Cannabis use 'increases risk of schizophrenia'

[boulder]

Frequent cannabis use increases the risk of developing depression and schizophrenia in later life, according to three new studies published today.

 

Authors of the studies, from Australia, New Zealand and Sweden, all conclude that the authorities should introduce strategies to reduce cannabis use - particularly amongst minors.

 

In one study of 1,601 students from 44 secondary schools in Australia, frequent cannabis use appeared to result in a rise in later depression and anxiety in girls.

 

Daily use among the girls, who were studied from the ages of 14-15 for seven years, was associated with a more than fivefold increase in the odds of later depression and anxiety.

 

Weekly or more frequent use predicted a twofold increase in later risk. Another long-term study in New Zealand obtained information on psychotic symptoms of 1,037 children at age 11, assessed their drug use at ages 15 and 18, and then assessed psychiatric symptoms at the age of 26.

 

The study found that people who used cannabis by the age of 15 were four times as likely to show an increase in "schizophrenia symptoms" at the age of 26.

 

The last of the three studies, all of which are published in the British Medical Journal today, assessed results of an often- quoted 1969 study on the causes of schizophrenia.

 

The study, carried out on Swedish male conscripts aged 18-20 in 1969, concluded at the time that cannabis use did increase the incidence of schizophrenia. This conclusion was broadly supported by the third study published in the BMJ today.

 

Scientists from the universities of Bristol, Cardiff and Gothenburg discounted arguments that other drugs taken by the subjects invalidated the 1969 study.

 

Questions had also remained about whether the Swedish subjects took cannabis to relieve original symptoms of original mental disorders. Again, these were largely discounted by the new study through reassessment of study conditions and statistical analysis.

 

The link between cannabis and mental health disorders has long been well established and referred to by anti-drugs campaigners in Britain and abroad. But a low incidence of the disease and the fact that users often use other drugs as well as cannabis has created methodological problems.

 

Assessing the three latest studies, two Sydney university professors said in the BMJ that the pivotal question was: "Does cannabis cause these conditions, or do patients use cannabis to relieve their distress?"

 

Professor of child and adolescent psychiatry Joseph Rey and professor of psychiatry Chris Tennant argue that this question is still left "unresolved" by the three new studies.

 

However they conclude that the results "strengthen the argument that use of cannabis increases the risk of schizophrenia and depression". They add: "If true, the use of cannabis will contribute to more episodes or new cases of the illness. This should be food for thought for both clinicians and legislators."

 

Marjorie Wallace, chief executive of mental health charity Sane, said: "Recent research papers are increasingly confirming Sane's extreme concerns about the use of cannabis and its relation to mental illness.

 

"While cannabis may be harmless to many people, there is no way of telling who might be the vulnerable victim for whom its use can turn from a relaxing trip into a lifelong torment.

 

"The most worrying revelation of these studies is not just the immediate triggering of hallucinations but that cannabis can lead to psycho

 

The Guardian.