sentences:  Fentanyl analogs have killed hundreds of people throughout Europe and the former Soviet republics since the most recent resurgence in use began in Estonia in the early 2000s, and novel derivatives continue to appear.As of October 2015, betahydroxythiofentanyl is a controlled substance in China.As of May 2016, betahydroxythiofentanyl is a Schedule I controlled substance in the United States.