Cannabis laws have proved controversial
Laws making possession of cannabis a largely non-arrestable offence could be reversed, Gordon Brown has said.
The prime minister told MPs a consultation on reclassifying cannabis will be launched next week as part of a review of the entire UK drugs strategy.
The drug was downgraded to class C - which includes things such as anabolic steroids - from class B, which includes things like amphetamines, in 2004.
But there are fears more harmful forms of the drug have become available.
A Home Office spokesman said the Advisory Council on the Misuse of Drugs (ACMD) will be asked to review reports that danger from cannabis is increasing due to wider availability of more potent strains such as "skunk".
There is concern stronger varieties of the drug can cause mental health problems.
Mr Brown said the Cabinet had discussed the issue and Home Secretary Jacqui Smith would publish a consultation document next week about the UK drugs strategy.
Mr Brown told MPs at prime minister's questions: "She will be asking the public to comment on new ways in which we can improve drugs education in the country, give support to people undergoing treatment... and give support for communities who want to chase out drug dealers from their communities."
He was responding to a question from Labour MP Martin Salter who, referring to the medicinal use of cannabis, urged a drugs policy that did not "criminalise the sick but tackles the drugs that do the most harm".
Shadow Home Secretary, David Davis, commenting later for the Conservatives, said: "We would welcome the reclassification of cannabis. Drugs are a scourge on society and a major cause of crime which Labour has failed to tackle.
"We have long called for the reclassification of cannabis based on the science and evidence available which shows all too clearly the real damage this drug can do to people - especially young people.
"But it is not enough to simply consult on this - the government must also secure our porous borders to stop hard drugs flowing into the country and seriously strengthen drug rehab treatment for those already on drugs."
The issue of downgrading - or even decriminalising - cannabis has proved controversial and has already been reviewed once by the Home Office.
The original move from Class B to Class C was made when David Blunkett was home secretary.
His successor Charles Clarke asked for a review in 2005.
At that time the ACMD said that while cannabis was undoubtedly harmful it was still less harmful than other drugs like amphetamines which are in Class B. It recommended no change.
But it also called for urgent further research on the potency and pattern of cannabis use.
If the ACMD were to back a change in classification and the Home Office accepted its recommendation, it would require agreement of both houses of Parliament to become law.
A Home Office spokesman said: "We will be asking the ACMD to review the classification of cannabis, given the increase in strength of some cannabis strains and their potential harms.
"It would be wrong to prejudge that review which shows how seriously we take our priority of reducing drug-related harm."
The Home Office's drugs information website, Frank, includes details of new more potent varieties of cannabis.
It says: "Recently, there have been various forms of herbal or grass-type cannabis that are generally found to be stronger than ordinary 'weed', containing on average two to three times the amount of the active compound, THC.
"These include sinsemilla (a bud grown in the absence of male plants and which has no seeds), homegrown, skunk (which has a particular strong smell) and netherweed."