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Not To Worry, Potheads
About that study everybody in the media is screeching about regarding pot use causing schizophrenia...there was a terrific comment on The Wall Street Journal's Health Blog, that puts it in perspective:

Anti Drug Propaganda

Remember when the gov’t scare propaganda for drug use had to be realistic to have any effect? Me either. At one point there were racist suggestions that associated marijuana with rape and now, in the more PC age, we are being warned that it may contribute to mental illness.

Conclusion: The States guns should have greater control over our body, for our own good.

The MSM articles on the study (gated version at Lancet**1) have focused solely on the percentage increases in mental disorders without mentioning the rarity of psychotic disorders in the first place. One of the few articles that does mention the chances of developing such disorders puts the prevalence of schizophrenia in the US at 50 in 1000 or .005.**2

Using US Drug policy data we can estimate how much risk a 40% increase entails. Marijuana use is only listed by Last Month Used, but being the most popular illicit drug, so overall usage numbers are close enough. The NHS**3 survey on drugs puts the lifetime use for any illicit drug at an average of 36% from 1979 – 2001* which puts 36% of the population at a 40% higher risk for schizophrenia and the other 64% for normal risk. Using the general population schizophrenia rate of .005 as the risk factor gives marijuana users a .006118 chance of schizophrenia as opposed to the .00437 odds for someone with a lifetime of drug abstinence. There’s your 40% from about 4/1000 to 6/1000.

Buying two lottery tickets will double your odds of winning too. You can go from having the nearly same odds as being hit by lightening to…having nearly the same odds as being hit by lightning. And you’ll be down a buck.

Besides ignoring the unlikely event of mental disorder none of the articles have touched on any comparable risks. Anyone who suggests that this is a good reason to increase the penalty for marijuana use would surely be hypocritical if they didn’t suggest a total ban on alcohol. Its abuse, “is a stronger predictor of psychotic symptoms than regular cannabis use (by a factor of four).”*4




*The survey had gaps in some years but since the numbers were so consistent from year-to-year filling them in would not have a significant effect on the conclusions.

Comment by NBAT - July 27, 2007 at 12:34 pm

Posted by aalkon at July 27, 2007 6:48 AM


This line is telling about their methods:

Its abuse, “is a stronger predictor of psychotic symptoms than regular cannabis use (by a factor of four).

The word "predictor" is a dead giveaway to the fact that their research used regression analysis (not surprisingly - a true experiment here is unethical), which is a fancy form of correlation. From this we know there is a relationship between mental illness and drug use, but not the direction, or whether there are untested variables that influence both. Thus, it can be equally argued that those people predisposed to mental illness are more likely to use drugs as young people than those not predisposed to mental illness.

Considering also the base rate problem described above, this study seems to be much ado about nothing. But it sure makes for good propaganda!

Posted by: justin case at July 27, 2007 11:42 AM

I think that the biggest problem with this study is the there is a probable causation. It's just not what they were shooting for. Rather than smoking pot being a cause of psychosis, having a psychosis makes it more likely that one will smoke pot.

Hell, I use it to help manage my bipolar. Easier and cheaper to get that conventional meds, when you're one of the 45 million plus Americans without health insurance, like I am. I have been cutting back more and more, as my son gets older, relying instead on dimenhydramine (generic Dramamine), but the occasional toke is still exceedingly useful, when things get really bad.

I should add that several of my crazier friends, tend to be the most enthusiastic tokers. Oh, and I was bipolar before I ever smoked the pot

Posted by: DuWayne at July 28, 2007 12:57 AM

Drugs suck.

Posted by: Crid at July 28, 2007 1:27 AM

Drugs suck.

Does that include alcohol?

(Doctor and professor) Roy Walford told me he used to take coke when he wrote articles for journals. He wasn't a coke-head any more than I'm a Ritalin-head for using it as a tool to help my superball-brain stay focused when I'm writing. The difference: My Ritalin is legal and prescribed for me by a doctor.

I don't smoke pot because it makes me feel like somebody cold-cocked me with a frying pan, but I know people who do, and they haven't found it to be a "gateway drug"; ie, they're not in a gutter somewhere now shooting up. They continue to be occasional pot users.

Posted by: Amy Alkon at July 28, 2007 6:06 AM

> Does that include alcohol?

Yes. (hic)

Posted by: Crid at July 28, 2007 7:25 AM

Crid -

Drugs suck

So does not sleeping for days at a time and becoming increasingly incoherent. So does being unable to leave the apartment for days at a time. So does being unable to focus, due to superball brain (thanks Amy, I'll be using that one), altough in fairness, I should mention that I actually utilize superball brain in my professional life as a songwriter. I am always working on several songs at the same time - and bouncing about the blogosphere. But when I have to focus, caffeine is invaluable. Even better, would be if I could afford to fill the script I got for Aderall, but it will be a few more months before I can afford to get insurance, so caffeine suffices for now. Thankfully, my needs for much focus are rare and usually not extreme.

Posted by: DuWayne at July 28, 2007 12:01 PM

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