Understanding initial medication adherence amongst major depressive disorder patients: A scoping review

Initiation of medication, or the first step in adherence, is a critical determinant of pharmacotherapy success in major depressive disorder (MDD). However, inconsistencies in defining and measuring initiation pose challenges in understanding its impact on patient outcomes.

This scoping review aims to systematically assess the definitions, operationalization, and measurement of initial medication adherence (IMA) among patients with MDD.

A literature search was conducted across PubMed, Embase, Scopus, and PsycInfo from inception to March 2025. Studies were included if they defined, measured, and evaluated IMA among patients with MDD prescribed selective serotonin reuptake inhibitors or serotonin-norepinephrine reuptake inhibitors.

Out of 1,636 studies, 13 met the inclusion criteria. Definitions of medication initiation varied, with durations ranging from 4 to 27 weeks. Measurement approaches included prescription claims, self-report, pill counts, and electronic monitoring. The operationalization of adherence status during the IMA phase lacked standardization, with studies using different adherence thresholds to define whether a patient was considered adherent. Factors associated with initiation included patient demographics, prior antidepressant use, provider specialty, and socioeconomic factors.

This review found high variability in the definition and evaluation of IMA in MDD. A more standardized and consistent approach is needed to define, operationalize, and evaluate IMA, considering the pharmacologic aspects of first-line therapies for MDD.