Abstract
State regulations governing opioid treatment programs (OTPs) vary widely in their restrictiveness, but how they affect geographic access to methadone maintenance treatment for opioid use disorder remains poorly understood. In this study of comprehensive data on methadone shipments to OTPs in 2019, we found that ZIP codes just across the border in states with low restrictiveness in OTP regulations had more than twice the OTP density and methadone shipments compared with nearby and otherwise similar ZIP codes in states with high restrictiveness. These findings suggest that restrictive state OTP regulations constrain geographic access to methadone maintenance treatment and that easing such restrictions is a viable strategy to expand access.