Mr. Trump, who has accused China of being the main source of the “flood of cheap and deadly fentanyl” into America, has pledged to raise the issue as a top priority when he meets Mr. Xi for talks on Thursday. In a news conference last week, Wei Xiaojun, a senior Chinese official, disputed Mr. Trump’s assertion, saying there was no evidence for it.
Fentanyl is a synthetic painkiller that is 30 to 50 times as powerful as heroin. It is becoming more popular among users because of its potency — it takes less than a milligram for a single use — and relatively cheap cost. Drug investigators say a worrying trend is the mixing of fentanyl with heroin or oxycodone, another popular painkiller, or counterfeit prescription pills — all sold to unwitting users.
The ease of buying opioids from China illustrates how difficult it will be for the United States to win the war on the worst drug epidemic in American history. While China has pledged to cooperate with the United States to stop the flow of opioids, experts say it will be tough because of the country’s lax regulation of chemical companies, a sprawling industry of more than 30,000 businesses that face few requirements for transparency.
“The challenge is that when the chemical industry is so big like it is in China, policing it is incredibly difficult,” said Jeremy Douglas, the regional representative of the United Nations Office on Drugs and Crime for Southeast Asia and the Pacific.
“Regulating it — I wouldn’t say it’s impossible — but it is no small task.”
Analysts say Chinese chemical makers have exploited weak regulation to make the nation the world’s top producer of fentanyl. Mr. Trump has said fentanyl from China is “either shipped into the United States or smuggled across the southern border by drug traffickers.” The Drug Enforcement Administration said stopping the flow was a top priority.
Kai Pflug, a management consultant in the Chinese chemical industry, said that producers of fentanyl were able to avoid detection in part because they labeled their products as industrial rather than pharmaceutical, subjecting them to less stringent regulation.
“As long as, in China, you can produce chemicals without serious supervision,” Mr. Pflug said, “the problem will persist.”
Chinese regulators say they struggle with the speed at which chemists are able to produce new variations on fentanyl, circumventing the government’s ban on 23 fentanyl analogues.
China takes a hard-line stance on drugs domestically, executing drug traffickers and policing consumption. History textbooks and television shows widely depict how the country was ravaged by opium addiction in the 19th century, a major driver in the Opium Wars.
According to the Brookings Institution, Chinese users’ drugs of choice are ketamine, an anesthetic, or methamphetamine, a stimulant. Despite the lack of a domestic fentanyl abuse problem, Beijing said its list of banned fentanyl analogues was longer than that of the United Nations’ antidrug agency. Officials say this is a sign of the government’s willingness to assist the United States.
Beijing has not always been so helpful. Jorge Guajardo, a former Mexican ambassador to China, said he and other top Mexican officials repeatedly lobbied Chinese officials to stop the export of fentanyl precursors to Mexico.
“They always said: ‘It’s a problem for Mexico to deal with. It’s a problem with your customs. There’s nothing we can do,’” said Mr. Guajardo, who was ambassador from 2007 to 2013. “When the U.S. takes it up, it very quickly becomes their problem, because the U.S. has many other ways of retaliating.”
Mr. Trump has declared the opioid crisis a public health emergency after drug overdoses — mostly caused by fentanyl and its analogues — resulted in more than 64,000 deaths, including that of the music star Prince, in the United States last year.
Mr. Douglas of the United Nations said the Chinese authorities were moving quickly to cooperate. “They are working closely with us; they are working with the U.S. and Canada,” he said. “Obviously there is frustration because there’s a lot of political pressure in the U.S. and Canada right now to take action on this.”
In a sign that the United States was taking its fight against opioids globally, the Department of Justice last month announced indictments against two Chinese men it accused of being major fentanyl traffickers. The department said the men were responsible for the deaths of several opioid users in America.
At last week’s news conference, Mr. Wei, of the Ministry of Public Security, criticized the public announcement, saying it would hinder the case that both Beijing and Washington were working on. When asked whether China would help the United States in the extradition of the men, Mr. Wei was noncommittal, saying it depended in part on the evidence it received from America, which has no extradition treaty with China.
In China, fentanyl makers are constantly finding new ways to evade detection. A sales agent from Shanghai Changhong Chemical Technology asked for payment by Bitcoin or a money transfer that allows the recipient to be anonymous. A sales representative from Cinri Biological Technology, a company based in the central city of Wuhan, promised to conceal the fentanyl in cat food packets — and to resend any seized deliveries.
One Changhong agent acknowledged a Chinese ban on shipping U-47700 and other products but said it could still deliver via EMS, China’s state-owned express mail provider. EMS did not immediately respond to a request for comment.
Both Cinri and Changhong declined to provide phone numbers. When asked for comment, the Cinri representative responded over Skype text with the Russian word for imbecile and went silent. The Changhong representative did not respond to a request for comment.
Many Chinese chemical companies scoff at Mr. Trump’s calls for greater regulation, saying that they already face onerous demands from the Chinese government and that they are only serving customers.
Producers of fentanyl in China say they manufacture the chemical for legitimate purposes such as making painkillers for cancer patients.
“What role do we have in creating this problem?” said Cindy Wang, a saleswoman for a chemical company in Wuhan, which has sold fentanyl legitimately in the past. She spoke on condition that her firm not be identified. “It is up to the American people to deal with this issue.”