Depression and medication adherence among breast cancer survivors: bridging the gap with the theory of planned behaviour.

Evidence suggests that more depressed breast cancer patients will less likely adhere to treatment plans. This study presents evidence that the theory of planned behaviour mediates the relation between depression and intentions to adhere to treatment plans and between depression and lack of adherence to medication regime. Two hundred and thirteen women undergoing breast cancer treatment participated in this study. Measures of depressive symptoms and planned behaviour variables were collected at the first time point; measures of medication adherence were collected at the second time point. Structural equation models were utilised to fit the data to the proposed models. Depressive symptoms were significantly correlated to both intentions and medication adherence. In support of hypotheses, the relation between depressive symptoms and treatment intention was mediated by attitudes towards health maintenance plans. The relation between depressive symptoms and medication adherence was fully mediated by the planned behaviour process. Conditions under which treatment intentions and perceptions of control in adhering to treatment were most related to medication adherence were elucidated. The results point to avenues for interventions to increase medication adherence among breast cancer patients. Manipulating attitudes and perceptions of control towards treatment plans will potentially serve to increase medication adherence.