A new drug is reported in Europe at a rate of about one every week.
The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) said some 50 new substances have already been detected this year.
A total of 49 new "psychoactive" substances were officially notified for the first time in 2011, the EMCDDA said, up from 41 in 2010, and 24 in 2009.
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And preliminary data for 2012 showed no signs of a decline, with more than 50 already detected this year.
The agency said Europe faced an increasingly complex stimulant market.
Cecilia Malmstrom, European Commissioner with responsibility for the EMCDDA, said: "Stimulant and synthetic drugs play a central role in the European drug situation, creating a market which is fast-moving, volatile and difficult to control. Data from emergency rooms, toxicology reports and drug treatment centres indicate that the associated risks are not always well known by the users."