So smoking skunk cause psychosis, but milder cannabis doesn't?

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The Mail on Sunday has shouted that ‘cannabis TRIPLES psychosis risk’ and that skunk is to blame for ‘1 in 4 of all new serious mental disorders’. Is this what the study they cite shows? Well, no, but it’s really interesting research which could advance our understanding of the relationship between cannabis and psychosis.

The research compares a group of first-episode psychosis patients in South London with a group from the general population in the same area. Not only did the authors ask participants about the frequency of their cannabis use, but also about the type of cannabis they used– specifically whether it was skunk, or hash.

They found that those with psychosis were much more likely to have used skunk every day, than to have never used cannabis. Conversely, people who smoked hash every day were no more likely to have psychosis than people who never tried cannabis.

But does this mean cannabis triples psychosis risk? The headline reported in the Mail came from a ‘population attributable fraction’ that the paper calculated: the number of cases of psychosis that would be prevented if all skunk use was removed, assuming that cannabis causes psychosis. The authors of the study estimated this to be 24%. However, the authors clearly point out that they cannot be sure the association seen in their study is causal.

There’s lots of consistent evidence associating cannabis use with psychosis and schizophrenia, but as the saying goes, correlation isn’t causation. For all sorts of reasons, you can’t randomly assign one group of teenagers to use cannabis, and another not to. This means you have to observe what people choose to do, and the people who choose to smoke cannabis might be different in a variety of other ways, which could be the cause of the increase in psychosis risk. Although you can control for these in analyses, you can never be sure you’ve adequately adjusted for them.

This study uses a case-control design. This type of study can lead to bias if the control population is not adequately selected. In this article, the controls were selected from people who lived in the same area of London. However, the authors noted some difference between the cases and controls, in particular those with psychosis were more likely to be male, more likely to be white Caucasian, and more likely to be heavy smokers. Psychosis is more common in men, and more common in ethnic minorities (in particular those of migrant status). The authors accounted for these differences and adjusted for other potential confounders, but there could be others that weren’t measured.

Another drawback of case control studies is that the exposure measure (cannabis use) has to be assessed retrospectively. This can lead to biased findings if having psychosis might affect likelihood to over- or under- report former drug use. Given that an association was found with skunk but not hash, perhaps this is unlikely to be a problem, but again the authors can’t be sure.

For all the caveats though, this study is really important. It’s the first of its kind to try and separate out different cannabis potencies in this way

http://www.theguardian.com/science/sifting-the-evidence/2015/feb/16/does-smoking-skunk-cause-psychosis-but-milder-cannabis-doesnt

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Yeah I saw this. Confirms my anecdotal experience that skunk is associated with psychosis. But I think it is important to question:

  1. Is this psychosis acute or long term?
  2. Does stopping skunk still lead to psychosis?
  3. Is this psychosis in the form of schizophrenia?

I mean I know skunk can cause paranoia but how long does this last. I am glad the study differentiated between skunk and hashish and if I read the report correctly is says there is no correlation between hash use and psychosis? I think this is an important statement which has not been picked up by the British press. Namely hash is probably safer than skunk (although this is assuming the form of hash is not as strong as skunk I.e. Less the and possibly more cbd).

In my opinion this shows illegal skunk is dangerous and has way too much thc. If cannabis was legalised and formalised there would be safer strains available and people who have drug induced psychosis would likely (imo) have better, earlier access to mental health support. I read that the Netherlands has classified skunk with a thc content of 14% or higher as a class a drug. I think this is appropriate. But to insure this cannabis would have to be regulated.

My two cents worth.

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Thanks for the info. I smoked some kinds of hash. But I dont know if it was skunk, cannabis or weed. I would have a guess and say that i mainly smoked weed (because it was leafy in many cases). Where does this leave me in terms of relation to psyhcosis? My pshyciatrist told me that what ı had smoked caused my psychosis. So, I stopped having them nearly 10 years ago and I am determined not to have any of it again. All the best

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My current job in the lab at school is to butcher articles and call ■■■■■■■■ on them as specifically as possible while also addressing the validity of their findings. I see lots of flaws in this news paraphrasing of the findings of this study. I want to see the whole article, the real journal article, not what some journalist working for theguardian.com thinks and go at it with a pen and highlighter like I do every other piece of literature I read. Studies can be bullshitted in many ways. All it takes is a little bit of misleading statistics (huge sample size, for example), recruitment methods (who did they include in the study and where did they recruit them?) or leaving out some relevant information that would count as an independent variable or “factor” in the study (for example, leaving out what subjects did in a waiting room could have an impact on a study; I advised a master’s student to leave out the fact that subjects in a trauma study were instructed to read magazines in between sessions of speaking or writing about their traumas because reading an issue of “Guns & Ammo” before talking about how your father’s suicide by gunshot to the head would screw the study, but that is just a worse case scenario. He agreed to take it out and just say that the subjects waited in a waiting room), and studies can be flawed in many other ways. The master’s student’s thesis is good though, that was a minor flaw that can be quickly swept under the rug.

