When overdose rates spiked in Oregon in 2021, blame quickly turned to a new state law that had recently decriminalized low-level drug possession.

But a recent study implicates another factor: the introduction of fentanyl into Oregon’s unregulated drug market.

The analysis “follows the path of fentanyl across the country and offers testament to the destruction wreaked by this highly potent drug,” says study author Brandon del Pozo, PhD, an assistant professor of medicine and of health services, policy, and practice (research). “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.”

Oregon was the first state to decriminalize small amounts of any drug for personal use. Last April, in reaction to the state’s skyrocketing overdose rate and other concerns, the governor rolled back that law, making “personal use possession” a misdemeanor punishable by up to six months in jail.

In the paper, published in JAMA Network Open, del Pozo and colleagues reported 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,” he says.

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. The decriminalization law took effect that February.

“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 says.

He and his coauthors determined that the decriminalization law was not associated with the state’s increase in fatal drug overdose rates in the two years after its enactment. Furthermore, they wrote, “Recriminalization in Oregon may not reduce the rate of overdoses observed in a state saturated with fentanyl.”

Del Pozo adds, “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.”