and Harvard Public Health does too;
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Psychosis. Marijuana exacerbates psychotic symptoms and worsens outcomes in patients already diagnosed with schizophrenia or other psychotic disorders. Several large observational studies also strongly suggest that using marijuana — particularly in the early teenage years — can increase risk of developing psychosis.
An often-cited study of more than 50,000 young Swedish soldiers, for example, found that those who had smoked marijuana at least once were more than twice as likely to develop schizophrenia as those who had not smoked marijuana. The heaviest users (who said they had used the drug more than 50 times) were six times as likely to develop schizophrenia as the nonsmokers.
Until recently, the consensus view was that this reflected selection bias: Individuals who were already vulnerable to developing psychosis or in the early stages (the prodrome) might be more likely to smoke marijuana to quell voices and disturbing thoughts. But further analyses of the Swedish study, and other observational studies, have found that
marijuana use increases the risk of psychosis, even after adjusting for possible confounding factors.
Although cause and effect are hard to prove, evidence is accumulating that early or heavy marijuana use might not only trigger psychosis in people who are already vulnerable, but might also cause psychosis in some people who might not otherwise have developed it.
Certainly genetic profile mediates the effect of marijuana. People born with a variation of the gene COMT are more vulnerable to developing psychosis, for example. Because there is as yet no reliable way for clinicians to identify vulnerable young people in advance, however, it is safest to restrict use of medical marijuana to adults.
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http://www.health.harvard.edu/newsletters/Harvard_Mental_Health_Letter/2010/April/medical-marijuana-and-the-mindand this:
How cannabis can trigger schizophrenia
Smoking cannabis affects brain chemistry so seriously it can trigger schizophrenia, scientists warn today.
Researchers have found the first evidence that marijuana can cause genetic abnormalities associated with the mental illness, which affects about one in every 100 people.
Many scientists have been warning for years that cannabis can trigger hallucinations and delusions similar to symptoms found in schizophrenia.
Previous studies have suggested that using the drug before the age of 18 raises the risk of the condition in later life by six-fold.
Its ability to cause psychotic conditions is probably related to long-term changes in the brain caused by a substance found in marijuana called tetrahydrocannabinol (THC).
THC affects chemicals in the brain that transmit information from one nerve cell to another.
Disrupting the delicate chemical balance can result in memory loss, anxiety and other conditions.
The new Japanese research was led by clinical psychiatrist Dr Hiroshi Ujike of Okayama University and reported in the journal Molecular Psychiatry.
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Read more:
http://www.dailymail.co.uk/health/article-126056/How-cannabis-trigger-schizophrenia.html#ixzz2rtozzfjb
and this too:
Legalize Pot? The “Harmless” Drug and Schizophrenia
By Cassie Rodenberg | July 11, 2011
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The frightening part lies not in the drug’s immediate addictive effects but in what marijuana can trigger. Studies show that marijuana increases the risk of psychosis, a loss of contact with reality, in children and adolescents predisposed to mental illness by 40% in their lifetime,1 meaning marijuana can cause predisposed mental illnesses like schizophrenia to blossom. Though this is a relatively rare occurrence, it’s especially important to note for families with young adolescent children and a history of mental illness in the family. In more frequent pot users, this already staggering percentage can escalate to a 50-100% lifetime risk of psychosis for those genetically predisposed. Some mental illnesses may never begin without marijuana’s influence.
Studies have even gone so far to say that marijuana causes psychosis, saying that if the drug was never used, the population would have about 8% less schizophrenia incidence rates.2 To top it off, marijuana can shake and derail the brain’s neural pathways among cannabinoid and dopamine receptors, what’s in charge of our emotional and motivation processing, which may be the root of emotional processing problems seen in addiction and schizophrenia disorders.3
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http://blogs.scientificamerican.com/white-noise/2011/07/11/legalize-pot-the-harmless-drug-and-schizophrenia/
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