I think the people who staff Psych Wards know this correlation and possible causation, already. They've suspected it for years. How many times can you see a young person, (a) almost always male, (b) who is a known pot user, come in with (c) a psychosis (schiz; bipolar) and not make the 'connection'?

Looking back, I recall several of these schoolmates, with their strange ideas and behaviour, where it escalated into delusions, magical thinking, paranoia, and hallucinations, also.

e chase, toronto, canada

The whole thing hinges on "if we assume a causal relationship".

If one of my 7th grade science students used that line in a presentation, he'd get a failing grade.

Peter, New York, NY

is this a causal or correlational study? Going from a class C to class D drug, just under tobacco and alcohol, is an indication of the parameters used by the FDA. The effects of the chemical in the brain are different and occur under different general bodily conditions. Alcohol causes terrible hallucinations -- said to be of insects and/or spiders -- permanent damage to the brain, and irreversible damage to the liver. The hallicinations caused by cannabis are related to relaxed and low muscle tone to the lens of the eyes and the frontal cortex or even semiotic association happens by gestalt. A personal interpretation of something out of focus could yield the same "hallucination." In other words, there is so much that is lacking in the study of the effects of marijuana. It's a pity, because I would really like to know.

Luke, Garden City, USA/NY

I firmly believe that people who smoke cannabis regularly will develop schizophrenic symptoms. I have observed a family member who had smoked with a combination of alcohol and the personality change is horrific! When (this) family member ceased smoking the symptoms took a while to subside. It is so difficult to prove that it is the cannabis because psychiatrist will immediately medicate for schizophrenia/bipolar... This family member is now afraid to not take schizophrenic medication because they believe it is the cure and not the fact that they stopped smoking and drinking....

A study needs to be done, tracking someone who has been diagnosed with schizophrenia, long term smoker, but has quit with no psychotrophic meds.... I bet you'll find that the smoking was the cause.... My heart goes out to people who have gotten caught up in trading one medication for another , when all they had to do was change their lifestyle!!!

Gwen Martin , Oakland, Oakland, Ca

I completely disagree with this article. Presently I know two people with schizophrenia who never ever smoked pot and two people who have and continue to smoke pot for over 20 years and guess which two people have schizophrenia.

The non-pot smokers of course! As far as I am concerned, this is just another falses excuse to keep a ban on pot.

By the way, I have never ever smoked pot. Does that mean I am at an increased risk for schizophrenia?

Gloria Lynn, California, USA

I have first hand experience of this. I have never been a smoker of any kind let alone pot. I presently have a girlfriend who has smoked cannabis regilarly for the last 20 years and it is my belief that is responsible for her sate of mental health. She suffers tremendous anxiety attacks, palpatations ans great insecurity problems. Because of these feelings she finishes our relationship very frequently and indeed regularly. I love her very much but her jealous tendancies (which I believe result from what I have said previously) are making my life nearly impossible to live.
I say ban Cannabis totally because mankind doesn't know what to expect from the abuse of this drug and I believe that future mental health figures will rocket!!

stephen hall, manchester, UK

Yeah man - like we totally know that smoking weed doesn't cause mental problems... totally.... ummm.... what was I talking about?

grogbutt, Vancouver, WA

Hello Everyone, I used to be a pot smoker! Why, I do not know...Addicted-habit, whatever you want to call it. Never thought it was that bad...The saying was I'd rather smoke than have a drink. Everyone I talked to about it would say smoking did not effect you as much as drinking. Well I guess I was DEAD wrong...! We all need to inspire our children somehow to be sober...Drug free... Is it possible to have fun without the buzz? Let's all get real. These children are our future...We the people need to be there. Be an example. I know we have to be realistic and there will always be drunks and addicts, but possibly we could be honest with ourselves today not tomorrow... I hear there is alot of fun out there without the BUZZ ON...Let's show the kids that this is TRUE!

Noreen Adams, Cohasset, America/MA

Cannabis has never in any form been proved to have any link to ANY detrimental side effects. The Reefer madness experiments were little more than experiements paid for by pharmaceutical companies and corrupt government officials with agendas to push through that which they wish. Would they like to study true drugs effects on the pysche like Geodon? Or leave those alone because 'scientists' and pharmaceutical companies certified these 'death cocktail' drugs. That's right america spend lots of money and go after cannabis smokers of whom there are millions..which obviously the schizophrenia take does not hold at all due to the sheer number of smokers, Of course when you look at true case studies and the diagnosis of schizophrenia you see these things are easy to manipulate as well. An herb..an HERB with no physically addictive qualities, in fact it is no more addictive than McDonalds food, and everyone is having a cow. Grow up, start thinking for yourself, instead of letting others

Daniel, Jamestown, Tennessee

So then are we to assume that in areas of the world where the most potent marijuana has been grown and widely used for centuries, that there is widespread schizophrenia on a scale beyond comprehension in the western world?
This story just sounds to me like a re-hash (pardon the pun) of the same old scare stories.

Also, being 51 years old, I remember the potency of marijuana 30 years ago compared to today.
I've not seen any marijuana today, that is more potent than the most potent in the mid 1970's.
MAYBE the potent grades are more easily available today on average, but they aren't any more potent than 30 years ago.

Ed, Indianapolis, Indiana, USA

They made it up. There's a profit for someone behind the scenes.

dj, seattle, wa

What was the population growth %'s for the same time period ?

S_a_H, Lubbick, tx

The above is such nonsense it smacks of the reefer madness stories of the 20's.

