Experts voiced approval of a new agreement between the United States and China that aims to control fentanyl smuggling into the U.S. black market, but they warned against expecting a quick impact on the drug’s skyrocketing death toll.

President Trump said Sunday evening that Beijing has agreed to treat the powerful opioid and its many analogues as controlled substances, a decision the White House said would subject the country’s illegal fentanyl dealers “to China’s maximum penalty under the law.”

That is certainly a positive step, said academic and law enforcement authorities who track the problem. But left unclear — in part because the White House offered few details — is exactly how China plans to curb the extremely powerful drug that now dominates illegal opioid traffic in the United States.

“I think it’s a very good thing,” said Vanda Felbab-Brown an expert on illicit economies at the Brookings Institution. “However, I wouldn’t hold my breath on how big that impact will be.”

Trump and some U.S. politicians are describing the deal in sweeping terms, issuing statements that China plans to completely control the substance, said Bryce Pardo, an associate policy researcher at the Rand Corp. The Chinese, by contrast, have said they’re going to enforce existing regulations. Both appear to be playing to powerful domestic interests.

“Within that, there might be some middle ground,” Pardo said.

In a statement Monday, Kirsten Madison, assistant secretary for the State Department’s Bureau of International Narcotics and Law Enforcement Affairs, said China’s “commitment to schedule all fentanyl-related substances as a class is a major milestone, with the potential to greatly advance U.S.-China cooperation to stem the flow of deadly synthetic opioids into our nation . . . We welcome this move and look forward to seeing the Chinese government implement and enforce these controls as soon as possible.”

According to data released last week by the Centers for Disease Control and Prevention, fentanyl and its synthetic cousins caused 28,466 fatal overdoses in 2017, about 60 percent of the 47,600 U.S. opioid overdose deaths.

That was a 47 percent increase from 2016 and nearly triple the number of fentanyl-related deaths recorded in 2015. Provisional numbers for the first four months of 2018 indicate a possible plateau in overdose deaths from all drugs, but it is too early to rely on that data, experts said.

The United States and China have worked toward cooperation on stemming the flow of illegal fentanyl since the Obama administration, with modest steps taken along the way.

In August, as Congress was considering legislation to curb fentanyl smuggling through the mail, Trump tweeted that China’s illicit fentanyl fuels the U.S. opioid epidemic.

“It is outrageous that Poisonous Synthetic Heroin Fentanyl comes pouring into the U.S. Postal System from China. We can, and must, END THIS NOW!” the president tweeted. China rejected the assertion. The legislation ultimately was approved and Trump signed it into law.

Pharmaceutical fentanyl, for which precursor chemicals are imported mainly from China, is a legal synthesized drug used for the intense pain of end-stage cancer and for surgery. Illegal fentanyl is also synthesized chemically, and may have hundreds of analogues — versions that differ very slightly from the original to avoid running afoul of laws.

That’s why a crackdown or ban on the entire class could help the abuse crisis significantly.

The primary complication for any effort in China, several experts said, is that chemicals for legal fentanyl are produced in hundreds, perhaps thousands, of legitimate pharmaceutical plants and imported to the United States by drug companies. Rooting out illegal clandestine labs is much easier than finding diversion by rogue operators in approved facilities, they said.

In China, as in the United States, pharmaceutical companies wield enormous power, even if Beijing’s authoritarian government could crack down heavily if it chooses to. The industry generates revenue and jobs that are an important part of the Chinese economy.

“For them to shut down an entire legal pharmaceutical company comes with many, many problems,” said Felbab-Brown, the Brookings researcher.

Yet many who follow the issue were encouraged that Washington and Beijing managed to reach any agreement on the issue as the two countries spar over tariffs and trade.

“This is a very welcome announcement during this so-called trade war, that we can still focus on things that are meaningful in other ways,” said Daniel Ciccarone, a professor at the University of California at San Francisco. “We don’t have to hold this hostage.”

Kathleen J. Frydl, a historian and author of “The Drug Wars in America, 1940-1973,” said the Trump administration might have used the trade conflict to pressure Chinese President Xi Jinping.

“The Trump administration has chosen to wield the powerful and effective tool of trade sanctions to cajole China into curbing fentanyl production and export,” Frydl said. “Unfortunately, they have settled for China’s prohibition of fentanyl as an appropriate concession, taking cues from a conventional drug war playbook that has proven ineffective elsewhere. Hopefully there is an undisclosed agreement monitoring the export of fentanyl, especially to Mexican drug traffickers, or one that pertains to China’s largely unregulated chemical manufacture industry — otherwise prohibition will amount to little.”

Tom Synan, the chief of police in Newtown, Ohio, was hopeful that cooperation with China could help ease the burden on local governments, which have been left to deal with the drug crisis by arming first responders with the fast-acting overdose antidote naloxone.

“If we can transition from this to start treating addiction, it will help the systems recover,” Synan said. “They won’t be overwhelmed and it will save money and lives.”

But others feared that success in China could just move the fentanyl production problem to India, which also has a large pharmaceutical manufacturing sector, or to Mexico, where cartels smuggle the drug into the United States along with heroin. An illicit Indian fentanyl lab was shut down earlier this year, said Pardo, the Rand researcher.

“Say China does get its regulatory house in order and they are able to shut down these manufacturers, he said. “We still have a demand here at home, and it is entirely possible that . . . the problem could move to that country.”