I can tell you from years of first hand experience, it certainly makes you far dumber. The biggest factor is loss of memory. Most stoners (myself included) have terrible memory. I used to have near photographic memory, where I’d only have to read things once to remember them nearly verbatim for months after. I genuinely wonder at times where I’d be in my life if I had never got sucked into it years ago. I’m doing great despite the problems it’s caused me, but who knows where I’d be without it.
To be fair, over the past year I've scaled my cannabis use way back and my memory is definitely better. But only like 30% better, which is nice but not a night and day difference. (Memory issues were not why I stopped.)
On the other hand, there's a certain creative groove that's a lot harder to get into now. So there's a tradeoff.
Just one guess, but a lot of memory formation happens during various sleep cycle(s). Persistent cannabis use is commonly associated with lack of dreaming, which suggests it interferes with normal sleep cycles.
I was experiencing lack of dreaming after some time of daily use, and was able to regain my ability to consistently dream (and remember them) by simply ceasing cannabis use by 5pm each day. I don't experience noticeable problems with memory, but YMMV.
A few of my friends are chronic users and have a characteristic that when talking to them even when not high, there is a noticeable pause. It's like when they do those news interviews from someone around the world via satellite. There is the question and then a pause while the person just stares blankly for second, then recognition of the question and the answer. Have you ever experienced this yourself or notice it in heavy users.
As a chronic user, this is something I experience while stoned, but not while sober. I have a lot of behaviors when sober that people tend to classify as ADHD-like and I suspect it is related to this pause. Normally, when sober, I have a tough time staying focused on one thing. I typically have many projects going at once - half of them forgotten. You should see me cleaning my house - the whole thing will look torn apart as I jump from one area to the next, until the very end.
But when stoned, during that pause, I'm finishing with processing another thought that is already in my head. I find it harder to context-switch immediately when stoned. This is very different from my normal experience when sober, where my brain is very "flighty." The other time I notice this type of pause is when I've entered a "flow state," e.g. when deep in a programming project.
Sometimes I can leverage this "focus" into productivity when stoned, but then I am often equally likely to get focused on the wrong thing.
That said, it's well established that marijuana use acutely reduces your reaction time.
> you are witnessing the practice of thinking about the consequences of words before commiting to speech.
It feels different than that though. Its not unusual for someone to take beat before responding, but in that case there are facial and body cues that they heard you and are just getting their thoughts and words in order. But in the case of users, there is an expressionless pause even before that. More like blank pause, then facial cues of thinking, then an answer. That's why I used the 'via satellite' analogy because its like it takes longer for them to even register that they have been spoken to.
But maybe its a pop-science kind of fact that I've been carring along all this time without factuality?