Prof Iversen believes cannabis has been "incorrectly" classified
A retired professor who said cannabis was one of the "safer" recreational drugs has taken over as chairman of the government's drugs advisory panel.
Pharmacology specialist Les Iversen replaced David Nutt, who was sacked by the home secretary last October for "lobbying" against government policy.
Prof Iversen said: "I think cannabis for the time being is past history."
He said much more active attention was currently being paid to so-called legal highs such as mephedrone.
Last year, Home Secretary Alan Johnson accused Prof Nutt of "crossing a line" into politics.
Prof Nutt is setting up an independent drugs panel to rival the Advisory Council on the Misuse of Drugs (ACMD).
Since that sacking, Prof Iversen, formerly of Oxford, has chaired the council's meetings.
Following his interim appointment, Prof Iversen told the BBC: "I'm not the drug adviser to the government, I'm a spokesman for a large group of people on the advisory council, only a few of whom are scientists."
In an article in 2003, he wrote that cannabis had been "incorrectly" classified as a dangerous drug for nearly 50 years and said it was one of the "safer" recreational drugs.
During his career, the professor's research has focused on the effects of drugs on the brain.
BBC home affairs correspondent Danny Shaw said the appointment of Prof Iversen appeared to be an attempt by the Home Office to restore calm to the advisory council after a turbulent few months.
Home Secretary Alan Johnson said: "The ACMD makes a valued and important contribution to our understanding of drugs and their harms. I'm pleased Prof Iversen will be bringing his experience to the role of interim chair.
"The council's work continues, including a forthcoming assessment on the harms of the so-called 'legal high' mephedrone, following on from our control of GBL, BZP and others late last year."
Prof Nutt was sacked for calling cannabis less harmful than alcohol and nicotine, and saying it had been upgraded to Class B for political reasons.
Five other members on the panel subsequently resigned.
In the weeks that followed, the home secretary tried to smooth over the row by making a number of concessions to his drugs advisers.
Prof Nutt was sacked after criticising the reclassification of cannabis
Mr Johnson agreed to write to panel members to explain any decisions that went against their advice.
He also said he would not pre-judge decisions on drug classification ahead of the committee issuing advice.
However, work on the advisory council is understood to have "slowed down" and a number of meetings were postponed in the wake of the row.
The Home Office has since said it could take two to three months to fill the vacancies left by the other resignations.
Prof Nutt will hold the first meeting of his new Independent Council on Drug Harms on Thursday.
He said five current members of the government's panel have agreed to attend.