Beijing -- China said Monday it would soon begin regulating all fentanyl-related drugs as a class of controlled substances. The change has long been pushed for by U.S. officials, including President Trump, as a way to stem the flow of lethal opioids from China.

The sweeping change in the way China regulates drugs that mimic fentanyl takes effect May 1 and could help end the game of regulatory whack-a-mole with chemists who can manufacture novel opioids faster than they can be banned. It could also facilitate prosecutions of opioid merchants in China, who until now have skirted the law by manufacturing and exporting fentanyl variants that were technically legal in China.

"We firmly believe that listing the entire class of fentanyl substances will completely block the loopholes that enable law breakers to evade punishment by simply modifying one or several atoms, functional groups or other groups," said Liu Yuejin, vice-commissioner of China's National Narcotics Control Commission. "It will effectively prevent the massive abuse of fentanyl substances and illegal drug trafficking and smuggling activities, and contribute to global drug control with China's wisdom and power."

Monday's announcement from China's Ministry of Public Security, National Health Commission and National Medical Products Administration makes good on a pledge Chinese President Xi Jinping made to Mr. Trump during the G-20 summit in Argentina late last year.

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At the time, Mr. Trump said China's new regulations could be "a game changer" for the United States, where tens of thousands of people die annually from opioid overdoses.

China already controls 25 variants of fentanyl, plus two precursors used to make the drug. Data from the U.S. Drug Enforcement Administration have shown that when China bans a variant of fentanyl, seizures of that analog in the U.S. fall.

U.S. officials have repeatedly pointed to China as the main source of synthetic opioids shipped into the country directly by mail or transported via Mexico. China on Monday again denied that claim.

"China's control over fentanyl drugs is very strict," Liu told reporters. "It cannot be the main source for the United States. The U.S. accusation lacks evidence and is contrary to the facts."

What is fentanyl?

Fentanyl is a synthetic opioid that is 80 to 100 times stronger than heroin or cocaine, according to the U.S. Drug Enforcement Agency (DEA). It was first developed to relieve pain in cancer patients, but has become a primary culprit in U.S. drug overdose deaths.

Fatal drug overdoses peaked in 2018, and according to preliminary data from the Centers for Disease Control and Prevention, the number of deaths from overdoses involving fentanyl was more than 11 times higher in 2016 than in 2011.