Say they recruit subjects and the sample size is 1k lower class white people, and half of them didn’t finish high school. They’re all uneducated lower class white people! NO EXTERNAL VALIDITY UGH GET THIS ■■■■ OUT OF MY FACE (the global population is not 7 billion stupid white people) and then I paraphrase my thoughts on the limitations of the study in a scholarly manner instead of calling it “■■■■■■■■”, but believe me, lots of studies are ■■■■■■■■.

I am actually good at this, I work with graduate students on their projects while I am currently reviewing literature for my thesis (previous research is referred to as literature, the literature review phase is hell, reading and taking detailed notes of about a dozen relevant studies is the first step after searching databases to find around 200 relevant studies. I have a huge stack of abstracts, about 80 social psychology abstracts and luckily only around 50 clinical abstracts, the social experiment got washed out so now I am down to around 50 references. My topic is very specific and a relatively original idea, I was told by the doctoral student who supervises me that I have hit a gold mine). Today I need to print out at least ten very similar studies to my proposed idea and master the material, I have to know everything that has been done, how it was done, and what was NOT done in a week.

I chose the chair of the Phi Kappa Phi chapter at my university (which I just joined) who got his PhD from Harvard to be my mentor because he won’t let ■■■■■■■■ get published by his students, period.

I would need to see the PDF of this study and actually go at it with my own hands in order to give it any sort of credit.

But come on, don’t smoke weed if you have a family history of schizophrenia OR if you have schizophrenia. The very smell of weed makes me feel sick, it is a ticket to a 12 hour visit to the deepest part of hell for me.

Mouse had spoken. Mouse needs to get on his work and quit writing essays on an online schizophrenia forum.

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LOL. I could probably spend less time on the forum and more time studying documentation for my engineering/consulting job too.

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@mortimermouse So are you saying only psychologists should comment on such things or maybe just those of us who are more intelligent than psychologists?

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well i just realised i hope. i actually realised it yesterday, but i thought it cant be. i think my cannabis use caused my psycosis or schizophrenia for 9 years now… iv’e smoked dominantly hash. dont remember the link between having or getting schizophernia for cannabis use. maybe its just psycosis. or maybe i have a schizo geen. i thought i was schizophrenic do . now i dont know. now i am depressed asswell maybe because of cannabis or just. deppressed after ■■■■■■■ upp my head after psycosis. dont ■■■■■■■ know anything now. i will read upon drug enduced psycosis and all that. dont need to Wright off topic

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i was normal before the first time i smoked. when i started smoking Things changed allot

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I’m merely saying that it takes a formal education in sciences to fully understand an empirical study. Knowledge of advanced statistics and research methodology.

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well i dont really know, if cannabis caused it. cant remember but i was pretty normal i think half a year to a year, after i started smoking. maybe its how much you smoke or whatever. cant remember so long ago. im gonna stop writing speculations

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i have been psycotic before,during and after i smoked cannabis. cant remember that something special happend. but one time i smoked black sticky oily hash wery god. then i got hearing hallucinations, smoked that couple times after that but it didnt happend again. thats the only time i can remember something like that happened

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To put it in simple terms it likely means you have to smoke more of milder canabis to reach the stage of psychosis than a stronger form.

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**Will we ever know for sure?
I agree with @mortimermouse, if there is a history of a mental disease-don`t do it.
However, I have a father who was diagnosed with borderline sz, and he is 81 years old and smokes it ( I have no idea what kind, but it smells terrible )…My ex quit when we were young because he said it was making him paranoid-but he has no MI.
My dad actually does better after a smoke.
As for my son–who has sz, he should not. But then he did meth and all kinds of other substances, had a predisposition, AND was in an accident that gave him a concussion-hit right at the frontal lobe and knocked unconscious.
There are too many variables… **

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All studies I’ve read on cannabis and psychosis run into this problem of the direction of causality, They find a correlation, but it can’t be said whether it is the cannabis causing the psychosis, or the yet-to-surface psychosis predisposing people to smoke more cannabis. I always wonder why they don’t test it on mice, just inject them with THC and see if they start to display psychotic behavior. Such studies don’t make it through the ethical comittees when it comes to humans obviously, but for mice it seems acceptable. It might sound weird, psychotic behavior in mice, but for studies of antipsychotics they have standards for what constitutes psychotic behavior in mice, they induce it with some substance and then administer the antipsychotic to see if it helps in earlier stages of testing. Maybe such studies are around and I just haven’t read them.

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In a lot of cases marijuana is the straw that breaks the camels back and leaves some helplessly psychotic when they would have remained normal had they not been smoking.

My life would be totally different if I had never smoked weed. In both good and bad ways.