Non-adherence to antihypertensive medication: The role of mental and physical comorbidity.

BACKGROUND: Multiple parameters influence adherence to drug treatment, including socio-economic, healthcare, condition, therapy, and patient-related factors. However, studies of the impact of patient-related factors, particularly regarding comorbid conditions, have produced conflicting results. OBJECTIVES: To analyse the association between mental and physical comorbidity and non-adherence to antihypertensive medication in patients attending primary care, after including a comprehensive range of chronic comorbidities and potential confounders. METHODS: Cross-sectional study of 113,397 adults with a diagnosis of hypertension in 2010 assigned to the public health service of a region in northeastern Spain. Pharmacy billing records were linked to data from electronic health records at individual level. Non-adherence was defined as an antihypertensive medication possession ratio (MPR) <80%. Multivariable logistic regression models were used to estimate the odds ratio for non-adherence. Potential predictors included mental and physical comorbidity, age, sex, blood pressure level, nationality, rurality, polypharmacy, and number of visits to the GP and to different specialties. RESULTS: One fifth of the study population showed poor adherence levels. Female sex, younger age, foreign nationality, living in a rural area, low blood pressure levels, polypharmacy, and mental comorbidity were positively and significantly associated with non-adherence. Conversely, non-adherence was negatively and significantly associated with the presence of cardiovascular risk factors and higher annual rates of GP visits. CONCLUSION: The majority of patient-related determinants identified here (e.g., the presence of mental comorbidity, polypharmacy, foreign nationality) underscores the need for a patient- rather than a disease-centred care approach, as well as adequate physician-patient communication.