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Marijuana and Mental Illness: What's the Relationship?

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As mentioned previously, there's intense interest among mental health researches about the relationship between marijuana use and mental illness.  Several past studies have suggested a link between marijuana use and risk of psychosis, but untangling the relationship has been tricky.  On the one hand, lots of people use marijuana and don't develop major mental illnesses like schizophrenia.  So, perhaps the relationship is just happenstance.  Yet other research suggests that for some, marijuana really can worsen existing mental illness and perhaps trigger episodes of psychosis for those with family histories of schizophrenia and psychotic illnesses.  After all, marijuana is a powerful psychoactive drug. 

Maia Szalavitz has a well-balanced article in July 21st issue of Time magazine which includes this assessment:

That marijuana can have such incompatible effects in schizophrenia patients -- enhancing mood while exacerbating hallucinations and delusions -- is not surprising, when its chemical makeup is considered. One chemical called delta-9 tetrahydocannabinol (THC) is known to cause hallucinations and in high doses can even make healthy people feel paranoid or suffer brief attacks of psychosis. But another component of marijuana called cannabidiol (CBD) has anti-psychotic effects.

Indeed, there's much we don't know about marijuana and the various chemicals it contains likely have a variety of effects depending on dose and the individual user.  That the human body contains its own endocannabinoid system suggests that legitimate medicinal purposes are likely, but that in no way means that it's harmless. 


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Indeed, as with all drugs that affect the brain, there is harm in abuse. Cannabis is no different in that respect when it comes to people with conditions such as schizophrenia.

However, there is a degree of risk that is never discussed when this issue surfaces. That is, there is a link between a defective COMT gene pair and the way cannabis affects these genes. At present it is based on theory. A study conducted in New Zealand revealed the following.

There is a gene pair in the human brain that controls dopamine flow, COMT. It is thought that we can cope fine if both genes are OK, and even if one is defective. However, in an estimated 2% of the population, both of the gene pair *may* be defective. This is where the problem starts. Scientists think that when the defective gene's cannabinoid receptor receives THC, it cannot control the dopamine flow and allows an uncontrolled flood, resulting in a possible psychotic episode.

Now, schizophrenia affects 1% of the Australian population. I believe that the latest research suggests about 8% of the Australian population smokes cannabis at least once a year (we're not talking just chronic useage here). Therefore, it is logical to assume that of the 8% of the population that smokes pot, at worst, maybe 2% of them might have schizophrenia, or be at risk of developing it. You should also note that the defective gene is not present in all those who are at risk of schizophrenia. So, the figures below are a 'worst case' scenario.

This gives us an at risk number of people in the whole spectrum of cannabis users (occasional to daily), at the very outside, 32700 people out of 22 million may be at risk of having a psychotic episode and/or developing schizophrenia. For more information, see here:
ABC Catalyst Australia

The risk factor of someone becoming suicidal after taking a common anti-depression drug is about 33%. In Australia, it is conservatively estimated that some 200 thousand people are on anti-depressants, meaning roughly 66 thousand of them are at risk of becoming suicidal whilst taking a prescribed drug.

More information about some misconceptions about cannabis and cannabinoids can be found here:
How Much Can A Koala Bear?


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