Why has the article missed 2 recent important studies on drugs.THe RSA report of 8th March and the one reported on Friday in the Guardian re Alcohol worse than ecstasy on shock new drug list by James Randerson Both of these reports by high ranking Goverment advisors show that present day illegal drugs such as Ecstasy and LSD along with Cannabis are less harmful than the current legal drugs alcohol and Tobacco.

All this nonsense about cannabis being 20 times stronger than it was 20 years ago is just that nonsense.The goverment sponsered report of 24th March categorically refutes this claim saying the true figure is around 2 to 3 times stronger.

My reading of the situation is the Goverment is runing scared of the scientific evidence of the relative safety of these drugs in comparison to the legal drugs. Million of people use cannabis in total safety.It is time we ended this Prohibition its stupid.

J Leeson, Sheffield, S Yorkshire

Can we assume that this study controlled for the presence of other drugs? After all, pot smokers are very often consumers of other drugs, including hallicnogens, use of which can certainly lead to mental health issues.

ent, Illinois, USA

Cannabis must be treated with increased suspicion in the face of ongoing research that suggests it is far from benign. It is an extremely complex and varying collection of powerful chemicals. That alone indicates the need for careful consideration and much more investigation. Unfortunately, the government's ham-fisted law enforcement approach has convinced generations of people that the government cannot be trusted to tell the truth about cannabis or other drugs. The solution is to have independent research from respected non-government sources with results communicxated directly to the public, not through government or mainstream media middlemen, to preclude the results bering spun to fit their political agenda.

R LaBonte, Sacramento, California

I think all medical studies that try to accurately identify a specific consumable and its cause and effect on health needs to be viewed as a whole with other consumables. To say any one thing causes ill effect simply because it is consumed is ignoring all other things one has ingested at the same time, purposely and not. I think it is much more accurate to say marijuana, because of its in herent effect in brain chemistry, is more like a risk factor that when combined with several other risk factors, can have adverse effects.

Eric, Tucson, az

I wouldn't say that it (getting high) causes anything, but it definitely unlocks a door in the mind that for some people should remain permanently closed.

Mr. Reefer: How many people are on heroin compared to those who smoke weed? Which is the bigger problem? I guess that's subjective. Most people know that heroin is bad, really bad. A lot of people (and you prove this with your comment) still see weed as "no big deal".

L., Dublin, CA

I don't see anything wrong with casual use. It's the heavy use that need to be addressed. It can lead to serious apathy... There are far more problems stemming from Heroin use. I've never tried, nor had the desire, to try any "Designer Drugs" such as Cocain or Heroin, so does Cannabis use really lead to more serious substance use??? I think alcohol destroys more lives than any "drug".

Mr R eefer, Kingston, Jamaica

I believe this as our son was a heavy mj user in highschool and college he was diagnosed with schizophrenia in college. We wondered at the time which came first and if the mj triggered a latent predisposition or if he was self medicating.

I studied schizophrenia and joined peer parent groups and the correlation was too prevalent to be ignored.

Mary, Norman OK,

This explains the American Democratic Party leadership.

Diogenes, New orleans, Louisiana

but the voices are telling me to smoke Cannabis

mark, atlanta, USA_GA

Now, thanks to the stupidity of such as Rosie Boycott who spent so much effort trying to persuade people to decriminalise cannabis, it will be a case of "for whatsoever a man soweth, that shall he also reap.": In this case quite literally so.

The risk of serious psychological harm that can be caused by use of cannabis is on a par with some Class 'A' drugs. Accordingly it should be so reclassified and possession or dealing met with suitably condign sentences.

M Cazador, The Hague, NL

Recall reports from the Middle East of societies of great lassitude where drug use was high.

Richard, Dubuque, USA/Iowa

Reasonable men avoid risks even if the precise mechanisms and details of those risks are uncertain. Those posters and readers who reject the article ought to take a closer look at the abundant medical evidence that cannabis use increases the risk of schizophrenia and has numerous other harmful effects. I doubt that many schizophrenics who used cannabis reckon, in their lucid moments, that even if the ganja caused (or prompted) their mental illness, it sure was worth it, or that they were fully justified in waiting for conclusive proof of causation.

Ken Muszynski, Tallahassee, Florida, USA

I worked in mental health and many people with mental illnesses used all kinds of drugs before they were officially diagnosed. We used to call them "self medicators". Alcohol was the main one, I wonder what kind of correlation they could find between use of alcohol and schizophrenia, I bet it would be even stronger than marijuana. I think this research is politically motivated to find something wrong with marijuana.

Michael , Napa, CA, USA

i beleve cannabis is couse schizopherenia, i'm a nurse and research to people who had a schizopherenia most of them used cannabis when they were between age15-24 the young people deserve to know how cannabis dangours for them

azadeh, LONDON, UNITED KINGDOM

Causality can work in two directions. Who is to say that people in the early onset of mental illness are not more prone to taking cannabis? All you can say from such studies is that there is a correlation between mental illness and substance abuse - you cannot infer which direction the causality goes.

Stephen J. Brown, Cambridge, UK

The conclusions of this study are completely flawed by assuming the very question they are asking.

1) The study says IF the causal link is accepted between cannabis use and developing schizophrenia, but does not prove the causal link and just asks us, in John Macleod's own words, to "suppose" it is true.

2) It takes predicitons based upon heavy users and then extrpolates them to light users, akin to saying if a man might get liver disease drinking 10 pints of alcohol a day, then everyone who drinks 1 pint a say also will get liver disease.

I know many cannabis users including; doctors, professors, lecturers, lawyers, succesful business people, social workers and many more. None of these people have schizophrenia or are ever likely to have. They are all extremely stable people. It is more likely that a person's social background and circumstances and their psychological history are the important causal factors behind schizophrenia. This is not science, it is sensationalism.

Harry Sanders, London,