By the way, labeling an undesirable group with "mental issues" has been done many times in the past, sometimes even with "good" intentions.
A well-designed study may be more revealing, but the individual experiences are legitimate and should not be discarded solely because studies are possible.
A strong enough signal will show in a sample of one.
With a correct model, cause and effect can be predicted without any samples (scientific progress often occurs this way).
And some people’s intuitions are remarkably astute. Albeit there are a lot of people who have incorrect intuitions and don’t know it.
A cannabis example would be strong paranoia after one sesh. More ingrained paranoia (qanon?) that I have seen linked to regular heavy usage doesn’t feel to me to be a stretch of the imagination.
Yes, I have acquaintances and friends with no psychological problems that smoke weed. Also the same but don’t smoke.
Yes, I have acquaintances and friends with “undiagnosed” psychological problems that smoke weed. Also the same but don’t smoke.
No, I am not a professional psychological specialist.
Yes, I have some experiences to be able to make intelligent “non-professional” judgements about psychological problems. My definition of a psychological problem is one where the problem is seriously negatively affecting ones life, and ones skills are not successfully mitigating or correcting the problem. Environmental issues have a part to play in that. My friends and acquaintances have a wide range of ages.
You seem to be fishing for something - perhaps you could have just made your point instead (with caveats).
Disclaimer: I don’t use any form of THC or CBD. No strong reasons against it, just not my thing. I certainly have nothing against those that want or need to take THC or CBD.