But there is a warning from Katri Abel-Ollo, who has closely observed fentanyl's rise.

BBC: Synthetic drug fentanyl causes overdose boom in Estonia

Only four days later did the health minister, Yuri Shevchenko, say that the gas was an unspecified derivative of fentanyl.

ECONOMIST: Vladimir Putin's government pushes the questions away

The big question - that none of the experts in Tallinn can really answer - is why fentanyl has taken such a hold in Estonia, but not elsewhere.

BBC: Synthetic drug fentanyl causes overdose boom in Estonia