A recent scientific study identified the reduced supply of fentanyl as one of the primary factors behind a significant drop in the number of overdose deaths since the latter half of 2023.

There were roughly 76,000 fatal overdoses from synthetic opioids, which include fentanyl, in 2023, according to the research published last week in the journal Science. That total increased more than 25-fold over the 15 years before that, but then it “began to sharply reverse in mid-2023, dropping the annual rate of fentanyl overdose deaths by over a third by the end of 2024,” according to the research.

Around the same time, Canada also experienced a drop in the number of fatal fentanyl overdoses, which is notable because much of the fentanyl used there is synthesized domestically, unlike in the United States. Mexican drug cartels are responsible for manufacturing most of the fentanyl that enters the U.S.

But, both the producers in Canada and Mexico get the precursor chemicals needed to manufacture fentanyl from China, which has publicly agreed to work with the U.S. to stop it.

“Overall, the fentanyl killing Americans is produced in Mexico and the fentanyl killing Canadians is produced in Canada. And so where is the commonality? The commonality is back in China. So one story is something happened in China, whether it was official action or otherwise that caused reductions in supply in both places,” Dr. Jonathan Caulkins, one of the authors of the paper, told the Washington Examiner.

The U.S. and China have worked together to reduce the availability of fentanyl precursor chemicals in recent years, which represents one of the few areas of cooperation between the two powers. In November 2025, the Chinese government announced that it would begin requiring licenses for the exportation of the precursor chemicals that can be turned into fentanyl for shipment to North America.

The report noted that while their data suggests China’s actions are “one plausible explanation,” they “recognize that drawing inferences about Chinese government policy is inherently speculative given its lack of transparency.”

Another notable trend the researchers noted is that the purity of the fentanyl decreased substantially around the time of the drop in fatal overdoses. By the end of 2024, the powder purity had fallen by about 50% from where it was in May 2023, and it was roughly the same for the number of fatal overdoses.

How the purity level of fentanyl power and pills have changed before and after May 2023, when overdose deaths peaked in the United States.

Fentanyl is such a potent opioid that it has to be diluted; otherwise, it’d be too difficult not to overdose.

“Pure fentanyl would be ridiculously dangerous, and the reason is if the powder were actually pure, the amount of material that you would want to ingest is so tiny, it would be mechanically quite difficult to only take the correct amount,” added Caulkins, who is also a drug policy researcher at Carnegie Mellon University. “With fentanyl, you absolutely need to have it diluted to make it at all plausible to take it without killing people.”

The 2025 National Drug Threat Assessment, which is issued by the Drug Enforcement Agency, also found that fentanyl purity declined through 2024 and cited “indicators” that many of the Mexican drug cartels that produce the synthetic drug “are having difficult obtaining some key precursor chemicals” due to the DEA’s belief that “some China-based chemical suppliers are ware of supplying controlled precursors to its international customers.”

The report also noted that U.S. law enforcement officials seized more than 50,000 pounds of fentanyl in 2024, which represented the first time since at least 2019 that the total did not increase year-over-year.

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The drop in deaths also coincided with a surge in mentions on the media platform Reddit of a fentanyl “drought,” according to the study. There was a roughly 1,400% increase in the proportion of the number of fentanyl-related Reddit posts that mentioned a shortage or drought by the end of 2023, compared to before May of that year, when the drop in fatal overdoses began.

President Donald Trump signed an executive order declaring fentanyl a weapon of mass destruction last month, which directed Attorney General Pam Bondi to pursue criminal charges, sentencing enhancements, and sentencing variances in fentanyl trafficking cases, and called on Secretary of State Marco Rubio and Treasury Secretary Scott Bessent to take actions against financial institutions involved in manufacturing or distributing the illegal sale of fentanyl.