designer drug 
noun
A synthetic analogue of a legally restricted or prohibited drug, devised to circumvent drug laws.MDMA, or Ecstasy as it is more commonly known, is an amphetamine-like designer drug from the late 1970s....
- It's the story of a streetwise American master chemist who heads to England to set up the deal of his lifetime - introducing a new designer drug, POS51, to the European market.
- Quickly thereafter the drug made its way over to Europe and in the early 80s in Britain it was a designer drug only used by wealthy clubbers and pop stars.