Purpose: The purpose of this study was to systematically review evidence regarding the association between regimen complexity and adherence.
Methods: Articles were searched in MEDLINE, LILACS, Cochrane, CINAHL, PsycINFO and references of included studies. Search terms included medication regimen complexity, medication adherence and their synonyms. Randomized clinical trials, cross-sectional, cohort or case-control studies published until March 2016 in English, Portuguese or Spanish were eligible if quantitatively examined the association between complexity and adherence in patients of any age and sex, under any type of medication therapy. Complexity was defined according to the strategy used to assess it in the individual studies. All types of instruments used to assess complexity and adherence were considered. Data extraction was performed using an electronic spreadsheet. Quality assessment was conducted independently using standard scales. The data were qualitatively synthesized.
Results: Fifty-four studies were included: 37 cross-sectional and 17 cohorts. Most were conducted in outpatient setting. Most frequently, studies were carried out with HIV-infected individuals or patients with chronic conditions. The most frequent methods used to assess complexity and adherence were complexity index (19) and self-report (27), respectively. Complexity was associated with adherence in 35 studies. Most of them (28) identified that participants with more complex regimens were less likely to adhere to pharmacotherapy; seven studies found a direct correlation. The others found inconclusive results or no association between complexity and adherence. The studies had low to moderate-methodological quality.
Conclusion: Although there was variability regarding the association between complexity and adherence, most studies showed that an increased regimen complexity reduces medication adherence.
Keywords: Medication adherence; Medication regimen complexity; Systematic review.