The fight against fentanyl, a synthetic opioid, is at the heart of America and China's uneasy trade-war truce.
The drug has killed more than 300,000 Americans since 2020 and related overdoses are the leading cause of death for Americans aged 18-44.
Shortly after starting his second term in office,
President Donald Trump slapped a 20% tariff on Chinese goods for the country's role in manufacturing the drug.
But last month, as part of a wide-ranging deal with his Chinese counterpart, Xi Jinping, he agreed to halve the tariff.
Mr Xi "is going to work very hard to stop the death", Mr Trump told journalists.
China has promised "significant" measures, according to the White House.
China has offered tough action before.
But this time momentum seems greater and the stakes higher.
Admittedly a recent visit to Beijing by Kash Patel, the director of the Federal Bureau of Investigation, appeared grim at points.
On the evening of November 8th the MAGA die-hard was slumped unceremoniously in a drab hotel lobby.
Yet meetings proved productive.
On November 10th officials from China's powerful public-security ministry, among other agencies,
released a list of 13 chemical "precursors" (used to make fentanyl)
which will require extra approvals before they can be sold to customers in America, Canada and Mexico.
The same day China's counter-narcotics authority issued a notice "reminding" exporters of the "legal risks"
involved with selling precursors and drug-making equipment to the three countries.
A bilateral working group is being set up.
China has a year before the truce is reassessed.
How it chooses to use that time will affect the stability of the relationship between the world's two most powerful countries.