study found a significant association between depression and nonadherence to diabetes treatment, with a weighted effect size of r = 0.21 (95% CI 0.17-0.25), indicating a medium effect. The effect was stronger in studies where self-care was measured as a continuous variable rather than a categorical one. The strongest effects were observed for missed medical appointments and composite measures of self-care, while the weakest effects were found for foot care, which was not statistically significant. Moderation analyses revealed that studies with stronger methodologies showed larger effects. The relationship between depression and nonadherence was also influenced by the type of self-care measured, with the strongest effect for missed medical appointments. The study also found that children and adolescents had larger effects for glucose monitoring compared to adults, although this did not reach statistical significance. The results suggest that depression is significantly associated with nonadherence to diabetes self-care, with moderate effect sizes. The findings indicate that depression may be a pathway to worse diabetes outcomes through impaired self-care. The study highlights the importance of considering depression in diabetes management and suggests that interventions targeting both depression and self-care could be more effective. The study also emphasizes the need for more rigorous measures and avoiding dichotomization of variables to improve the accuracy of effect size estimates. Overall, the study provides important insights into the relationship between depression and diabetes self-care, highlighting the potential for targeted interventions to improve outcomes in patients with diabetes.