Journal of the New Zealand Medical Association, 28-November-2008, Vol 121 No 1286
Medication beliefs and adherence to antidepressants in primary care
Judith Russell, Nikolaos Kazantzis
Major depressive disorder is the most common mental health condition seen in primary care. The MaGPIe (2003) study,1 estimated a 12-month prevalence rate of 18.1% among primary care patients in New Zealand, with 4.4% meeting the criteria for severe depression. The economic burden of depression is heavy,² and the burden of depression experienced by the patient and their families is significant.3–5
It is widely accepted that primary healthcare providers deliver treatment for the vast majority of patients with mental health concerns.1,6 Antidepressant medication, such as serotonin-specific and serotonin and noradrenergic reuptake inhibitors are effective and frequently used treatments for the symptoms of depression.7–9 Research suggests that 40–70% of depressed patients adhere to medication.10
Recent research on the determinants of medication adherence has focused on patient beliefs or perceptions.11 This research has stemmed from the Self-Regulatory model which proposes that adherence is based on an “active decision” by the patient in response to their interpretation of the symptoms they experience. That is, the patient balances their concerns regarding the potential adverse effects of taking the medication with the benefits in deciding whether to adhere.12
Various theoretical models have been posited to explain patient adherence with medications, which may be understood as patient feedback or patient satisfaction with the benefits of the treatment versus the costs.13
The Beliefs about Medicines Questionnaire (BMQ) has been developed to assess patient’s medication beliefs about the potential costs and benefits of taking medication.14
A “depression specific” BMQ measure, consists of two constructs assessing the patient’s beliefs in the necessity of the medication for their health and their concerns about the adverse effects of the taking the medication (e.g. stigma, fear of dependency, and concerns about side effects). Patient’s perceived benefits of taking the medication is calculated in relation to the perceived harm using a necessity-concern differential on the BMQ.11,14 If the patient perceives that the benefits of taking the medication outweigh the costs or concerns, the differential is positive and adherence is predicted to be higher. In contrast, if the patient perceived that the costs of taking the medication are greater than the benefits, the differential is negative and adherence is predicted to be low.
Prior research has shown that the medication beliefs using the BMQ is predictive of medication adherence for patients suffering with asthma, renal disease, coronary heart disease and cancer,11 asthma,15 HIV/AIDS,16 haemodialysis,17 renal transplant recipients,18 and haemophilia.19
The present study was designed to examine the relationship between medication beliefs and adherence to antidepressant medication in primary care. It was expected that medication beliefs in depressed patients would be similar to those with chronic physical illness. Specifically, it was hypothesised that stronger beliefs about the necessity of antidepressants for the treatment of depressions measured by the BMQ would be associated with higher rates of adherence. It was also hypothesised that stronger beliefs about the potential adverse effects (concerns) of taking their antidepressants would be associated with lower rates of adherence.
A third hypothesis was that greater medication adherence would be observed when patients had stronger beliefs about the necessity of medication compared to their concerns about taking it (BMQ differential). Finally, we expected that patients who had more severe depressive symptoms would be less adherent to medication.
Participants—Depressed primary care patients were invited to participate in this study by their general medical practitioner at the end of a routine medical consultation. Due to the unique treatment adherence behaviours associated with adolescents,20 and older adults,21 inclusion criteria required that patients were between 18–65 years of age. Patients were also selected on the basis that they were prescribed antidepressant medication of the selective serotonin reuptake inhibitor type (SSRI), specifically for a DSM-IV-R diagnosis of major depressive disorder.
Patients were required to have taken their antidepressants for a minimum period of 6 weeks. This time period was to allow for a pattern of adherence behaviour to be well established at the time of assessment. A priori power analysis identified that 85 participants would be required to detect an effect size of r=0.30 (range r=0.21–0.4413,15,22,23) with 80% power, and an alpha criterion of 0.05.
Participants were aged between 21 and 64 years (mean=43.7, median=45.0, SD=11.49). Over half of the participants were female (n=61; 72%) and identified themselves as New Zealand European (n=72; 84%). A high percentage of participants stated that they had received education at tertiary or postgraduate levels (n= 49; 58%).
