Table 1. Inclusion and Exclusion Criteria .

MMT: Methadone Maintenance Treatment

Criteria	Inclusion Criteria	Exclusion Criteria
Population	Studies involving elderly individuals (aged 60 and above) undergoing MMT.	Studies do not focus on elderly populations (aged 60 and above).
Intervention	Studies examining methadone maintenance treatment as the primary intervention for opioid dependence. Studies that may include MMT in combination with other interventions, provided the effects of MMT are reported separately.	Studies that do not include methadone maintenance treatment as a primary intervention. Studies focused solely on other forms of opioid substitution therapies without including MMT.
Outcomes	Studies reporting on mortality rates among elderly individuals on MMT. Studies identifying factors associated with mortality in this population, such as comorbid conditions, duration of treatment, and adherence.	Studies that do not report on mortality rates or factors associated with mortality. Studies that focus exclusively on other outcomes such as quality of life, drug use patterns, or psychosocial outcomes without addressing mortality.
Study Design	Cohort studies, case-control studies, randomized controlled trials, and longitudinal studies. Systematic reviews and meta-analyses provide comprehensive data on the topic.	Cross-sectional studies, editorials, commentaries, and letters to the editor. Non-peer-reviewed articles, including conference abstracts and dissertations.
Language	Studies published in English.	Studies published in languages other than English.
Publication Status	Peer-reviewed articles.	Gray literature, including reports, policy documents, and conference proceedings, unless they provide substantial and relevant data that is peer-reviewed.