The British government said today it would review its 2004 decision to reduce the penalties for possessing and selling cannabis.
Prime Minister Gordon Brown said Home Secretary Jacqui Smith would consult "on whether it is now right that cannabis should be moved from Class C to Class B".
Under its current classification, introduced by former Home Secretary David Blunkett, possessing small amounts of cannabis generally no longer leads to arrest.
But concern that stronger strains can cause mental illness has prompted calls for tougher penalties for its sale and use.
Last year Blunkett's successor Charles Clarke conceded that the 2004 downgrade had confused the public about the legal and medical consequences of using the drug.
A Home Office spokesman said the classification would be reviewed "given the increase in strength of some cannabis strains and their potential harms."
Moving cannabis to Class B would put it on a level with barbiturates and amphetamines, with possession leading to up to five years in jail.
It is currently classified at the same level as tranquilisers and anabolic steroids. Mr Brown said Ms Smith would publish a drugs consultation document next week.
"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," Mr Brown said in parliament.