Policy-Induced Substitution to Illicit Drugs and Implications for Law Enforcement Activity

US states have implemented many policies to lessen the severity of the opioid crisis. This study investigates prescription drug monitoring programs, the reformulation of OxyContin, and Pill Mill laws on illicit drug possession and sellers. I perform difference-in-differences analyses to study policy-induced substitution to heroin and illicit opioids as measured through rates of heroin and diverted opioid possession and dealers. I find evidence that state policies cause increases in heroin possession and dealers, and that these effects are similar in magnitude to effects spurred by the reformulation of OxyContin.