Did breakthrough in US fentanyl crisis start in China?

‘There was a supply shock: the purity of fentanyl fell,’ Keith Humphreys, a professor at Stanford University, says. Photograph: Angela Weiss/AFP/Getty Images

As Donald Trump travels to Beijing this week, fentanyl – and China’s role in its supply chain – remains an enduring point of acrimony in bilateral relations.

At a UN meeting in March, the US again accused China of failing to stop its chemical industry selling the precursors required to make the potent synthetic opioid, while China suggested the US was shifting the blame for its domestic drug problem.