What a strange study. Only less than 1% even developed these conditions.

They excluded people with a mental health diagnosis, and their data for already having symptoms was having a diagnosis?

Why do they assume this shows marihuana causes mental disorders, as opposed to being undiagnosed whilst already showing symptoms leads to self medication, for example?

I’m sorry, but most psychology research is just so incredibly badly done.

"But by excluding teens who were already showing mental health symptoms, the new study points to a potential causal link between cannabis use and later mental health diagnoses. Additional research is needed to understand the link fully."

Hm, but this does not exclude the possibility that the being prone to mental illness comes with a little bit higher tendency to consume cannabis...

Unless you blind this, I’m not sure it’s possible to get past the correlation or causation problem. Weed use is not yet so destigmatized for teens that usage itself is not a marker of deviance (in the math sense, not any kind of judgement).

I used to read forums for schizophrenics (self disorders fascinate me, look the term up if you want to understand schizophrenia), and it was the consensus there that out of all the recreational drugs cannabis caused the greatest deterioration in one's mental state. Those are generally fairly sick people, but I don't think one can just ignore this signal. I personally went catatonic once after consumption, and I'm not schizophrenic at all. And that was in Amsterdam, so it wasn't some trash spiced up by a 17-years old dealer with whatever he found in his grandma's medical cabinet.

The NPR article seems to confuse causation and correlation.

The actual paper doesn't, and merely implies correlation. Which is fascinating (and well-known) and might still prove useful in one way or another.

[1] https://jamanetwork.com/journals/jama-health-forum/fullartic...

The correlation used to cite heavy (daily repeated administration across the day; what the kids call "the chronic.") But now its just any degree of use.

I should add that I happen to know of more than one heavy user who subsequently progressed to Schizophrenia or bipolar disorders so I don't personally doubt the cause and effect.

But this blanket correlation seems to me to be overbroad.

Marijuana legalization arguments were my first introduction to motivated reasoning. I was pretty inclined to agree that locking up non-violent drug offenders was a net-harm to society. But, the pro-legalization folks would argue patently crazy things: it cures cancer, the smoke isn't bad for you at all, there are no downsides! etc.

It seemed obvious to me that you could make a more realistic argument and just stick to an argument which states that due to drunk driving and domestic abuse, marijuana is less harmful overall than alcohol, but is treated as more dangerous. (and yes, the other side was a bit crazy too. "When you buy weed you're supporting the same terrorism that happened on 9/11")

Later research (such as this) has suggested a link between marijuana and psychosis, however the actual risk factors do seem difficult to nail down. (however, this is still a far cry from the claim that it's totally harmless)

What I ultimately learned is that in a pitched political battle, people actually damage their credibility because they're afraid to cede _any_ ground to the opposition, even when that means making unrealistic claims. A centrist (or just someone who is undecided) is not really taken in as much by these extremist argument, and to their eyes it damages the credibility of one or both sides.

As well as the correlation/causation problem...

From what I hear, cannabis on sale today is rather stronger than when I was young. That sounds bad to me. Curiously I see this as a pro-legalization arguement, if it were available in a shop I could select a mild flavour, rather than the skunk that the criminals grew, and is all that is on offer

I’m in two minds about this, on the one hand I spent a week with acute psychosis after smoking weed when I was a teenager, so I really think people have to be more aware of the risks. On the other hand, I think it’s clear that this is not a perfect research design, and there are obvious possible confounds.

What about legalisation as a natural experiment? Has anyone done diff-in-diffs of US states and simply looked at eg mental health diagnoses or hospital admissions?

For what's it worth for an N=1 study I watched a relative's young family fall apart because of cannabis induced psychosis. They had two young kids, husband was smoking pot recreationally (not sure how long he was doing that) but at some point he started hearing aliens talking to him from the cracks in the wall. Naturally you can't just keep doing all the regular life and family stuff when you have more pressing issues like visitors from out of space in the walls talking about attacking earth.

I am not saying anyone should or should not use these substances, but that was enough of a lesson for me to know never to touch that stuff.

So just for context

"Based on data from 2023–2025, approximately 15% to 17% of American adults currently consume cannabis." - Gallup

So though this may be technically true in some sense, it should also be understood that if cannabis had any major immediate drastic effects we would have noticed them decades ago. Perhaps weed, like alcohol, needs a legal minimum age of 21.

Not a skeptic, but I've seen these studies for a while. Do we have any idea what the mechanism could be?