The "legal high" drug mephedrone should be immediately "quarantined" before a decision is made about its legality, according to a drugs counsellor.
Sarah Graham, who is also a recovering addict, told Today presenter John Humphrys that the drug, which is said to have caused a number of deaths, is being marketed directly at young people.
But Jeremy Sare, a former head of drug legislation at the Home Office, said that an immediate ban would be "a simplistic response to a scientific problem".
The Home Secretary is planning to announce this morning that the drug will no longer be legal. But one of the members of the Advisory Council on the Misuse of Drugs has resigned, which could prevent the drug from being banned immediately.