There's no evidence suggesting permanent brain damage to adults who use cannabis.
February 7, 2011
Cannabis May Influence Onset of Psychosis
Research to be published this summer finds that the use of cannabis is associated with the early onset of psychosis. Christie Nicholson reports.
This particular study found that marijuana use is associated with early development of psychosis.....
The evidence is mounting. No, the evidence is not mounting.
"Associated with" is not indicative of cause and effect. You see, a large percentage of illegal drug use is what might be called "self medication." EG, "I feel bad, so I'll take this stuff and I'll feel much, much better."
The self medication of someone with latent or emerging psychotic tendencies does not imply said tendencies erupt faster due to the self medication.
This is a difficult subject, by the way. It's one of those things that's ugly no matter which way you paint it or look at it or which action you prefer or suggest.