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, and the funeral is taking place today of a 19-year-old man who died after taking mephedrone on a night out.
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.
Speaking ahead of a lecture at Greenwich University, he said: "We need a new approach with dealing with these synthetic drugs.
"I wonder if there may be alternative approaches.
"I find it very difficult to support criminalisation of people who are using drugs which are less dangerous than alcohol."
He criticised the Government's "knee-jerk" reaction over the "supposed problem" which has been "whipped up" into a hysteria.
Prof Nutt said: "These knee-jerk reactions aren't dealing with the core of the problem.
"They need to have a proper, mature debate about how best to deal with drugs.
"Why don't we at least think about alternatives and allow people like me to mention them without being vilified.
"We regulate other drugs, alcohol and tobacco. Why are we so hostile to (regulating) new drugs?
"One way of reducing drug harm may be to regulate their use in controlled environments.
"Maybe we would allow clubs to sell small amounts of drugs, like mephedrone and ecstasy, in a safe environment, just like we sell alcohol.
"There is no scientific reason why mephedrone and alcohol should be seen as different."
The professor continued: "I hope that we start doing some very careful assessments of the consequences of making it illegal.
"We have to make sure there is not a rise in criminality, with gangs getting involved.
"We've heard already the Chinese are gearing up to make another drug.
"We will be in the same boat in a few more months, possibly with a more dangerous drug."
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