Can you explain what exactly is unscientific about it, for those of us who haven't read the full study yet? From what I gather, this is about the age of onset

Can you explain what exactly is unscientific about it, for those of us who haven't read the full study yet? From what I gather, this is about the age of onset of psychosis in people genetically predisposed towards psychosis, ie. it's already accepted that the participants have a predisposition for psychosis. I suppose http://www.researchgate.net/profile/James_Maccabe/publication/259351867_Daily_Use_Especially_of_High-Potency_Cannabis_Drives_the_Earlier_Onset_of_Psychosis_in_Cannabis_Users/links/00b7d5357f7dbeb4ed000000.pdf http://www.researchgate.net/profile/James_Maccabe/publicatio... is the article; a quick search for the main author also shows e.g. http://www.sci-news.com/genetics/article00725.html http://www.sci-news.com/genetics/article00725.html regarding the genetics. Meta-reviews https://scholar.google.com/scholar?q=meta%20study%20psychosis%20cannabis https://scholar.google.com/scholar?q=meta%20study%20psychosi... seem to support it as well. ----- EDIT: reading the comments here, I feel I have to mention that yes, alcohol is also bad and possibly worse (definitely worse if you look at absolute numbers) and no, cannabis is not worse than heroin and no, we shouldn't ban everything that can do you harm. That still doesn't mean we should pretend cannabis can never do harm.