Medication-assisted treatment (MAT), in combination with counseling, is an evidence-based treatment for individuals with opioid or alcohol use disorders entering a correctional facility. Effective MAT programs maintain individuals on the medication they are prescribed when they enter the facility and also initiate MAT at entry when clinically appropriate. Providing MAT in correctional facilities is associated with multiple positive outcomes, including less risk of overdose death when reentering the community, reduced illicit drug use, lower rates of criminal activity, and increased treatment engagement during and after custody.