We examined the independent associations between several psychological attributes and adherence to antihypertensive medication assessed by pharmacy refill records among hypertensive Finnish public sector employees. We found that only about 60% of the patients were totally adherent. High sense of coherence was associated with lower risk of being totally non-adherent. This association was found to be independent of factors that influenced adherence to antihypertensive medication, such as sociodemographic characteristics, health-related behaviours, self-reported medical history of doctor-diagnosed co-morbidity, and anteriority of hypertension status. We found no strong evidence to suggest that this association would be specific to certain types of antihypertensive drug, but the estimation was imprecise due to small numbers.
To our knowledge, this is the first study to depict quantitatively the relationship between several psychological attributes and adherence to antihypertensive medication. We found only one study to have examined previously the association between hostility and antihypertensive medication adherence 15
. Results from this multi-centre randomized double-blind study revealed that hypertensive men with high hostility scores were likely to report that they had trouble remembering to take their antihypertensive medications on a daily basis when compared to those with low hostility scores. However, the study assessed adherence by self-reports and hence could not eliminate the possibility that self-reports may be influenced by factors such as social desirability and introduce common method bias as personality was also determined based on self-reports in that study 28
A strength of the present study is the assessment of adherence using pharmacy refill records of antihypertensive medication rather than self-reported data. It is of great importance to specify whether patients actually filled their prescriptions, as the first step in adherence to a medication is to actually get that medication. 29
Second, we were able to control for a wide range of potential confounders that have been often found to be related to hypertension control 5
, including co-morbidity and anteriority of the hypertension status.
The association of SOC with lower non-adherence to antihypertensive medication is consistent with studies that have examined the influence of SOC on medication adherence for other pathologies. For example, a study 30
conducted among 65 participants with type 1 or type 2 diabetes found that SOC was related to better adherence which mediated the effect of SOC on glycemic control. Another study31
conducted among 99 patients undergoing antiretroviral therapy from an outpatient clinic found lower SOC to be related to more missed doses. Medication adherence is an important self-management activity and our results suggest that SOC might reflect a psychological factor underpinning adherence behaviour.
SOC was defined by Antonovsky18
as representing the salutogenic resources available to individuals. These resources, when strong, lead individuals to believe that what happens in life is predictable, and understandable (comprehensibility); that resources are available to help overcome difficulties as they arise (manageability); and that the demands created by exposure to difficulties are seen as challenges and are worthy of engagement (meaningfulness). Hence, persons with high SOC might perceive demands imposed by their hypertensive status as challenges, worthy of engagement, rather than as threats or stressors, and this might facilitate good adaptation to the disease and its treatment. SOC could be associated with better adherence because it may be a protective factor against demoralisation and may alleviate the development of psychological distress in the context of serious illness, such as hypertension.32
In this study, the five main classes of antihypertensive drugs available were: Antihypertensives (ACT-code C02), Diuretics (C03), Beta blocking agents (C07), Calcium channel blockers (C08) and Agents acting on the renin-angiotensin system (C09). The different classes may have distinct side effects and thus could potentially be differently related to psychological attributes. However, our results suggest that high sense of coherence was associated with better adherence in relation to most of the antihypertensive drugs. The results for Diuretics (C03) slightly differed, but small numbers prevent any definite conclusions.
Our findings should be interpreted in light of some limitations. First, although pharmacy refill records are objective measures and collected routinely, they do not represent a measure of whether the participants actually took the medications. It is possible that some of the participants characterized as totally adherent did not actually take their medication despite of filling their prescriptions, leading to overestimation of adherence in this study. Future research with alternative measures of adherence, such as pill counters, would provide an interesting comparison to the present results. Secondly, our sample of public sector employees did not include unemployed individuals and is thus not representative of the general population, which may limit the generalizability of our findings. Third, the SOC scale was included only in the survey for employees in the service of towns but not those working for hospitals; thus we had data only for 53% of the 1, 021 hypertensive participants identified. This limited statistical power in our analysis.
Implications of findings
The prevalence of full adherence to antihypertensive medication measured using pharmacy refill records in our sample of hypertensive patients was about 60% and the prevalence of those who really take their medication might be even lower. This confirms the fact that poor adherence to antihypertensive medication remains a major problem among patients with hypertension.2
Hypertension accounts for a significant cost burden through avoidable hospital admissions, premature deaths, work absenteeism, and reduced productivity. 33
In the WHO report 4
on adherence to long-term therapy, it has been recognized that patient’s behaviour is the critical link between a prescribed regimen and treatment outcome. The most effective regimen will fail if the patient does not take the medication as prescribed or refuses to take it. The relationship between sense of cohort and medication-adherence behaviour observed in this study suggests that knowledge (comprehensibility), capacity (manageability), and motivation (meaningfulness) may be important determinants of adherence behaviour in a context of asymptotic illness in which patients often do not feel or perceive the immediate consequences of skipping medication doses. Our results suggest that global messages on adherence to patients might benefit from emphasis on the importance of adherence (knowledge or comprehensibility), of their ability to achieve it (capacity or manageability), and focus on factors that influence their willingness to take the prescribed antihypertensive drugs (motivation or meaningfulness).
We assessed sense of cohort with a 13-item measure, but a validated brief 6-item scale also exists 34
. Although we acknowledge the high workload of clinicians, we believe that a brief assessment of sense of coherence could (in certain cases) provide clinicians with insight into patient behaviour and foster a more directed discussion regarding medication adherence with patients particularly low on sense of coherence. As adherence to medication is behaviour that is self-managed, interventions to promote better adherence to antihypertensive medication might benefit from input from the sense of coherence model because it provides specific aspects (meaningfulness, comprehensibility, manageability) that could be targeted in education programs 31
. Therapeutic education programs could be an important strategy to improve adherence by informing patients about hypertension, benefits of the treatment, and serious complications associated with non-adherence and by motivating and encouraging them to adhere to treatment. Education is also needed for self-management since most of the care provided for chronic conditions such as hypertension requires the patients to be involved in their own self care. 35