Isn't it established since about 25 years that any drug-use can bring onset of schizophrenia in those vulnerable?
There's considerable debate about the causality.
Does psychosis cause people to smoke more cannabis? (It causes people to smoke more cigarettes).
Does cannabis cause people who would not have had psychosis otherwise to get it?
Or does cannabis just bring out an underlying psychosis that the person probably would have experienced anyway?
It's probably a bit complicated, with circular stuff going on.
While I'm strongly in favour of legalisation of all drugs I am a bit worried when some of the legalise crowd refuse to accept that there might be health risks. (I'm also frustrated when the anti crowd refuse to accept that the situation is probably a bit more complicated than "drugs make you mad")
https://pdfs.semanticscholar.org/f961/639e2a998d275f3e8f8f4c...
Leaving generic psychosis aside, when talking about schizophrenia this is a weird argument. Schizophrenia tends to worsen with every episode. It's of paramount importance to prevent any of them.
Having the first episode triggered by smoking cannabis with age 17 is worse than having the first episode brought on by a different cause with 25.
[Edit: I just realized I assumed causality here, which I have no proof for. But I do think that schizophrenic episodes are triggered by stressful thought-pattern and drug-use is one situation where those can occur.]
Concerning cannabis I'm mostly worried about the motivational problems it brings along (It seems to massively impair dopamine production in the brain). We are already a society to lazy to prevent it's own demise due to climate change.
If poor people are more likely to use drugs, and poor people also have a higher incidence of schizophrenia, you could arrive at this correlation even if marijuana and psychosis are entirely unrelated.
A quick Google search for "drug use by socioeconomic status" turns up a 2012 article titled "Socioeconomic Status and Substance Use Among Young Adults: A Comparison Across Constructs and Drugs" [0] which concludes, in part
> Findings based on three indicators of family background
> SES—income, wealth, and parental education—converged in
> describing unique patterns for smoking and for alcohol and
> marijuana use among young adults, although functional
> relationships across SES measures varied. Young adults with
> the highest family background SES were most prone to alcohol
> and marijuana use.
EDIT: Change lede.
Poor people are more likely to get caught for using drugs, however, simply because of living spaces. You and a couple friends wanna get high? Low income, you might be in a car, on the corner, or in an alley. Higher income, you might be in your basement or pretty private backyard.
What do potential health risks and legalization have to do with one another?
Ironically, that's only true when marijuana is illegal, hence a poor argument for legalization.
Legal substances may be easily purchased with minimal social interaction.
Mini anecdote: met a very friendly schizophrenic guy in a coffeeshop who got really paranoid and uncomfortable after he smoked... and apparently he smoked all the time.