A STUDY by North Staffordshire academics has rejected a link between smoking cannabis and an increase in mental illness.
The research found there were no rises in cases of schizophrenia or psychoses diagnosed in the UK over nine years, during which the use of the drug had grown substantially.
Pro-cannabis campaigners seized on the results as supporting the legalising of cannabis, and claimed the report had been suppressed.
But the leading expert behind the study said it could be too low-key to re-ignite the debate on whether restrictions should be removed from soft drugs.
From their base at the Harplands Psychiatric Hospital in Hartshill, the four experts reviewed the notes of hundreds of thousands of patients at 183 GP practices throughout the country to look for any changing rate in cases of schizophrenia.
The work had been set up to see if earlier forecasts from other experts had been borne out, that the mental disorder would soar through the growing popularity of cannabis.
Published in the Schizophrenia Research journal, a paper on the study said: “A recent review concluded that cannabis use increases the risk of psychotic outcomes.
“Furthermore an accepted model of the association between cannabis and schizophrenia indicated its incidence would increase from 1990 onwards.
“We examined trends in the annual psychosis incidence and prevalence as measured by diagnosed cases from 1996 to 2005 and found it to be either stable or declining.
“The casual models linking cannabis with schizophrenia and other psychoses are therefore not supported by our study.”
The research was conducted by Drs Martin Frisher and Orsolina Martino, from the department of medicines management at Keele University; psychiatrist Professor Ilana Crome, from the Harplands academic unit, who specialises in addiction; and diseases expert Professor Peter Croft, pictured below, from the university’s primary care research centre.
Its findings come shortly after the Government reclassified cannabis from Class C to Class B, which invokes heavier penalties.
Yet Dr Frisher revealed last night that the study had been partly commissioned by the Government’s advisory committee on the misuse of drugs.
He said: “We concentrated on looking into the incidence of schizophrenia during those years and not specifically at cannabis use.
“It was relatively low-key research so I don’t believe it will re-ignite the debate on whether the drug should be legalised.”
Hartshill-based Dilys Wood, national co-ordinator of the Legalise Cannabis Alliance, said that so far the report had been published in medical journals and would have a far-reaching reaction if it surfaced more widely.
She added: “I believe that if it had found a causal link between cannabis and schizophrenia it would have been all over the press.
“The public needs to know the truth about drugs; not more Government-led propaganda.”
And Alliance press officer Don Barnard said: “It is hard to believe the then Home Secretary Jacqui Smith did not know of this very important research when deciding to upgrade cannabis to Class B.”
The team said a number of alternative explanations for the stabilising of schizophrenia had been considered and while they could not be wholly discounted, they did not appear to be plausible.