Did the illicit fentanyl trade experience a supply shock?

Fatal overdoses from synthetic opioids, most notably fentanyl, steadily increased more than 25-fold in the United States over 15 years, peaking at 76,000 in 2023 (1). This trend began to sharply reverse in mid-2023, dropping the annual rate of fentanyl overdose deaths (ODDs) by over a third by the end of 2024 (1). Explaining this unexpected drop is of major scientific and policy interest. Whether a supply shock could account for a substantial part of the decline is challenging to determine because drug trafficking organizations operate in secret. Synthesizing data from the US and Canadian governments and from discussions on the social media platform Reddit, we suggest there was a major disruption in the illicit fentanyl trade, possibly tied to Chinese government actions, that translated into sharp reductions in overdose mortality beginning in mid- or late-2023 and continued into 2024 across both the US and Canada.