> I thought it was well-known that marijuana use among adolescents was a risk factor for schizophrenia.
Incorrect. Those predisposed to schizophrenic and some other mental disorders are more likely to have those symptoms aggravated by chronic drug use. Pot doesn't create mental illness, it exacerbates it.
The lesson here is not to smoke weed in your developing teen years, or to experiment in a safe environment if there is a history of schizophrenia in your family, something that should be a no-brainer.
"Safe" is a very relative word and a substance can only be as safe as the person consuming it. Incorrect safety procedure when ingesting a substance, such as taking drugs without proper dosage experimentation or in unstable environments, should not be held against the substance itself.