Discussion
This systematic review and meta-analysis determined the pooled
proportion of non-adherence to anti-diabetic medications and synthesized
the associated factors with medication non-adherence among individuals
with diabetes. Based on the MMAS-8, the MMAS-4, and self-care tools, the
proportion of non-adherence to anti-diabetic medication was reported at
different ranges. We found the pooled proportion of non-adherence to
anti-diabetic medications using the MMAS-8, MMAS-4 and cut-off at 80 or
90% scale was 43.4%, 29.5% and 29.1%, respectively Evidence from
previous research reported that the rates of non-adherence to prescribed
anti-diabetic regimens among individuals with diabetes ranged from 9%
to ˃80% 5, which is in
line with current findings. In addition, another review on adherence to
medication among individuals with type 2 diabetes reported that average
adherence to anti-diabetic medication ranges from 36% to 93%4. However, earlier
reviews were predominantly focused on adherence with diabetes medication4,57,
factors affecting medication adherence among patients with diabetes58,59,
and economic consequences of mediation adherence in diabetes60.
Failure to adherence to prescribed medication regime is seen as a
serious issue resulting in negative impact on individuals’ health and
health care system. There is, thus, a need to identify specific barriers
that will help in adopting suitable techniques to overcome them and
improve medication adherence. Previous studies reported various factors
of medication non-adherence among individuals with diabetes, such as the
severity of disease, demographic factors and socioeconomic status58. This study
attempted to collate factors affecting non-adherence from each of the
five groups, including disease, therapy, healthcare, patient, and
socioeconomic factors, which would have wide generalizability. Results
from current study advocates that patient-related factors were
consistently related to non-adherence. Patients having high BMI and low
concerns were related to non-adherence. Further, non-adherence was
consistently associated with socioeconomic factors, such as low
education and being employed in our review. Similar findings were also
reported in previous studies where association between education and
non-adherence reported25. It has been
reported that low education level can interfere with knowledge of the
disease and medication to some extent26. Considering
potential gap between education and disease awareness, educational
research is urgently warranted to identify effective strategies to
assist individuals with diabetes in medication adherence.
Patient’s knowledge about disease and associated factors could play a
pivotal role for better compliance with treatment strategy. This study
found that non-adherence was related with condition related
characteristics. Individuals suffering from depression was consistently
associated with non-adherence to anti-diabetic medication in current
study which is in accordance with findings from prior studies61,62.
For instance, a study by Grenard and colleague reported that individuals
with depression were 1.76 more likely to be non-adherent to taking
medication for chronic diseases than patients without depression62. Therapy-related
factor was yet another factor consistently associated with non-adherence
in our review. Drug regimen complexity, i.e., taking multiple daily
doses was found to be a critical factor for non-adherence to medication.
This finding is consistent with that found in a previous review that
showed adherence is inversely associated with the number of medication
doses per day 63. This
suggests that clinicians should be aware of the fact that access to
simplified dosage regimens by patients may be important aspect in
maximizing therapeutic success.
Lastly, healthcare system factors were consistently related to
non-adherence in our review. We found that poor doctor-patient
relationship was associated with medication non-adherence in individuals
with diabetes and aligns with findings from a prior review64, suggesting that
doctor-patient relationship quality is a potentially important point of
intervention to improve medication adherence. Indeed, the
provider-patient relationship plays a major role in keeping the patient
well informed about their medications, which directly influences the
adherence 65. In the
present study, dissatisfaction with communication was another healthcare
system factor associated with non-adherence. This finding is consistent
with a prior study about aspects of patient-provider communication and
medication adherence in diabetes66. Future studies
should investigate whether improving communication skills among
providers with poorer patient communication ratings could improve their
anti-diabetic medication adherence and outcomes. In addition, some
factors such as poor knowledge, self-efficacy, young adulthood age,
unmarried, low income, having more comorbid conditions, being
hypertensive, having adverse side effects and complex medication regime
had inconsistent relationships with non-adherence to anti-diabetic
medications across studies. Similar results was also reported in the
previous studies15,37,67.
We used a comprehensive search strategy to identify all eligible studies
and attempted to increase the quality of the included studies by using
well-defined eligibility criteria. The overall quality of the included
studies was acceptable and meeting all the specified criteria. However,
current study has some limitation as it was restricted to papers written
in the English language only, contributing to potential publication
bias. It was not possible to quantitatively pool data from all 43
studies that were identified for the systematic search and this could
reduce the generalizability of findings. There was a high heterogeneity
between the included studies due to differences in assessment
methodologies. Further, we were unable to obtain pooled estimates of the
strength of association of each factor. Nevertheless, our extensive
summary of the factors associated with non-adherence will be useful when
designing interventions to combat non-adherence in future research.