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Comment by Daviey | Hacker News Reader

This study is published in the Lancet ( https://www.thelancet.com/journals/lanpsy/article/PIIS2215-0... ).

My interpretation of their findings is that it doesn't provide safe assertions that Cannabis is the cause or the effect.

Or in other words, does Cannabis usage create psychosis or do people with psychosis choose to use Cannabis?

Similarly, there are unknowns with mental illness and tobacco smoking. Some think that those with mental illness are more likely to smoke as self-medication.

http://ash.org.uk/download/smoking-and-mental-health-2/

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Exactly. It just basically says, from the people who requested mental health care, more of them used cannabis than from the control group. Great. They also present higher rates of smoking, alcohol use, self harm, obesity, and various disabilities. Some may be cause, some consequence, some none of them. The title is correct, there is a link, but that link has not established causality of any kind. This is basically repeating uncountable studies saying the same thing.

CBD, present in cannabis, is known to be antipsychotic, so the self-medication hypothesis is pretty strong. It's the same case as nicotine, schizophrenics have way higher rates of smoking, only because nicotine has a mild antipsychotic effect, not because smoking turns people crazy.

I'm saddened to read a plea for more causality (a topic that should definitely be more popular in all social and scientific claims), followed by personal and very unproven opinions, presented as tangible hypotheses.

I have not read the study so I can’t confirm that this one does not establish causality, but how are studies that don’t establish causality still published? At least shouldn’t they be appropriately labeled? We get some much pop sci drama from misinterpreting papers like that, it seems like it should be standard practice to show whether strong causality was or was not found/proven.

Paranoia from weed is a well-known phenomenon among smokers, and was so even long before clinical discussions about the effect became common. I'm surprised how defensive some (usually liberal-leaning) people become when the connection is suggested. I guess they have limited experience with cannabis, or they feel the need to protect a certain narrative.

Or they like good science that doesn't attribute causality without evidence? "Cannabis use increases the chance of psychosis" is just one of the three potential relationships. The other two are "The chance of psychosis increases cannabis use" and "A third factor increases both the use of cannabis and the chance of psychosis".

In reality, the effect is probably not just one, but some mixture of all three. It is extremely likely that people are self-medicating against psychosis with cannabis, that cannabis can increase the risk of psychosis in some people, and that the risk of psychosis is usually co-morbid with other mental health issues for which people also self medicating.

A study like this does nothing to help us understand the link, but yet the Authors seem willing to make strong claims about that link:

> The researchers suggested that if high potency cannabis was no longer available, the incidence of psychosis in Amsterdam would be expected to halve from 37.9 to 18.8 per 100,000 people per year, while in London, it would fall from 45.7 to 31.9 per 100,000 people per year.

That is irresponsible and bad science. It should be called out as such.

The article does mention that they studied subjects who had their "first episode of psychosis". You could still argue a person predisposed to psychosis can become a cannabis user as self-treatment even before their first episode happens, but that would be a stretch unless explicitly proven true.

Childhood trauma is also a predictor of psychosis.

And cannabis is a pretty good tool to help alleviate the symptoms of (though not cure) trauma.

Similarly, people who do illegal drugs and end up committing suicide. Some people point at that and say things like "damn, those drugs made them commit suicide!", when, more likely, they were self-medicating a mental situation that made them more likely to commit suicide in the first place.

I don't see what makes this scenario "more likely". You're still confusing correlation with causation but just using another cause.

Fair point, I should've left off the conjecture in the second part of my comment. I was trying to illustrate the point but, indeed, it did propose a cause where there's nothing beyond my own anecdata to back it up.

It's very hard to draw conclusions about causality from these sorts of a posteriori studies. That is, as you say, does cannabis cause psychosis, or do people with psychosis self-medicate with cannabis?

In order to get at that, you'd need to identify people with and without psychosis, and then follow them for many years. See who was more likely to use cannabis. And see whether using cannabis worsened psychosis. Not an easy thing.

No, it is impossible to draw conclusions about causality from such statistics only studies. The only way to establish causality is a randomized experimental intervention.

The sort of study you describe can distinguish to some extent between "A causes B" and "B causes A" but can't tell them apart from "C causes A and B"

I was going to make that point too, but the idea of randomly providing cannabis and placebo was too implausible.

They clearly stated in the "study" that they assumed (!) the causal relationship and then created their findings based on that. It is basically another science fiction paper for prohibitionists to use against people.

Flip side, purely personal anecdote.

I arrived in London with nothing from post Soviet block country.

I was burned out within 6 months.

Then I started partying and one friend introduced me to Cannabis, I started doing it every weekend and made it a point to stay away from it during the week, so it doesn't affect my work in anyway

I managed do lot better, make better connection, climb the corporate ladder faster and make a lot of money

Now, I've my own startup

Not all my friends have been this lucky with their Cannabis use

What I believe is that Cannabis has potential to unlock some capabilities of your mind. Wether it unlocks positives or negatives depends entirely on the person and can't be generalized.

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