He classified fentanyl as a “weapon of mass destruction,” saying that it was “flooding into our country.” The moves are part of Trump’s “all-out war” on drugs, which has included the capture of Venezuelan President Nicolás Maduro on narco-terrorism charges, and the bombing of boats believed to be carrying drugs. Yet there are growing indications that, even before Trump took office, the United States had turned the corner on the fentanyl crisis. The data are striking.

A recent study published in Science magazine noted that the annual rate of fentanyl overdose deaths had plunged by one-third between its peak in mid-2023 and the end of 2024. Seizures of the opioid had dropped 37 percent by that point, suggesting less was being smuggled over the border. The numbers have ticked down further since then.

Researchers and officials are still debating what caused such a sharp turnaround in the most lethal drug epidemic in U.S. history, one that’s caused more than 300,000 deaths. Teasing out the causes is complicated by the opacity of the criminal world. It appears, though, that the main factors may be more subtle than the drug busts or spectacular kingpin arrests that typically grab headlines.

The epidemic is still not over. Fentanyl remains the number one source of fatal U.S. overdoses, and traffickers continue to introduce deadly new synthetic drugs. But the turnaround in the fentanyl crisis offers some hope in the decades-long battle against drug trafficking and addiction.

Here are some theories on what happened. A massive supply shock – maybe caused by China U.S. anti-drug policy has traditionally focused heavily on reducing supply—eradicating coca and opium crops, arresting traffickers, and snagging ships and trucks transporting contraband. Many drug experts had their doubts about the long-term effectiveness of the approach.

Seizing a big drug shipment “doesn’t inflict very much pain on the bad guys,” who consider it a cost of business, said Jonathan Caulkins, a veteran drug-policy researcher at Carnegie Mellon University. “They can usually just replace it.” The illegal drug trade tends to be highly adaptable, noted Caulkins. When security forces strike at their networks, traffickers switch to new routes, identify alternative ways of making drugs or replace jailed leaders.

The business is simply too lucrative to abandon. Yet, in the past year, Caulkins has been struck by what appeared to be an important disruption of supply. In the study published in Science, he and five other U.S. researchers looked not just at data on fentanyl seizures and fatalities, but what the actual users were saying.

Examining the Reddit platform, the researchers found the number of posts complaining of fentanyl shortages rose in July 2023, spiked later that year and remained high in 2024, roughly tracking the drop in overdose deaths. There were other signs of a supply shock. The DEA reported a decline in fentanyl purity throughout 2024.

It appeared that fentanyl cooks in Mexico were finding it harder to get key ingredients for the opioid from China, the main producer of such precursor chemicals, the agency said. Mexican cartels are the main supplier of U.S. fentanyl. The U.S. researchers hypothesized that a Chinese government crackdown on precursors led to a huge fentanyl shortage.

To test that conclusion, they examined fentanyl overdose deaths in Canada. That country’s fentanyl is largely produced not by Mexican traffickers, but by domestic criminals. Therefore, “whatever we do on the southwest border will have no effect on Canada,” said a second researcher involved in the Science paper, who spoke on the condition of anonymity.

But Canada also had a notable decline in overdose deaths. What their fentanyl producers had in common with the Mexican cartels was the use of Chinese precursors. Both the first Trump administration and the administration of former U.S. president Biden, had pressured the Beijing government to attack the illegal precursor trade, leading to a formal agreement in November 2023.

Many experts initially doubted China’s ability to corral thousands of precursor producers. Now, some theorize its government may have decided that disciplining such manufacturers— a tiny part of its economy—could have outsized benefits in its relations with the United States. Still, the argument about the China connection leaves unanswered questions about precursors.

“Why the heck haven’t they [traffickers] been able to figure out another source?” Caulkins said. “That’s a puzzle.” The market for fentanyl has shrunk If a supply shock is one reason for the easing of the crisis, a drop in demand may be another. That could explain why the street price of