A ban on synthetic stimulant mephedrone has come into force across the UK.
The drug and its related compounds are now Class B substances after measures were rushed through Parliament.
The Advisory Council for the Misuse of Drugs (ACMD) had recommended a ban, saying the substance was "likely to be harmful" despite incomplete research.
But the leading medical journal The Lancet has questioned the ban, saying it had been rushed and politics had been allowed to "contaminate" science.
Mephedrone, also known as Meow, Bubbles and MCAT, is derived from cathinone, a compound found in a plant called Khat.
The laboratory-produced drug has a similar effect to amphetamines, ecstasy or cocaine. But it also causes nausea, palpitations and vomiting.
The drug has been linked to a number of deaths but there has been no conclusive scientific proof yet that it has been responsible for any of them on its own.
Under the drug classification rules, anyone found carrying Mephedrone could face up to five years imprisonment - while dealers could receive up to 14 years.
The Association of Chief Police Officers urged forces to target dealers, saying that it had no intention of criminalising young people who had been using it.
In the days running up to the ban, police officers and local councils approached retailers who were selling the drug asking them to voluntarily surrender supplies.
A number of websites that were selling the drug have also closed down.
But in an editorial timed to coincide with the ban, The Lancet medical journal said the manner in which Mephedrone had been dealt with signalled a "collapse in integrity of scientific advice in the UK".
It said the advisory council had been still discussing its own draft report into Mephedrone-like substances when its chairman briefed the home secretary on a recommendation to ban them.
"Equally notable was the very quiet release on the same day of the ACMD's other report a detailed progress report on recommendations made in 2006 on hazardous drug use," said the journal.
"The report contains some potentially unpalatable conclusions on tackling young people's problems, including not enough being done on alcohol and tobacco, as well as calling for a review of the Misuse of Drugs Act 1971.
"Yet this report received no media attention or a response from the Home Office. Instead, it conveniently got buried under discussions on the legal status of mephedrone."
The Lancet said: "It is too easy and potentially counterproductive to ban each new substance that comes along rather than seek to understand more about young people's motivations and how we can influence them."
Two members of the committee quit in quick succession during the row over the Mephedrone.
One, Dr Polly Taylor, said she feared the government would interfere with the council's scientific advice. The second, Eric Carlin, said there had been no proper discussion of the effect a ban would have on the behaviour of young people.