Out of Prescription Opioids and into Other Drugs? the Unintended Consequences of Stricter Opioid Prescribing Laws on Drug Abuse

Objective. – To determine how supply side restrictions on opioids imposed by recent State-mandated Prescription Drug Monitoring Programs (PDMPs) that require prescribers to review patient PDMP reports prior to prescribing prescription opioids, reduce opioid prescribing and related poisonings and overdose deaths. Additionally, the study seeks to identify mechanisms underlying the continued increase in prescription opioid-involved overdose deaths despite stricter monitoring of opioid prescribing by means of PDMPs.

Data. – Impact of mandatory PDMPs on the aggregate legal supply of prescription opioids is studied using the Drug Enforcement Administration’s Automation of Reports and Consolidated Orders System (ARCOS). Impact of mandatory PDMP laws on poisonings are measured using rates of poisoning exposure calls to any of the fifty-five American Association of Poison Control Centers (AAPCC) across the country between 2011-2017, recorded in the National Poison Data System (NPDS). Each confirmed poisoning call records all substances involved, cause of poisoning (intentional misuse, adverse drug reaction, unintentional therapeutic error or other), and the severity of the resulting medical outcome (minor versus severe adverse medical effect including death). Prescribing changes in response to PDMP laws for four other drug classes that are contraindicated for use with opioids – antidepressants, benzodiazepines, stimulants and muscle relaxants - are measured for the Medicaid population using the State Drug Utilization Data (SDUD).

Methods. – Exploiting cross-state variation in timing of implementation of mandatory PDMPs this study uses difference-in-difference and event-studies to evaluate the impact of these laws on the aggregate supply of prescription opioids and the incidence of all prescription opioid-involved poisonings. Impacts of the laws on the severity of poisonings (minor or severe) and incidence of multiple-substance poisonings is also explored. Finally, we investigate changes in multiple-substance, prescription opioid poisonings that also involved – illicit drugs, like heroine, benzodiazepines, antidepressants, stimulants and muscle relaxants – following mandatory PDMPs.

Results. – Mandatory PDMPs are associated to a 3 percent decline in the aggregate supply of prescription opioids but no decline in the rate of all prescription opioid-involved poisoning calls recorded in the NPDS. Distinguishing by the intensity of poisoning, we find that a third of the calls that resulted in severe adverse medical outcome, including death, in fact increased by 10 percent. This increase is driven by an 11 percent increase in the incidence of prescription opioid poisonings that also involved benzodiazepines and antidepressants. Moreover, self-reported intentional misuse/ suicide, rather than adverse drug interactions, therapeutic errors or other causes, underlies the increase. We also find weak evidence of increased supplementation of prescription opioids with illicit drugs that result in more severe poisonings with worse medical outcomes, including death.

Conclusions. – This study finds that mandatory PDMP laws are associated with measurable decline in prescription opioid supply. However, an unintended consequence of these laws is a significant increase in rates of severe poisonings, resulting from intentional supplementation of prescription opioids with less monitored prescription drug classes that are contraindicated for concurrent-use – benzodiazepines and antidepressants - and, to a smaller extent, with illicit drugs, for purposes of misuse.