The Government's former top drugs adviser has warned banning the dance drug mephedrone could do more harm than good.
Professor David Nutt said a "new approach" to dealing with synthetic drugs was needed.
He also suggested the regulated use of drugs like mephedrone and ecstasy in controlled environments, such as clubs, may be the way forward.
Home office minister David Hanson earlier announced mephedrone could be made a class B drug by April 16.
Home Secretary Alan Johnson has laid a draft order before Parliament to approve a ban on the substance, which is also known as M-Cat or miaow miaow, and similar cathinone derivatives.
The drug has been linked to up to 25 deaths in England and Scotland.
Mr Hanson said chairman of the Advisory Council on the Misuse of Drugs (ACMD) Les Iversen, had made clear "the harms that these drugs undertake justify control" under the Misuse of Drugs Act.
But Prof Nutt, who was sacked as ACMD chairman after saying ecstasy was less harmful than alcohol, criticised the Government's "knee-jerk" approach to mephedrone.
He said the Government should have waited for the results of a study from The European Monitoring Centre on Drugs and Drug Addiction, which is due to report in July.
He also criticised the Government's "knee-jerk" reaction over the "supposed problem" which has been "whipped up" into a hysteria.