The government has rejected advice from its own experts and moved to upgrade cannabis from Class C to Class B to avoid "risking the future health of young people".
However, Home Secretary Jacqui Smith did agree with the Advisory Council on the Misuse of Drugs (ACMD) in calling for health professionals to be encouraged to identify and offer help to people dependent on cannabis.
The ACMD report, written by doctors, police, judges and drug counsellors, said health departments should also look at combining cannabis treatment programmes with those aimed at tackling dependency on tobacco, alcohol and other substances.
The report said scientific evidence pointed to a "probable, but weak, causal link between psychotic illness, including schizophrenia, and cannabis use".
Despite this they felt cannabis played only a "modest role" in the development of these conditions.
Research from 23 police forces in England and Wales indicates that four-fifths of cannabis seized on the streets is now the extremely potent "skunk" variety, which has been blamed for causing mental health problems, especially in young users.
Rejecting the advice not to reclassify cannabis, Ms Smith said: "Where there is a clear and serious problem, but doubt about the harm that will be caused, we must err on the side of caution and protect the public."