The Overdose Decline and the Limits of Single-Cause Explanations

Jeffrey A. Singer

In a recent Cato blog post, I discussed several factors that may be contributing to the current and welcome drop in overdose deaths. I wrote:

“None of the most plausible explanations for the decline in overdose deaths involves intensifying the drug war. If anything, the evidence points toward lower-risk patterns of drug use, harm reduction, naloxone access, and behavioral adaptation in response to an increasingly dangerous illicit market.”

One possible contributor I did not discuss is a temporary fentanyl supply shock. In an excellent paper published earlier this year in Science, Kasey Vangelov and colleagues present evidence that disruptions in the illicit fentanyl supply may have contributed to the decline in overdose deaths that began in mid-2023. 

The Fentanyl Supply Shock Hypothesis

Vangelov et al. make an important point. Changes in fentanyl purity and availability could well be contributing to the decline in overdose deaths. However, I think the authors may place too much emphasis on Chinese precursor controls and too little on illicit drug markets’ ability to adapt to supply disruptions.

The authors point to several indicators suggesting that the illicit fentanyl market experienced a significant supply disruption beginning in mid-2023. They note declines in fentanyl purity, reductions in fentanyl seizures, and a surge in online discussions among drug users reporting fentanyl shortages. Because overdose deaths began falling around the same time in both the United States and Canada, they speculate that increased Chinese enforcement against manufacturers and exporters of fentanyl precursor chemicals may have disrupted fentanyl production throughout North America.

One would expect this to be only a temporary phenomenon, as precursor production in other countries will increase to meet demand. Vangelov et al. might be overemphasizing China’s role in supplying fentanyl precursors. As I wrote here in 2024:

“The Times reported that Trump believes China can do a better job stopping the flow of Chinese-made fentanyl precursors to the transnational drug cartels located in Mexico, where they synthesize fentanyl in underground labs. But fentanyl precursors also come from India, Myanmar, and other parts of Southeast Asia. If China cracks down on domestic precursor labs, that means increased business for dealers in those countries. Waging a war on drugs is like playing a game of whack-a-mole.”

The authors acknowledge that traffickers adapt to supply disruptions but do not consider the possibility that producers may respond by shifting to synthetic opioids that rely on different chemical pathways and precursor materials. Benzimidazole opioids such as nitazenes are already appearing with increasing frequency in toxicology reports, and other novel synthetic opioids may follow. A disruption in fentanyl production does not necessarily translate into a lasting reduction in the availability of potent synthetic opioids.

A Longer-Term Perspective

After reading my recent post on the decline in overdose deaths, Donald S. Burke, MD, Professor and Dean Emeritus of the University of Pittsburgh School of Public Health and a co-author of the landmark study showing that overdose mortality has followed a remarkably stable exponential growth trajectory since at least the late 1970s, wrote to say that he found my analysis broadly consistent with his own thinking on the subject. He also drew my attention to a forthcoming commentary that he co-authored with Hawre Jalal in the International Journal of Drug Policy, titled “Long-term Perspective on the Recent Abrupt Decline in Drug Overdose Mortality.”

The paper, currently in press, directly responds to the Vangelov analysis. Notably, Burke and Jalal do not rule out the possibility that a fentanyl supply shock contributed to the decline in overdose deaths. Rather, they argue that the supply-shock explanation captures only part of a much larger story.

Burke and Jalal argue that the recent decline should be understood in the broader context of the overdose epidemic’s long-term trajectory. In their view, overdose deaths during the COVID era were a temporary departure from that trajectory, driven by social disruption, changes in treatment access, labor-market volatility, income shocks, and other pandemic-related factors. As those forces receded, overdose mortality would be expected to return toward its historical trend. They also raise the possibility of “mortality displacement”—the idea that the pandemic accelerated overdose deaths among the most vulnerable, leaving a temporarily smaller population at highest risk. As Burke put it in his email to me, the excess overdose deaths during the pandemic may have consumed some of the “fuel for the fire.” Under that interpretation, the recent decline may reflect a correction after the pandemic-era surge rather than evidence of a lasting break from the epidemic’s underlying dynamics.

The mortality displacement hypothesis also aligns with an observation by my frequent co-author, Josh Bloom, Director of Chemical and Pharmaceutical Science at the American Council on Science and Health. Bloom has wondered whether the pandemic-era surge in overdoses substantially reduced the population of active drug users, while younger cohorts have not replenished that population at historical rates. Gen Z reports lower rates of alcohol, tobacco, and many forms of drug use than previous generations. If that demographic shift is occurring, it could help explain part of the recent decline in overdose deaths and further suggest that no single explanation fully accounts for the trend.

Vangelov and colleagues have identified a plausible factor behind the recent decline in overdose deaths. Burke and Jalal suggest that the decline may also reflect the unwinding of pandemic-era distortions and the effects of mortality displacement. They also point to a broader set of contributing factors, including wider naloxone availability, harm reduction efforts, lower-risk patterns of drug use, and behavioral adaptation to an increasingly dangerous illicit market.

The encouraging news is that overdose deaths have fallen substantially. The less encouraging news is that no one can say with confidence whether the decline will continue. If Burke and Jalal are correct, overdose mortality could eventually return to its historical trajectory. If Vangelov and colleagues are correct, illicit drug markets may adapt to current supply constraints by sourcing new precursors or shifting to other synthetic opioids.

For now, the evidence points to a more complex story than either a drug-war success narrative or any single-cause explanation can capture. The recent decline likely reflects the interaction of several forces rather than a single dominant cause. Changes in drug markets, drug-use behavior, harm reduction, treatment access, naloxone availability, and the lingering effects of the pandemic all appear to be contributing factors. Assertions that intensified drug-war enforcement deserves substantial credit for the decline remain unsupported by the available evidence.

Source: https://www.cato.org/blog/overdose-decline-limits-single-cause-explanations