OBJECTIVE: To determine the budget impact of implementing multidisciplinary complex pain clinics (MCPCs) for Veterans Health Administration (VA) patients living with complex chronic pain and substance use disorder comorbidities who are on risky opioid regimens. DATA SOURCES AND STUDY SETTING: We measured implementation costs for three MCPCs over 2 years using micro-costing methods. Intervention and downstream costs were obtained from the VA Managerial Cost Accounting System from 2 years prior to 2 years after opening of MCPCs. STUDY DESIGN: Staff at the three VA sites implementing MCPCs were supported by Implementation Facilitation. The intervention cohort was patients at MCPC sites who received treatment based on their history of chronic pain and risky opioid use. Intervention costs and downstream costs were estimated with a quasi-experimental study design using a propensity score-weighted difference-in-difference approach. The healthcare utilization costs of treated patients were compared with a control group having clinically similar characteristics and undergoing the standard route of care at neighboring VA medical centers. Cancer and hospice patients were excluded. DATA COLLECTION/EXTRACTION METHODS: Activity-based costing data acquired from MCPC sites were used to estimate implementation costs. Intervention and downstream costs were extracted from VA administrative data. PRINCIPAL FINDINGS: Average Implementation Facilitation costs ranged from $380 to $640 per month for each site. Upon opening of three MCPCs, average intervention costs per patient were significantly higher than the control group at two intervention sites. Downstream costs were significantly higher at only one of three intervention sites. Site-level differences were due to variation in inpatient costs, with some confounding likely due to the COVID-19 pandemic. This evidence suggests that necessary start-up investments are required to initiate MCPCs, with allocations of funds needed for implementation, intervention, and downstream costs. CONCLUSIONS: Incorporating implementation, intervention, and downstream costs in this evaluation provides a thorough budget impact analysis, which decision-makers may use when considering whether to expand effective programming.