Study underlines cannabis link to psychosis

LONDON Tue Mar 1, 2011 7:56pm EST

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LONDON (Reuters) - People who use cannabis in their youth dramatically increase their risk of psychotic symptoms, and continued use of the drug can raise the risk of developing a psychotic disorder in later life, scientists said on Wednesday.

In a 10-year study of links between cannabis use and psychosis, Dutch researchers found that cannabis use almost doubled the risk of later psychotic symptoms.

Experts commenting on the results said the major challenge for health authorities was to deter enough young people from using cannabis so that rates of psychosis could be reduced.

"This study adds a further brick to the wall of evidence showing that use of traditional cannabis is a contributory cause of psychoses like schizophrenia," said Robin Murray of the Institute of Psychiatry at Kings College London, who was not involved in the research.

Wednesday's findings, published in the British Medical Journal, echo research last year which found that young people who smoke cannabis for six years or more are twice as likely to have psychotic episodes, hallucinations or delusions.

Cannabis is the most commonly used illicit drug in the world, particularly among adolescents, and is increasingly linked to added risks of developing mental illness.

But scientists say it is not yet clear whether the link between cannabis and psychosis is causal, or whether it is because people with psychosis use cannabis to self-medicate to calm their symptoms.

For this study, a team of Dutch researchers led by Jim van Os from Maastricht University studied a random sample of 1,923 adolescents and young adults aged 14 to 24 years.

The study took place in Germany and the researchers separated out anyone who said they were already using cannabis and excluded those with pre-existing psychotic symptoms so they could look at links between new cannabis use and psychosis.

They found that so-called "incident," or new, cannabis use almost doubled the risk of new psychotic symptoms, even after accounting for factors such as age, sex, socio-economic status, use of other drugs and other psychiatric problems.

They also found that in those who were already using cannabis at the start of the study, continued use increased the risk of persistent psychotic symptoms. There was no evidence for self-medication effects since psychotic symptoms did not predict later cannabis use, they said.

Peter Kinderman, a professor of clinical psychology at the University of Liverpool, said the study suggested authorities should take "a cautious and thoughtful approach to cannabis legislation."

"It's important to remember that psychosis is a very complex bio-psycho-social phenomenon...but this important paper certainly reminds us that there's a strong link to the use of cannabis," he said in an emailed comment.

(Editing by Mark Trevelyan)

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Comments (4)
eNLogic wrote:
I think this study proves that people who have had psychotic episodes tend to have experience with cannabis. However it does not prove that cannabis use increases the chance that someone will become psychotic. It even says that people who are already use cannabis were separated and those with pre-existing psychotic conditions were excluded from the study. How can you exclude that group? It would completely throw off the results.

Mar 02, 2011 3:27pm EST  --  Report as abuse
wzgru22 wrote:
I normally don’t comment on news stories, but this one begs some attention. While the scientific facts presented here do indeed lead one to draw a cause-effect link between cannabis use and psychosis, the two are not linked in a cause-effect manner, but they rather co-arise. What this means is that those who use cannabis may or may not already have a latent (subconscious) pre-disposition to psychosis, but those who *do* have a predisposition to psychosis will be more likely to use cannabis as a means for “coping”, and are therefore more likely to use cannabis more regularly, and for a longer period of time.

Because of this, because users who have a latent pre-disposition for psychosis will use the drug more regularly and longer, and because those without a tendency towards psychosis (i.e. more balanced people) will likely use the drug less frequently, and not as long, this study is based on somewhat biased evidence and the conclusion drawn is misleading.

As mentioned in the study, cannabis users may show an almost double risk of psychosis, but not because they are using cannabis, but because they are using cannabis to cope with already-emergent psychotic symptoms. The drug is not the cause of this problem. We as a society need to look at the environmental causes, as well as personal causes which bring a person to a state of mental agitation and discomfort–and, in addition, we should work to apply any of the many, proven successful lifestyle or mental/relaxation techniques anyone can find by a little web research.

Understanding the root cause of these problems and working to educate youth around these issues will help solve this problem, not blaming a drug or other coincidental factor.


Mar 02, 2011 3:28pm EST  --  Report as abuse
Sinbad1 wrote:
I live near a hippy town and there is lots of pot available. What I found amazing when I first moved here was the way children would attempt to buy or beg cigarettes from adults to mix with their pot.
Tobacco is legal for adults but not children so they couldn’t go to the store and buy their own.
Pot being illegal was much easier for the kids to buy.
Legalize it regulate it tax it and save our children.

Mar 02, 2011 6:52pm EST  --  Report as abuse
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