<p>Substance use disorders (SUDs) represent a critical public health challenge, frequently compounded by co-occurring mental health conditions. While integrated care is the evidence-based standard of care, implementation gaps persist. This study utilized data from 3764 outpatient facilities from the 2023 National Substance Use and Mental Health Services Survey to evaluate mental health service integration and identify key predictors. Despite treating highly comorbid populations, 33% of facilities offered no mental health assessments. Integration levels varied sharply by facility type; opioid treatment programs (OTPs) served more clients with co-occurring disorders and were over twice as likely to provide comprehensive integration (43%) compared to non-OTPs (20%). Generalized ordered logistic regression revealed that private non-profit and public ownership, Joint Commission (TJC) accreditation, private insurance acceptance, and a higher co-occurring client volume were strong positive predictors of integrated care in the full sample. Conversely, CARF accreditation, Medicaid acceptance, and being in the Midwest were associated with a lower likelihood of integrated care. Stratified analysis uncovered critical variations by program type. Medicaid acceptance specifically lowered odds of integration in OTP. Furthermore, CARF accreditation was a negative predictor for OTPs but a positive predictor for non-OTPs. At the state level, location in a Medicaid managed care organization state significantly reduced integration odds solely for OTPs, while an increasing proportion of adults with a drug use disorder significantly increased likelihood of integration for non-OTPs. These results underscore how organizational structures, including facility type, accreditation, and state-level funding mechanisms shape care delivery. Addressing these systemic barriers, particularly financial and regulatory, is essential to closing the implementation gap and ensuring comprehensive care.</p>