When things go wrong, those in power often promise to make it right. But do they? In this series, The Times investigates to see if those promises were kept.

XINGTAI, China — An online pharmacy advertising itself as a seller of “high purity, real pure” fentanyl still responds right away to potential customers.

“Which products do you want to buy,” a salesperson replied within a minute to an inquiry in English on WhatsApp, the encrypted messaging service.

But when contacted from an American telephone number and asked about the availability of fentanyl, the synthetic opioid fueling an epidemic killing tens of thousands of Americans a year, the seller demurred.

“I don’t sell any more.”

Until recently, much of the illicit fentanyl that found its way to the United States came like this: easily ordered online from a source in China and seamlessly shipped by international delivery companies, including the United States Postal Service.

Fentanyl sourced from China accounted for 97 percent of the drug seized from international mail services by United States law enforcement in both the 2016 and 2017 fiscal years, according to the Drug Enforcement Administration.

Now, China’s Communist government is taking steps to stop the flood, as the country’s leader, Xi Jinping, promised President Trump he would do.

After the two leaders met in Buenos Aires at the Group of 20 summit at the end of last year, the White House released a statement saying that “President Xi, in a wonderful humanitarian gesture, has agreed to designate fentanyl as a controlled substance.”

What We Found

‘Stricter and stricter’ control

Some six months later, China did exactly that. As a result, the large, freewheeling and mostly unregulated fentanyl industry that had operated in a gray area of Chinese law appears to have stopped selling the drug for export — or at least as openly as hundreds of suppliers once did.

Some of the distributors, who still can be easily found in online searches, claimed to be complying with the new rules banning the overseas sale of synthetic opioids.

Others appeared to have shut down their operations, disconnecting numbers which had previously reached salespeople offering to mail the drugs to the United States — no questions asked.

China’s new focus on shutting down the trade has meant shipments of fentanyl to the United States have declined significantly in the last year, according to Chinese officials, citing figures from the United States Customs and Border Protection agency. The American agency did not dispute that drop.

“China’s control over fentanyl substances is becoming stricter and stricter,” said Yu Haibin, the deputy director of the country’s National Narcotics Control Commission.

Following a tightening of drug controls that took effect May 1, the government put 91 manufacturers and 234 individual distributors under “strict supervision,” warning them not to export fentanyl or related drugs, like carfentanil, according to a government report released in September. It claimed to have increased inspections and arrests in 13 cities and regions where pharmaceutical companies have proliferated.

One of them is Xingtai, an industrial city about 250 miles south of Beijing, where a court earlier this month convicted nine people of smuggling fentanyl into the United States. The convictions capped an investigation that began in 2017 with a tip from American drug-enforcement agents. The accused ringleader received a suspended death sentence; two others were sentenced to life in prison.

The case was one of three investigations in which the Chinese authorities have been cooperating with American law enforcement, Chinese officials said. The investigations have come after a torrent of criticism that Chinese officials were lax toward — or even complicit in — a major supply chain fueling the fentanyl crisis in America.

China’s harshest critics have even accused the country of deliberately flooding the market as revenge for the Opium Wars of the 19th century, though there is no evidence of that.

As recently as August, Mr. Trump had chastised the Chinese leader on Twitter for not keeping his promises to get tough on fentanyl. The White House Office of National Drug Control Policy called the recent convictions “a positive step.”

Experts and officials in the United States warned, however, that it was far too soon to declare a victory in China’s fight against fentanyl.

The market for the drug — which the Chinese like to point out has always been largely American — appears insatiable. For a sense of how the crisis has exploded: In the 2019 fiscal year that ended in October, American customs agents seized 1,154 kilograms of fentanyl, or 2,545 pounds, compared with 31 kilograms, or 70 pounds, in 2015.

Fentanyl is cheap, easily synthesized in a lab and more addictive than heroin. That means the financial rewards will remain high enough to entice those willing to break the law, especially in a large and poorly regulated chemical industry like China’s.

So manufacturers and distributors that had operated in the open may simply shift their operations underground.

“The scale of China’s under-regulated industries allows for minimally trained technicians with access to the proper inputs to follow simple synthesis steps while avoiding oversight,” the authors of a new report on fentanyl by the RAND Corporation wrote. “China’s pharmaceutical and industrial chemical industries are large and beyond the reach of U.S. law enforcement.”

What We Found

Plugging legal holes

Even so, the steps China has taken to reduce the flow of fentanyl are real, according to experts and officials on both sides of the Pacific.

