Among U.S. President Donald Trump’s first actions after returning to office in January 2025 was imposing new tariffs on Canada, China, and Mexico, which he accused of sending fentanyl to the United States. The allegation against Canada was completely unfounded. China’s role in the story, however, is more complex. Beginning in 2015, the U.S. opioid overdose epidemic accelerated dramatically with the arrival of fentanyl imported at first directly from China and later manufactured in Mexico using cheap, Chinese-produced chemical precursors.

In 2000, 17,000 people in the United States died of drug overdoses, with only about 780 involving synthetic opioids such as fentanyl. Two decades later, fatal drug overdoses reached 92,000. By mid-2023, that figure had peaked at 111,000 over the previous 12 months, and 70 percent involved fentanyl. But unexpectedly, in June 2023, these gruesome numbers began to plummet. By September 2025, fatal drug overdoses over the past 12 months had fallen by almost 40 percent, to 73,000—well below the 2020 figure. The number of deaths involving fentanyl fell by nearly 50 percent. Canadian opioid overdoses declined more or less in parallel with those in the United States. 

At first, some drug-policy experts thought the shift was just a return to baseline after the COVID-19 pandemic, when fear, grief, and social isolation led to increased drug use and a spike in overdose deaths. But the decline’s timing does not match up with the waning of these stressors: the downturn began well after COVID lockdowns had ended, and deaths kept dropping for two years. In an article we published in Science with our colleagues Kasey Vangelov, Harold Pollack, and Bryce Pardo, we found that the supply of fentanyl in both the United States and Canada constricted at around the same time as the downturn in overdose deaths. Because illegal fentanyl consumed in the United States is primarily imported from Mexico, whereas fentanyl consumed in Canada is also manufactured in Canada, the timeline raises the intriguing possibility that the supply shock came from China, which provides the precursor chemicals that underpin North American fentanyl production. 

China is a source of the problem but also, potentially, of the solution. An effective crackdown by Chinese authorities on manufacturers of the critical chemicals needed to make fentanyl has the potential to reduce the U.S. fentanyl problem substantially. And if China has the power to constrain illegal drug actors, this could make fentanyl control an enduring feature of negotiations between Washington and Beijing, resulting in more collaboration—or friction, depending on whether overdoses rise or fall. Either way, to make successful policy, U.S. politicians need to get more curious about the full drug-supply chain.

The problem of illegally manufactured fentanyl is largely confined to North America. Fentanyl entered the Canadian and U.S. illegal opiate markets around 2014 because drug dealers in those two countries found it efficient to substitute cheap fentanyl for the more expensive heroin that previously dominated. Back then, there was little specific demand for fentanyl, and that demand could usually be satisfied by diverting fentanyl from the health-care system.

Initially, fentanyl was consumed mainly by heroin users, and it massively increased their death rate. The pool of potential consumers—and the number of fentanyl-related deaths—grew when dealers began marketing fentanyl via counterfeit pills, which reached populations that shunned injecting drugs. Other dealers began mixing it into methamphetamine and cocaine, many of whose consumers had not developed a tolerance to opioids. 

Just as........

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