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| Journal of the New Zealand Medical Association,
28-November-2008, Vol 121 No 1286
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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.
MethodParticipants—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.
Results100 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
*p<0.001
DiscussionThe 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
References:
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