Background: Adherence to psychotropic medication is still a concern to health care systems, mental healthcare professionals, researchers, and patients, as well. Recent literature on medication adherence increased focusing on the pervasiveness and significant impacts of adherence to medications. Purpose: The purpose of this scoping review is to identify the prevalence, contributing factors, methods of measurement, and interventions related to medication adherence among patients diagnosed with Major Depressive Disorders (MDD). Methods: Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) guideline was used. The scoping review involves the review, analysis, and synthesis of a broad scope of literature. Results: A total of 36 articles met the inclusion criteria for this scoping review. The prevalence of medication adherence among patients diagnosed with MDD ranged from 10.6% to 85.4%. About 67% of studies used self-reports as methods of data collection. Illness-related factors (e.g., the onset of the illness, duration of illness, symptoms, and illness severity), medication-related factors (e.g., adverse reactions, duration of treatment, cost of treatment), and patient-related factors (e.g., beliefs, attitudes, knowledge, self-stigma) were the most reported factors to associate with medications adherence. Also, the multi-faceted intervention has been recommended over a single-element intervention to enhance medication adherence. Conclusion: There is a need to select and integrate good assessment measures of medication adherence, which lead to providing better evidence on the outcomes, risk factors, and interventions to improve medication adherence.