“we lack the crucial epidemiological evidence”
Lack of evidence, is not evidence. Such populations (exposed to high levels of cannabis) are markedly different in many respects. Accurate diagnosis and record keeping of psychotic events are very likely to be different across such cultures and sub-cultures. Hallucinations might be viewed as a feature, rather than a bug, to people seeking them, or in shamanic cultures -therefor not diligently reported to the authorities. Violent or destructive behavior from psychotic breaks might be recorded and treated as simple crime.
An epidemiological study is a very academic and abstract method of looking for effects, full of complex confounding factors, especially when direct biological models are easily available (although possible ethically riskier or more difficult for a non-medical academic, better suited to just library research).
Dopamine modulation can very reliably be shown to produce psychotic episodes in vulnerable individuals - just get a borderline psychotic and give them a hundred doses of THC in an extract oil - predictable and repeatable results - they will be tripping.
Give a less susceptible individual a thousand or 10,000 doses. They will also hallucinate profoundly. Seeing and hearing things that are not there is the very definition of psychosis. They would not be diagnosed as psychotics for epidemiological record keeping however, because the condition was induced, and not innate. They would pass a psychological evaluation easily, after the drugs wear off.
So the big revelation here is that marijuana is temporarily mind-altering? This is a no-sh**-Sherlock observation, and very different than the Reefer Madness hysteria on this thread.
It is when marijuana use increases as markedly as it has in many Western nations with no corresponding increase in psychosis, which said nations have been well equipped to measure.
An epidemiological study is a very academic and abstract method of looking for effects, full of complex confounding factors
So what confounding factor cancelled out the increase in psychosis due to increased marijuana use?