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Adolescent cannabis use and later development of schizophrenia (wiley.com)
43 points by DanBC 14 days ago | hide | past | favorite | 51 comments

Why is it so hard for many HN readers to consider that cannabis might cause schizophrenia? There are tons of studies demonstrating a correlation, so it's not impossible that there is a causation too.

> Why is it so hard for many HN readers to consider that cannabis might cause schizophrenia? There are tons of studies demonstrating a correlation, so it's not impossible that there is a causation too.

If you went to school in the United States in the 1980's or 90's, you were lectured consistently and repeatedly by teachers, parents, medical professionals and police offices about the horrendous dangers of marijuana. The basic storyline was something like: if you took a puff of marijuana you would quickly degenerate into a slobbering drug addict and end up fellating some crack dealer for a $5 rock, after which you'd contract AIDS and die an agonizing death. So over the years, the folks doing the anti-cannabis messaging lost a lot of credibility, which is why folks are rightly skeptical of new anti-cannabis claims.

Note: There's a little hyperbole in here, but only a little. U.S. drug education was pretty bonkers in the 80's and 90's.

1. Many years of anti-cannabis propaganda and the war on drugs, despite never really studying the effects of cannabis, makes people skeptical of research like this.

2. This article in no way states that cannabis usage causes schizophrenia. It says there is a correlation, and furthermore the fact that both low and high usage having the same effects. That actually harms the case that it DOES, since you would expect the odds of it causing issues would increase with amount ingested.

> That actually harms the case that it DOES, since you would expect the odds of it causing issues would increase with amount ingested.

Not necessarily? The correlation is observed, and there may be causation, in one, or both, directions, that is all we can conclude from the study. The causality doesn't have to be linear with the amount ingested, few things are linear in biology. For example, one could imagine that a certain amount blocks the development of a particular region of the brain. Ingesting more does not necessarily blocks it "more".

There is no evidence that this happens, but it is worth exploring, because schizophrenia is a hell of a condition, and is still largely misunderstood.

This sounds like anti-vaxx talking point, government messaging and scientific research on the subject are two different things.

I'm not sure how this relates to anti-vaxx, which I am extremely anti-anti vaxx.

I'm saying we cannot interpret this research study the way people want to. Correlation != causation, and the results on this seem murky in general, as outlined how amount consumed does not affect likelihood of symptoms.

Comparing modern Covid research to this is... dishonest. We have a massive amount of data to parse and analyze with vaccine effectiveness etc.

Meanwhile, this is a single meta-study that doesn't make any strong claims.

> Why is it so hard for many HN readers to consider that cannabis might cause schizophrenia?

Currently, approximately 129M US adults have used cannabis and there are 3.2M schizophrenics in US. 16% of schizophrenics use cannabis, while 27% have a history of using cannabis. This makes any correlation, if there is one, extremely difficult to see, because currently, at best, only 864K schizophrenics of 3.2M have ever used cannabis. This means, if there is actually a causation, then using cannabis entails a risk of 1 in 149.3 of causing schizophrenia, which seems high until you consider schizophrenia affects 1 in 300 people worldwide. So it is possible that using cannabis doubles risk of schizophrenia, but we wouldn't say it caused it. 100% of schizophrenics drink water... why isn't drinking water researched as a cause of schizophrenia?

These arguments are shoddy and you know that. If it was so difficult to demonstrate a correlation then so many studies wouldn't have been able to do just that.

Not an argument, just answering the question.


> If it was so difficult to demonstrate a correlation then so many studies wouldn't have been able to do just that.

employs a fallacy, assuming the conclusion aka begging the question. But that's ok, because I'm really not arguing any position.

DARE and similar anti-drug propaganda lied through their teeth about the real consequences of using drugs. The war on drugs has been lost completely, but they continue to persecute low-level drug offenders when the distribution channels remain completely unaffected. The government (and by extension government-funded research) has proven itself unable to be trusted in this area.

Thank you, I feel much the same. It feels a bit like accepting the evidence if it agrees with your preconceived notions and reject the evidence if it doesn’t.

Is cannabis on the whole better than some other substances? Sure. Does that make it harmless and invalidate this paper? No.

By evidence you mean the correlation? Yeah you're right, also we should all become pirates to fight climate change, since there's an (inverse) correlation between amount of pirates and temperature

So do latent schozophrenics disproportionately seek out cannabis or does cannabis cause schizophrenia? Also, did these people start with cannabis, or did they start with tobacco and alcohol ?

Right, the fact that there's significant correlation between schizophrenia and cannabis use is well known, but I not aware that there's any decent evidence for or against causation. Schizophrenics have generally higher rates of substance use/abuse so a higher rate of cannabis use is not not odd, per se.

IIRC, there's also a very high correlation between schizophrenia and early substance abuse/overuse in general (such as high alcohol/caffeine use). Are these substances causal too?

It is, but also there is a thing called 'self-medication'*.

As we know, global warming has a positive corellation with a decline of a pirate activity, but nobody yet discovered the cause.

* as a person who at least read some things on it - it should be really described as 'attempts at s.m.' but here we are

there is casual evidence that alcohol and caffeine increase hospitalisations for schizos. With marihuana its a harder riddle, what is a cause of another, I guess you can ask the same about other substances and origin

My understanding is cannabis can trigger schizophrenia in those with a predisposition. Some people will have this triggered in their lifetime, and others will not. Some things like stress can trigger this, as well as some drugs like cannabis

> as well as some drugs like schizophrenia.

