Background: Methadone maintenance therapy (MMT) is an established form of substitution therapy for opioid use disorder. Various MMT treatment models have emerged but differences in the clients they service have not been examined extensively. The current study assessed client characteristics in three MMT treatment delivery models: (1) comprehensive programs which combine methadone treatment with mandatory physician appointments and counseling, (2) low-threshold-high- tolerance (LTHT) programs which have more lenient policies and offer primary healthcare services, and (3) fee-for-service methadone programs which are run by community pharmacies and where the dispensation of methadone is the core component. Methods: Seventy participants were recruited from five treatment sites in a midsized Atlantic Canadian city and grouped based on model of care: Comprehensive program (n = 21), LTHT program (n = 26), and fee-for-service program (n = 23). Self-report questionnaires were used to collect data on demographics and substance use patterns. Results: Results indicated that participants in the fee-for-service group reported higher levels of substance use severity and polysubstance use than participants in the comprehensive and LTHT groups. Conclusion: The findings of this research have important implications for the implementation of fee-for-service methadone programs.