Since it was downgraded in 2004, the number of people using cannabis has fallen, but the strength of what is on sale in the UK has shot up.
It is because of concerns over a link between stronger "skunk" and mental health problems like schizophrenia that persuaded Gordon Brown to check if it should be switched to class B again.
His advisors are going to hear from people like the Association of Chief Police Officers, who want it upgraded to help target crime gangs who grow the drug.
Have your say: Should cannabis be reclassified?
Assistant Chief Constable Simon Byrne said: "In one force alone we saw a 63% rise in cannabis farms last year.
"It is not just an urban phenomenon. It takes place in cities, in towns, in villages."
Longer sentences
If cannabis was made Class B, alongside amphetamines like speed, the maximum jail term for possession would go up from two to five years.
Paul Corry from charity Rethink says there could be better ways to put people off, like getting tobacco companies involved.
He said: "To put mental health warnings on cigarette rolling papers, we think that would be one very practical step that would lead to a long term reduction in the use of cannabis."
The Advisory Council on the Misuse of Drugs will make its recommendation in a few months but politicians will have the final say on whether to change the law again.
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