There seems to be a correlation between long-term marijuana-smokers and the minuscule odds of various forms of psychosis. This equivocal finding is reported by Fox News thus:
Even Infrequent Use of Marijuana Increases Risk of Psychosis by 40 Percent.
Well, what did you expect? The caveats:
The researchers said they couldn't prove that marijuana use itself increases the risk of psychosis, a category of several disorders with schizophrenia being the most commonly known.
There could be something else about marijuana users, "like their tendency to use other drugs or certain personality traits, that could be causing the psychoses," Zammit said...
The overall risk remains very low...
My emphases. In a country of 60 million people,
the researchers estimate that about 800 new cases of psychosis could be prevented by reducing marijuana use.
Now think of the potential risks of drinking alcohol or smoking tobacco. How many lives would be saved from cyrrhosis or lung cancer if drinking or smoking were reduced? Infinitely more. So even if this study proves what it wants to prove, it seems to me to be a trivial point. Yes, we should examine all the evidence for benefit and harm before using any substance. But this is not the impulse behind some of the "experts":
"We've reached the end of the road with these kinds of studies," said Dr. Robin Murray of King's College, who had no role in the Lancet study. "Experts are now agreed on the connection between cannabis and psychoses. What we need now is for 14-year-olds to know it."
Yes: no fourteen year olds should be smoking pot. But who is arguing for that? And we find this:
Two of the authors of the study were invited experts on the Advisory Council on the Misuse of Drugs Cannabis Review in 2005. Several authors reported being paid to attend drug company-sponsored meetings related to marijuana, and one received consulting fees from companies that make antipsychotic medications.