Britain is being swamped by a "potentially dangerous" influx of so-called legal highs, the Government's drugs tsar has warned.
Professor Les Iversen, chairman of the Advisory Council on the Misuse of Drugs (ACMD), said he and his colleagues can not keep tabs on all the substances available as there are now around 200 such chemicals flooding the market.
Mr Iversen told a public hearing that dealers are dodging laws by dressing the drugs up as plant food and warned that overdose risks were "clearly immense".
And he said the ACMD, which reviews substances and advises whether measures should be taken for preventing misuse, would be focusing on a man-made amphetamine called Benzo Fury and new LSD-like chemicals.
Mr Iversen said: "This has become a high priority agenda item for the ACMD and will continue to be so for the foreseeable future as the new compounds continue to emerge.
"The European Monitoring Centre logged in 60 new compounds last year and there's been a similar rate this year. That's one a week.
"They list some 200 different psychoactive chemicals that lie outside the legal scope of our existing regulations.
"Our problem is to know how many of these are really being used in this country and how harmful are they and this is difficult because we can't possibly address all classes of compounds at once, unless we and the Government can think of cleverer ways of regulating."
Mr Iversen said the minute doses were hard to "comprehend" and were often supplied as a dilute solution dropped on a piece of blotting paper.
He went on: "However, we know it's also possible to buy powders of some of these new compounds, sprays, fluids and the dangers of overdose are clearly immense.
"So this is an area we're looking at with a great deal of caution and worry."
Mr Iversen said legal highs were a "world-wide phenomenon as dealers show "blatant misuses of the existing law" to sell the compounds legally.
He said: "Novel psychoactive chemicals are made in China one week and shipped here for human consumption next week without any safety data accompanying it. To me that's an appalling situation.
"Sooner or later we will get unexpected and serious harm emerging with one of these compounds and then we will blame ourselves for allowing them to be sold without the usual safety data.
"That's why I think this is a serious problem, it's not just a nice set of party drugs that we can let people get on with, it's a set of chemicals that are potentially very dangerous."
Last year, two legal highs - mexxy and black mamba - were made illegal class B drugs.