Large study finds link between cannabis use in teens and psychosis later

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.

"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...

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.

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.

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?

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.

Part of the issue with legal weed is it's much like if all alcohol was sold as minorly different varieties of Everclear at 150+ ABV, and brands primary boast was just how potent and alcoholic their mix is. It doesn't encourage appropriate usage and IIRC many of these cases of psychosis are from consuming high THC products 24/7 for weeks/months/years on end.

If anyone is curious, check out brands like Rove, Dompen, Care By Design, which offer THC pens at very low dosage. They're frustratingly undermarketed and understocked, but as a CA resident I buy and use pens that are ~4% THC (rather than 90%+). A single puff occasionally after the kids go to sleep - the effect is marginally psychoactive, scratches the itch for "relaxation without impairment", helps me sleep restfully.

Completely different experience to high THC products. If you compare the literal amount of THC consumed, it's an almost 20x reduction. It's literally the equivalent to having a half glass of wine instead of lining up 10 shots.

In my teens/20s, I would have advocated for legalization of marijuana and thought any argument against it was some antiquated, puritanical nonsense.

In the decade+ since, there's no way I'd do so.

I know three personal friends that are long time (allegedly not addicted) heavy marijuana users that all suffer from Cannabinoid hyperemesis syndrome to the extent that it's effected their daily lives substantially.

Two of the aforementioned are roughly my age, and are half as bright as they were as teens. Neither of them can follow a train of thought particularly well and are difficult to hold conversations with.

How much of this is attributable to how much more powerful "modern" strains (or whatever the geo-engineered differences are) is unknown, but I can't imagine it's not a factor. This is not the dopey "get stoned and play XBox and eat a whole pizza" stuff we had in the 00s.

I'm sure there's plenty of counterexamples or something, but my perspective on this has completely changed, influenced by examples like this.

Here's a study that somewhat contradicts this finding:

"Study: Older Cannabis Users Have Larger Brains, Better Cognition" https://news.ycombinator.com/item?id=46895950

How to manage cognitive dissonance on this? How to avoid counterproductive black-and-white thinking?

How to assess the relative strength of evidence of two or more scholarly articles about cannabis?

What did they control for? Were they randomly assigned to treatment groups? Was it a triple-blind RCT: Randomized Controlled Trial? Which groups were masked?

Does years of irrational persecution for cannabis compound to debilitating psychosis which indicates?

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.

From the article: "Teens who reported using cannabis had twice the risk of developing two serious mental illnesses: bipolar, which manifests as alternating episodes of depression and mania, and psychotic disorders, such as schizophrenia which involve a break with reality."

That 2X factor is big. If it was something like 10% - 20%, it might be noise or some other factor, but that big a number is real.

4000 out of 460000, that's about 0.8% or so? At the face of it, it doesn't seem a lot higher than the 3% lifetime risk of psychosis and whatever it is for bipolar disorder.

To me it doesn't seem like they control much for confounding factors, or the possibility that young people who might develop psychiatric illness could also be more drug seeking or irresponsible in their drug use.

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.

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

Since when does NPR use generic buzzy words like "huge" in their title ?

I always see whenever a study mentions risks of cannabis, it's always met with "it only happens to those with innate tendencies" but then I ask them do they even understand what those effects are? Do we understand what schizophrenia and psychosis is, it's exact mechanisms?

Western medicine can't even explain any of these ailments, where it comes from, how it happens, what triggers it but so many cannabis users shield and attack any new research or study that questions the risks of cannabis for the young.

If it truly is harmless then are those same people suggesting that they light up a joint with their children ? Doctors hand out edibles when they catch a cold or can't sleep?

While I do think there are deeply helpful properties of cannabis we are still early, new research is only beginning to come out as it gets scrutiny. It took us many decades to learn the harmful effects of tobacco while for a long time everybody just shrugged it off as conspiracy. It took heavy lobbying from those that stood to gain most to delay the truth of the product they were selling and a lot more political will from the other side to warn the public.

Right now what worries me is the marriage of profiteering and political ideology that have neutralized the similar movement that existed around tobacco and alcohol in the Western hemisphere. Many see money to be made or their political statement that they will defend vigorously. The real risks that I see is raising the THC % content to extreme levels for chronic users who built a large tolerance through long term habitual use and claim they aren't addicted, proliferation of white/grey dispensaries that make it even more accessible to the young. This really needs to be addressed when we don't even understand the mechanisms or can reliably explain the after effects of those risks coming to fruition.

I think this is a classic case of correlation does not imply causation. As someone that has known these people, and I does smoke as an adult, I would interpret that as people who are struggling with mental illness symptoms turn to weed as an outlet. Especially when we take it with the wider literature on drug abuse and mental illness any practitioner worth their salt knows mental illness makes drug abuse more likely and yes then the two affect one another which is why rehab is usually a big part of the hospitalization process. But what I don't want to see is more moral panic so we can renew the war on drugs which as always should really be the war on poverty and mental health issues.

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).

They do not compare to the baseline population correctly. Roughly 1% of all people are susceptible to schizophrenia, and up to around 4% schizophrenia, extreme bipolar, and other conditions that can result in psychotic episodes or extreme outcomes.

Drug use among vulnerable populations increases the risk of psychotic episodes, but does not increase the risk of developing those conditions. There is no difference in the rate of extreme psychological outcomes among drug users and non-drug users, and in fact, this study reinforces that observation - only 4,000 of 460,000 had those negative outcomes. Over the next 20 years, it's extrmeely likely that another 600-1000 will develop schizophrenia, even abstaining from drugs entirely. Drug use can trigger a psychotic episode and result in long term schizophrenia; by the time you turn 45, however, your odds of a schizophrenic break drop to almost 0.

The worst part of drug use and mental health outcomes is that it can rob people of normal years of life, and rarely, result in schizophrenic or other psychotic conditions being triggered when they might never have been. However, this is not just marijuana or other illegal drugs, but alcohol, caffeine, trauma or intense stress, and even chronic health issues can have the same outcome.

This study also fails to account for the confounding fact that people with mental health issues often pursue mind altering drugs in order to self medicate. People with bad conditions in life, especially younger, undergo extreme stress and are exposed to illicit substances much more readily than those in otherwise stable and healthy conditions.

The results and methodology are flawed, and the conclusions being drawn have little to no relationship with reality.

It comes down to susceptibility - genetics and health conditions play into this. Consult a doctor, and if you have risk factors, live your life accordingly.

If you don't have risk factors for schizophrenia, drug use will not suddenly put you at risk of developing it. Marijuana or other recreational drug use will not cause you to have a psychotic episode. If you do have risk factors, then you're twice as likely to have an episode by using drugs or experiencing other triggers than otherwise.

For those who are susceptible, your relative risk of psychotic episodes and mental breakdown double under mairjuana and other substance use.

For those who are not susceptible, your absolute risk of psychotic episodes and mental breakdown remain near 0. Drugs don't induce these conditions (except in the case of extreme stimulant abuse, and possibly extreme psychedelics outcomes, although getting fried by psychedelics isn't really the same thing as psychosis. Lots of high function deadheads survived some truly harrowing levels of substance use and are best characterized as "weird".)

It'd be nice if the media could distinguish between relative and absolute risk rates and communicate the difference effectively. It'd be even nicer if researchers and publishers didn't chase clickbaity results like this and mischaracterize things like relative and absolute risk for profit.

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