Users are dying of accidental respiratory arrest, and overdose rates have soared. China has not been blind to the key role its chemists play in the global opioid supply chain. Most synthetic drugs that end up in the United In States come from China, either directly or by way of Mexico, according to the DEA. China already has placed controls on 19 fentanyl-related compounds. Adding carfentanil to that list is likely to only diminish, not eliminate, global supply.