In August, I wrote about how Mexico's cartels are capitalizing on the fentanyl trade. Afterward, many people asked me how China fits into the equation. In tracking the flow and distribution of the synthetic opioid, The U.S. Drug Enforcement Administration's recently released 2017 National Drug Threat Assessment was ambiguous about the relationship between the Mexican cartels and China. Explaining China's role in its manufacture and its interactions with Mexican traffickers will require an examination of how two other cartel drugs — methamphetamine and heroin — intersect with fentanyl. The Rise of Illicit Fentanyl The danger posed by fentanyl first came to my attention many years ago when a friend who is an emergency room nurse told me about a man who overdosed on the potent opioid and died.