PROVIDENCE, R.I. [Brown University] — When overdose rates spiked in Oregon in 2021 after the state decriminalized low-level drug possession, blame quickly turned to the new state law. But a new study by researchers at the Brown University School of Public Health implicates another factor: the introduction of fentanyl into Oregon’s unregulated drug market.

“What's compelling about this analysis is that it follows the path of fentanyl across the country and offers testament to the destruction wreaked by this highly potent drug,” said study author Brandon del Pozo, an assistant professor of medicine (research) and health services, policy and practice (research) at Brown. “When fentanyl arrives in Oregon in early 2021, we can see from the data that it wreaks destruction there, too. That was also when decriminalization was taking effect in Oregon.”

With the implementation of Measure 110 in 2021, Oregon became the first U.S. state to decriminalize small amounts of any drug for personal use. In April 2024, in reaction to the state’s skyrocketing overdose rate and other concerns, Oregon’s governor signed into law a bill that rolled back Measure 110 by making “personal use possession” a misdemeanor punishable by up to six months in jail.

Del Pozo said that there hasn’t been an analysis of the association of Measure 110 with overdose mortality that has fully accounted for the introduction of fentanyl to Oregon’s unregulated drug market, despite the fact that fentanyl is known to be the prime driver of fatal overdose in the U.S.

In the paper, published in JAMA Network Open, del Pozo and his team evaluated the association between changes in state fatal drug overdose rates and the escalation of fentanyl availability across the country from 2008 to 2022.

Comparing Oregon to 48 U.S. states as well as Washington, D.C., that did not decriminalize drug use, they analyzed national data from state drug laboratories showing what kinds of illicit drugs were being recovered and tested. They focused on the percentage of the drug supply accounted for by fentanyl and its analogs, which increased state by state over time. The researchers then plotted this data against publicly available information from the U.S. Centers for Disease Control of each state’s fatal drug overdoses.

They found that across all states, an increase of fentanyl in the illicit drug supply was strongly correlated with an increase in drug overdose fatalities.

“It was a very tight relationship: the more fentanyl that was recovered and tested by the state, the higher the fatal overdose rate in that state,” del Pozo said.

The researchers determined the inflection point when each state experienced a rapid escalation of fentanyl in its unregulated drug market, making it the dominant illicit opioid in that state. For Oregon, that change took place in the first half of 2021. M110 took effect in February 2021.

“It was very unfortunate timing, because it means the effects of decriminalization were confounded by an event — fentanyl supply shock — that dramatically drives up fatal overdose, state by state, as it occurs,” del Pozo said.

The researchers used the data to construct a model that determined the decriminalization of drug possession in Oregon was not associated with an increase in fatal drug overdose rates in the two years after its enactment. They concluded that when evaluating the effect of public policies on overdose mortality, it is critical to account for the role of fentanyl as the principal driver of the nation’s overdose mortality epidemic.

“If we’re not modeling fentanyl’s effects on a community when we’re talking about strategies to address the overdose crisis, then we’re not following the evidence,” del Pozo said.

The change in Oregon’s drug policies that reversed Measure 110 and recriminalized drug possession took place on Sept. 1, 2024.

The study reported in this press release was funded by the National Institute on Drug Abuse, part of the National Institutes of Health, with additional support from NIH’s National Institute of General Medical Sciences, under award numbers K01DA056654 and P20GM125507.