Sorry folks, you are missing the joke I was trying and obviously failing to make with my comment.

I am very well aware of the synthetic nature of fentanyl and most of the other opioids we use, the point i was making was that one of the slang or street names for fentanyl amongst drug abusers is 'synthetic heroin' because they regard it as a 'fake' heroin substitute. Its also known as china white. Apparently it is quite popular because it provides a rather more mellow, pleasant high than heroin.