Doctors say it's 50 times more potent than heroin, and just a tiny amount can kill you.
Police fear the medicinal drug Fentanyl is taking hold in this country after claiming thousands of lives in America.
The mother of a teenager from Deal in Kent, who died from an overdose, has now spoken about the dangers.
Robert Fraser, who was 18, was found dead in his bedroom.
Tom Savvides talks to Michelle Fraser and Ian Cruxton from the National Crime Agency.