Measures—Information regarding gender, age, ethnic identity, and highest academic achievement were collected in order to describe the demographic profile of the sample. The general medical practitioners (GP) provided medication information including type and duration of treatment.
The Beliefs about Medication Questionnaire (BMQ)13 is a reliable and validated questionnaire for the assessment of medication beliefs. In the present study, a specific variation of the BMQ designed to assess medication beliefs a depressed population was employed (R Horne, personal communication, 2005).
This BMQ depression questionnaire consisted of two subscales. The first subscale consisted of five questions measuring the patient’s beliefs about the necessity of taking the antidepressants (e.g. “My health at the moment depends on these antidepressants” and “Without these antidepressants I would be very ill”). The second subscale consisted of fourteen questions measuring patients’ beliefs about the negative affects or concerns about taking the antidepressants (e.g. My antidepressants disrupt my life” and “I sometimes worry about the long-term effects of these antidepressants”). The BMQ’s psychometric properties have been demonstrated in previous studies.13,23
The Medication Adherence Report Scale (MARS) is a reliable and valid self report measure of non-adherence.22 The MARS was developed to reduce the problems of self-report bias with the development of scale items specifically related to non-adherent behaviours that were phrased in a non-threatening and non-judgemental manner.22 The MARS has been used in prior research including hospital outpatient samples with chronic pain and hypertension and was shown to have good psychometric properties (R Horne, personal communication, 2005).
The Beck Depression Inventory-Revised (BDI-II),24 is a widely used self-report measure of depressive symptoms The BDI-II contains 21 items to assess the severity of depression and has excellent data supporting its psychometric properties.25
Statistical methods—Data was analysed using Statistical Package for the Social Sciences (SPSS) for Windows (version 11) software. Descriptive statistical techniques were utilised to assess the central tendency variability and normality of the test variables. Due to the non-normal distributions of the study variables, non-parametric statistical analyses and a logarithmic transformation was conducted for the dependent variable (MARS scores).
Spearman correlations were used to establish the relationship between medication beliefs and self reported adherence. Due to the uneven number of items in the two BMQ subscales (necessity and concern), the individual scale totals were converted to standardised Z scores. The concern score was then subtracted from the necessity score to give the BMQ differential for each participant.
100 questionnaires were distributed to 15 GPs in the Auckland region; 3 questionnaires were returned unanswered, 6 participants who did not meet the selection criteria were excluded from data analysis, and 6 patients who produced statistically significant outliers or missing data were also excluded. Missing data were not imputed. A total data of 85 participants were included in the final dataset for analysis.
Participants in the present study reported high levels of medication adherence. Fifty-four percent (n= 46) had a score above the median (total score of 24 or more) on the MARS (possible range 5-25). Over half of the sample (51%) reported “minimal” symptoms of depression or less as assessed by the BDI-II. The remaining 49% of the sample reported “mild” or “moderate” depressive symptoms and 13% reported “severe” symptoms.
Table 1 shows the Spearman correlation coefficients used to detect the strength and direction of relationship between medication beliefs, depression, and adherence. These correlations indicate that there is no significant relationship between beliefs in the necessity of medication and adherence with antidepressants. However, high scores on the BMQ concern subscale were positively associated with non-adherence.
In addition, where beliefs about the necessity outweighed concerns about taking the medication (BMQ differential), significantly greater adherence was observed. Finally, greater depressive symptomatology was associated with non-adherence.
Table 1. Correlations between medication beliefs and adherence
The findings from this study suggest that medication beliefs of depressed patients are consistent with the medication beliefs of those with chronic physical illness. Specifically, adherence to medication was higher for those participants with lower concerns about taking the medication. Furthermore, adherence was greatest in participants whose perceived need for medication exceeded their concerns about taking the medication.
