Mephedrone is likely to be made a Class B drug, the Government's chief drugs advisor indicated today.
Professor Les Iversen, the chairman of the Advisory Council on the Misuse of Drugs (ACMD), said his personal view was mephedrone was "amphetamines by another name".
In evidence to the Home Affairs Committee, he said any deaths linked to the drug were a "tragedy".
But he defended the need to conduct research into the effects of mephedrone - known as M-Cat or Miaow Miaow - before it was banned.
Addressing the MPs he said: "I am not here to give my personal views...but as a pharmacologist these drugs are amphetamines by another name and I know that amphetamines are harmful.
"I think you can deduce my conclusions from that."
Amphetamines are currently a Class B drug along with cannabis.
Putting mephedrone in Class B would mean carrying the drug would be punishable with a jail term of up to five years and dealing it with up to to 14 years in prison.
The Committee's chairman Keith Vaz said he would be writing to Home Secretary Alan Johnson to complain about the delay in banning mephedrone.
He said: "We will be writing following this session to the Home Secretary about these matters.
"We just think the delay is most unsatisfactory given the dangers that are inherent (in taking mephedrone)."
The ACMD is due to present its report on mephedrone to ministers on Monday afternoon.
At that stage ministers are likely to indicate that they are in favour of a ban, but it could be many months before a ban comes into force.
Prof Iversen said it was "remarkable" how quickly the fashion for taking mephedrone had grown.
And he said a temporary ban while the evidence was being considered would not be effective.
In order for a ban to work, it would need to include the entire category of drug and not just individual substances, he said.
Ministers faced criticism for not having banned mephedrone following the deaths of two teenage boys in Scunthorpe last week.
The families of Louis Wainwright, 18, and Nicholas Smith, 19, joined calls from teachers' leaders for an immediate ban.
Police are today investigating the death of a 24-year-old woman thought to have taken the drug in Norton, North Yorkshire.
Mephedrone was virtually unknown until early last year but it is now one of the most popular drugs in nightclubs and is widely available online.
It is usually a white or yellowish powder, which is snorted, but can also be obtained in pills and capsules.
Users report effects similar to cocaine and ecstasy but also suffer side-effects such as heart palpitations, high blood pressure and nose bleeds.
Other side-effects are said to include weight loss, insomnia and psychosis.
Liberal Democrat home affairs spokesman Chris Huhne said: "Professor Iversen is completely right to say the Advisory Council on the Misuse of Drugs must be allowed to conduct proper research before mephedrone can be made illegal.
"It is a travesty that the Government's interference with the advice of its independent scientific advisers has delayed this drug from being banned."
Shadow home secretary Chris Grayling said: "This is a welcome development. But the Government was warned years ago about the risks posed by legal highs and these steps should have been taken long ago."