China has some of the strictest drug laws in the world, allowing capital punishment against major producers and traffickers. Until recently, however, loopholes in legislation and enforcement allowed the production of synthetic opioids like fentanyl to skirt the attention of the authorities.

In China, as in the United States, fentanyl can be legally prescribed and is used as an anesthetic in surgery and for severe pain relief. Because of its potency, its production is strictly controlled by law.

Until this year, however, China’s laws did not cover new, chemical variants of fentanyl that were constantly being produced to sidestep existing legal restrictions. Manufacturers could simply adjust the chemical structure slightly and create a new analogue of the drug, not yet banned. In this gray area of the law, production in China soared.

“It’s just like water: They’re finding the gaps and the cracks,” Bryce Pardo, an associate policy researcher at the RAND Corporation and a lead author on the organization’s report, said in an interview.

In April, the Chinese government moved to plug those legal holes. It announced it would place all variants of fentanyl — as a class — on the list of controlled substances, rather than individually adding each new version of the drug to the banned list after it had hit the streets. With the export controls that are applied to drugs on the list, the fentanyl variants that had fallen into the legal gray area before were now explicitly banned from being sold abroad.

Tang Jianbin, a lawyer in Beijing who specializes in criminal drug cases, said the move was a significant concession to American demands. The country even had to pass a new law allowing it to designate the entire class of synthetic opioids as controlled substances.

“This legal adjustment is an innovation in our country,” Mr. Tang said.

China made this move in the middle of its protracted trade war with the United States, and it may have been done to help resolve the acrimonious — and continuing — dispute.

Drugs entering China from the West have a dark historical resonance in the country, which is still bitter over the forced importation of opium by the British in the 19th century, the cause of two wars and the ceding of Hong Kong.

And Chinese officials have long bristled at any criticism they were negligent on the law enforcement front and were always quick to point out that fentanyl was a uniquely American problem. Opioid use — and abuse — is far higher in the United States than anywhere else in the world, and there are plenty of other sources of the drug beyond China.

Mr. Yu, the narcotics agency deputy director, cited statistics from the United States Customs and Border Protection showing that of the 536.8 kilograms of fentanyl seized between October 2018 and March 2019, only 5.87 kilograms, or just over 1 percent, was shipped from China.

“From these statistics it is clear that China is not the main source of fentanyl substances in the United States,” Mr. Yu said at a news conference in Xingtai following the verdict against the nine fentanyl dealers.

What We Found

Shipments decline, but problems endure

American officials acknowledge a decline in shipments from China, but like Mr. Trump, keep pressing the country to do more.

“While it appears that the direct shipment of fentanyl-related substances from China to the United States has declined in recent months, this is only one of many measures that the United States looks to for indicators of progress,” the customs bureau wrote in a statement responding to questions about the Chinese claims. “The most important measure of progress is the reduction of American lives lost to these drugs.”

One area where American officials would like to see more action is in pursuing manufacturers and distributors that detectives and prosecutors have linked directly to overdoses in the United States, often after painstaking investigations tracing the trail of fentanyl to its origin.

In 2018, the Justice Department announced an indictment of a father and son, Zheng Guanghua and Zheng Fujing, who had operated a company called Qinsheng Pharmaceutical in Shanghai.

The company appears to have closed — or gone underground — but the two men are believed to be at large.

It was not clear if the American case against them was one of the other two cases where officials said Chinese and American investigators are cooperating. Mr. Yu, when asked, declined to discuss those cases.

There is still plenty of fentanyl in the United States that was shipped from China before the new law took effect.

This summer, the authorities in Virginia seized 30 kilograms of fentanyl, enough “to kill over 14 million people,” said G. Zachary Terwilliger, the United States attorney for the Eastern District of Virginia. The fentanyl was ordered from a vendor in Shanghai in April of last year.

While China’s crackdown has put significant restraints on what had been an unbridled export environment, the murky and still under-regulated nature of the chemical industry makes it difficult to shut down illicit production entirely without a more sustained effort by the Chinese authorities, according to Mr. Pardo of the RAND Corporation.

“They’re not doing everything they can,” he said, “but they’re making an effort on some level.”

The Takeaway: A promise kept, but a devastating drug problem persists.

Claire Fu contributed research from Xingtai, Ailin Tang from Shanghai and Elsie Chen from Beijing. Emmett Lindner contributed reporting from New York.