The significant correlation detected between stronger levels of concerns about taking antidepressants and levels of adherence deserves further attention. Questions on the BMQ concern scale relating to stigma and concern with other people’s impressions of antidepressant medication, were the most strongly endorsed questions in the scale. This finding differs from AIDS related research where items rating concern about the long-term effects, side effects and disruption to life were the most strongly endorsed.16
Theoretical models predict that the views of others influence the performance of health behaviours such as medication adherence. Depression is the subject of considerable social stigma with many regarding depression as a sign of personal weakness. Thus, the detection of a significant correlation between levels of concern and adherence suggests social stigma may be an important factor in adherence to antidepressants in New Zealand.
The lack of correlation between necessity beliefs and adherence is also interesting. Taking into consideration the theoretical background of the study and the high level of adherence reported by this participant group, we predicted that high adherence is related to stronger belief in necessity beliefs. Whilst there are limitations to the design of this study, one interpretation of this finding might be that as a group, depressed patients have low levels of belief in the necessity of medication. Indeed, this interpretation would be consistent with prior research showing non-adherence with antidepressants can be due to perceived necessity.26
The statistically significant correlation between the “BMQ differential” and adherence is similar to other research findings suggesting that adherence may result from a risk-benefit analysis where beliefs about the necessity of medication to treat depression are balanced against the concerns about adverse effects.
Certain limitations of the present study should be acknowledged. As detailed in the results, the sampling procedure inadvertently resulted in the recruitment of a highly adherent group of patients. This may have been attributed to a selection bias on behalf of patients and GP’s and limits the extent to which the findings can be considered representative of primary care in New Zealand. In other words, it is possible that the relationships identified in the present study are only applicable to a highly compliant depressed population.
A prospective study where medication beliefs are measured at the outset of therapy and monitored during the course of therapy alongside adherence would take account of the methodological limitation in the present study and prior research on medication adherence. 27 Assessment of a depressed sample with more severe and complex depression presentations and the nature of the doctor-patient relationship would also provide valuable information, and may account for a greater proportion of the variance in the relationships between beliefs and adherence.
It should also be acknowledged that although the adherence measure used in the present study was developed to minimise the potential for bias, it was still a self report measure and the use of multiple measures of treatment adherence in research is highly recommended (e.g., medication counts).28
In conclusion, findings of the present study support the hypothesis that medication beliefs of depressed patients are important in determining adherence with antidepressant treatment. These preliminary results also indicate that perceived social stigma could be important in determining adherence with antidepressants.
The practical implications for those prescribing antidepressant therapies are twofold: assessing patient beliefs about the necessity of the medication, and assessing patient concern about potential adverse effects are likely to provide important indicators of adherence, and by implication prognosis for therapy. This research would suggest that concerns about social stigma might be a particularly important factor for those deciding to begin antidepressant therapy in New Zealand.
Further research examining whether treatment beliefs prospectively predict treatment adherence and outcome is required. Research investigating the effects of tailoring regimens to patients’ beliefs is also warranted.
Competing interests: None known.
Author information: Judith Russell, Clinical Psychologist, Whirinaki, Child and Adolescent Mental Health Services, Counties Manukau District Health Board, Manukau, Auckland; Nikolaos Kazantzis, Senior Lecturer and Registered Clinical Psychologist, School of Psychology, Massey University, Auckland and Rodney Adult Mental Health Team, Waitemata District Health Board, Takapuna, Auckland
Acknowledgements: The present study represented a Masters-level research project completed by the first author under supervision of the second author at Massey University, Auckland campus. We thank Dr Robert Horne at the University of London for permission to use the BMQ. We also thank the GPs for their support and willingness to recruit participants for this study. The GPs that participated in the present study were Drs Mark Arbuckle, Peter Bowden, Raymond Chan, Peter Clemo, Ivan Connell, Cathy Ferguson, William Ferguson, Janet Frater, Kirsty Gendall, David Going, Wee-Ling Koo, Andrew Lawson, James Lello, Richard Mercer, and John Russell. Special thanks go to the participants for giving their time to complete the questionnaires. Finally, we thank Dr Dave Clarke, Massey University for comments on a previous version of this paper.
Correspondence: Dr Nikolaos Kazantzis, School of Psychological Science, La Trobe University, Melbourne, Victoria 3086, Australia. Fax: +61 (0)3 94791956. Email: Nikolaos@NikolaosKazantzis.com
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