Medication beliefs mediate between depressive symptoms and medication adherence in cystic fibrosis

People with chronic medical conditions are at increased risk for depression and depressive symptoms (Clarke & Currie, 2009). This poses a threat to disease management and symptom control, with evidence from a range of chronic conditions spanning pediatrics through adulthood demonstrating that elevated depressive symptoms increase the risk for nonadherence approximately two-to threefold (DiMatteo Lepper, & Croghan, 2000; Grenard et al., 2011). Specific symptoms of depression, such as negative mood, low self-esteem, feelings of ineffectiveness, deficits in memory or energy, and more perceived barriers to adherence, may detract from adherence (Katon & Ciechanowski, 2002; McGrady & Hood, 2010). Ultimately, the association between depression and poor adherence translates to increases in disease symptoms, medical costs, morbidity, and mortality (Barth, Schumacher, & Herrmann-Lingen, 2004; Katon & Ciechanowski, 2002). The link between depressive symptoms and treatment adherence is well established, yet the mechanisms of this association are not well understood. Clarifying the processes by which depressive symptoms influence adherence would provide valuable direction for interventions to buffer the negative impact of depressive symptoms and ultimately improve health outcomes. Negative beliefs about prescribed medications (e.g., low self-efficacy to take medications, expectation of medications having null or negative outcomes, low motivation or intention to take medications) are possible mechanisms by which depressive symptoms could impede adherence. It is plausible that individuals’ depressive symptoms could influence their medication beliefs to be more negative, which may reduce the likelihood of adhering to prescribed medications. Individuals’ beliefs about medications are related to medication adherence. In a recent meta-analysis, Horne and colleagues (2013) reported that higher perceived need for treatment and fewer perceived concerns about treatments are significantly associated with better adherence. This holds across many conditions: Negative beliefs about treatments or medications have demonstrated associations with poorer adherence among individuals with HIV (Barclay et al., 2007), diabetes (Gherman et al., 2011), sleep apnea (Olsen, Smith, Oei, & Douglas, 2008), hypertension (Quine, Steadman, Thompson, & Rutter, 2012), and those recovering from stroke (Robinson-Smith, Johnston, & Allen, 2000) and chronic back pain (Glattacker, Heyduck, & Meffert, 2013). Studies evaluating medication beliefs as a potential mechanism linking depression and adherence have focused almost exclusively on one specific belief, self-efficacy; results indicate that medication self-efficacy mediates the links between depression and medication adherence for hypertension (Schoenthaler, Ogedegbe, & Allegrante, 2009) and HIV (Cha, Erlen, Kim, Sereika, & Caruthers, 2008) and between depression and glycemic control in Type 2 diabetes (Cherrington, Wallston, & Rothman, 2010). Few studies have examined the roles that other medication beliefs aside from self-efficacy play in the link between depressive symptoms and medication adherence. One exception demonstrated that not only lower self-efficacy but also more perceived barriers to taking medications were mediators of the indirect link between depressive symptoms and self-reported adherence in adults with diabetes (Chao, Nau, Aikens, & Taylor, 2005). More research examining a broader range of medication beliefs, including motivation, perceived importance, and outcome expectancies related to taking medications, is needed to fully understand the cognitive mechanisms by which depressive symptoms relate to adherence. Understanding the role that a comprehensive set of relevant medication beliefs plays in depressive symptoms and medication adherence has the potential to inform and guide clinical interventions to reduce depressive symptoms, support adaptive health-promoting beliefs, and facilitate optimal disease management. Cystic fibrosis (CF) is a chronic, progressive, obstructive lung disease with a complicated and demanding treatment regimen that includes multiple medications, nutritional guidelines, and chest physiotherapy, and can take several hours a day to complete (Sawicki, Sellers, & Robinson, 2009). In 1986, the median life expectancy was 27 years and less than 29% of individuals with CF were ≥18 years old in the United States, but with advances in drug therapies, this has changed dramatically (Cystic Fibrosis Foundation, 2013). In 2012, 49% of individuals with CF were adults and the median life expectancy was 41 years (Cystic Fibrosis Foundation, 2013). As adolescents and adults now account for over half of the CF population, there is growing attention to their health status and psychological and behavioral needs (Quon & Aitken, 2012). Depressive symptoms and medication nonadherence are emerging as significant risks for adolescents and adults with CF. Like other chronic conditions, the risk for depressive symptoms is elevated (Goldbeck, Besier, Hinz, Singer, & Quittner, 2010; Latchford & Duff, 2013; Riekert, Bartlett, Boyle, Krishnan, & Rand, 2007) and adherence to medications and other treatments is notably low (Briesacher et al., 2011; Eakin, Bilderback, Boyle, Mogayzel, & Riekert, 2011; Nasr, Chou, Villa, Chang, & Broder, 2013; Quittner et al., 2014). Despite these documented risks among people with CF and the known challenges to self-management, little is known about whether or how depressive symptoms relate to adherence to pulmonary medications for CF. One small study of adolescents with CF suggested that youths’ perceptions about their illness and treatments were related to self-reported adherence rates (Bucks et al., 2009), suggesting that beliefs about medications may be related to adherence to CF treatments. However, the role that CF-related medication beliefs play in depressive symptoms and adherence has not been explored, yet is a plausible mediator, given evidence suggesting such associations in other disease groups. No studies have examined a comprehensive set of disease-specific medication beliefs as a potential mechanism indirectly linking depressive symptoms with objectively measured medication adherence in adolescents and adults with CF or in any other chronic condition. Therefore, the aim of this study was to evaluate whether CF-related medication beliefs mediate the relationship between depressive symptoms and adherence to pulmonary medications. It was hypothesized that lower levels of positive medication beliefs, including lower self-efficacy, motivation, and perceived importance of and less optimistic outcome expectancies related to taking medications, would mediate the association between elevated depressive symptoms and suboptimal adherence as measured by 1 year of pharmacy refill data in individuals with CF.