If someone offers you schizophrenia at a party, don't take it

Lol good catch, I was in a waiting room and didn't get to check grammar. Fixed

This makes sense.

Also it's known(both by researchers and users) that cannabis can increase/create paranoia in some people. And paranoia is stressful so that can lead to schizophrenia(and paranoia is a part of the diagnostic criteria for schizophrenia).

Anecdotal evidence, but I didnt seek marihuana, I actively avoided it, but had a crazy addict cousin who tried to force it on me for weird reasons. One time I was pretty drunked and tried it, got psychosis the next day finally ended in a psych ward. I am on meds till today

Smoking your first cannabis while drunk was indeed a bad idea! Hopefully the experience made you think about the abuse of alcohol and its consequences.

Please stick to the site guidelines and don't be unkind here.


bro, I was 17 at the time. Wasted the next 10 years living with schizophrenia. Smoke your weed but dont preach about alcohol abuse

The first is an interesting question, especially considering the potential length of the prodrome of some mental illnesses.

Would be incredibly hard to test though, requires going back and forth with a time machine. Would be cool, though.

isn't that like asking do latent diabetics seek out unhealthy foods?

No, because people with mental health issues like bipolar or schizo or even ADHD tend to self medicate with drugs before seeking help, if they ever do.

The full title is "Adolescent cannabis use and later development of schizophrenia: An updated systematic review of longitudinal studies"

They're not saying cannabis use cause schizophrenia. Their conclusion is pretty clear "Both high- and low-frequency marijuana usage were associated with a significantly increased risk of schizophrenia. The frequency of use among high- and low-frequency users is similar in both, demonstrating statistically significant increased risk in developing schizophrenia."

I feel schizophrenia is the wrong focus. To me that is having hallucinations and severe delusions. Don't know what the clinical indications are, using Twitter causes delusions as well.

But from my experience a solid form of psychosis is not too uncommon. We had an enormous amount of users in school and some destroyed their lives with weed and ended in psychiatric care or didn't finish their degrees. Another problem is that weed is extremely potent today. Not the same stuff people smoked in the 60s anymore. Today people use extremely potent cultivated plants.

I'm waiting for the day that these substances come in a bottle that has all the disclaimers from the controlled study in fine print at the bottom.

"may accelerate schizophrenia if you have a history of that in your family"

Then we can all move on and have it in the same substance of every much more dangerous OTC drug approved by the FDA.

I would like to see a study such as this one comparing the different strains of Cannabis and their respective THC/CBD %. I can't fathom schizophrenia developing from smoking high CBD weed.

You can’t fathom it? On what basis?

If you research "CBD affects on mental health" you'll probably come to the same conclusion. CBD attaches to the same CB-1 receptors as THC and can mitigate the anxiety inducing affects of high THC dosages.

The reason this is surprising is because THC is the psychoactive ingredient in weed.

CBD is mostly accepted as a milder agent, and has had medications containing it approved by the FDA, like EPIDIOLEX.

Can't be fathomed.

Been smoking weed for almost 10 years since I was 13.

I don't understand if the more I smoke the more risk I have to contract it? At this point I should be hallucinating forever...

Isn't there a very similar correlation for cigarettes?

I wonder if this is people with schizophrenia unintentionally medicating themselves?

Getting toxoplasmosis from a cat may trigger it too. But would these folks eventually become symptomatic anyway?

Does the study take into account different strains? Also hash vs pollen vs weed?

I don't have access to the full text.

if someone has access please add to scihub

like most mental health issues. it's more than just chemicals...it's a learned pattern

What do you mean by learned pattern?


What a bizarre take. Of all the mental illnesses, schizophrenia is one of the most severe, tragic, and random of them.

Even someone skeptical of broader mental health can watch a video of a schizophrenic person and see that there is something deeply wrong with that person.

I don't think you know what schizophrenia is.

>Bad parenting causes schizophrenia

Do you have a study or textbook that discusses this? I'm interested in reading more

They do not. It's an old myth - the society used to blame schizophrenia on bad parents, especially mothers. This has no grounds in medical research.

And now it is bad drugs.. AFAIK the argument against most environmental factors was that schizophrenia frequency seems similar globally after accounting for ways societies handle cases.

Given the ethical limitations on this kind of research, I think a research group that wants to talk about probable causation really needs a cross cultural method to randomly sample and demonstrate active case prevalence changes and to run that sampling over many years.

Quick google points to this: https://pubmed.ncbi.nlm.nih.gov/23800431/

It’s gotten “debunked” like so much else. Debunked means you aren’t allowed to talk about something. Bad parenting causes mental health problems, even though the factcheckers say otherwise.

This is the old, and silly, nature vs nurture debate. Its debunked because we now know that its a combination of genetics and environment (such bad parenting) that can bring about issues

Such that someone generally needs to have the genetic predisposition for <mental_health_issue> in order for the bad parenting to surface it. In some cases the genetic predisposition is stronger such that we need less (or more) environmental influence to being about <issue>

While it's not entirely incorrect to say that <environmental_factor> (such as parenting or cannabis) can bring about <issue>, its also misleading because we don't get the full picture of cause and effect And as such we have people who go around on the internet claiming they know the ~one true cause~ because they read some mischaracterized study reported on by <media_institution>

Never listen to media institutions about singular scientific studies, the reporting is almost always entirely trash

It's the old "Refrigerator mother theory" that's been largely discredited. Back from when autism was known as "childhood schizophrenia."


You could find textbooks from the 50's maybe. It's been discredited for a long time.

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