At the request of my right. hon. Friend the Home Secretary, the Government’s advisory committee on drugs, the Advisory Council on the Misuse of Drugs (ACMD), carried out a substantial review last year of the harms associated with cannabis use, including the physical and psychological effects of cannabis. The report, ‘Cannabis: Classification and Public Health (2008)’, was published in May 2008 and copies have already been placed in the Library.
Additionally, the Department commissioned a systematic review of studies relating to cannabis and mental health. The peer-reviewed results of this review were published in the Lancet in July 2007 and confirmed the evidence of an association, possibly causal, between prior cannabis use and later development of psychosis and schizophrenia with a 40 per cent., increase in risk reported, up to a 200 per cent. increase for at-risk heavy users.