It’s the journal of the American Medical Association, it’s a peer reviewed journal and it’s as reputable as scientific journals come. the author affiliations are listed at the top of the article if you click the dropdown:
There’s a real link between cannabis use and some mental illnesses, this isn’t the first paper to make that connection. What that connection is and whether cannabis use among children is causing mental illness is still AFAIK an open question. There are, according to my psychiatrist, conflicting data on whether cannabis makes depression worse or better. It seems to help for me, so I continue to use it with their supervision and advice, but I also know people who quit cannabis and felt better as a result, so I think if you use it and have one of these illnesses, it’s worth running your own trials to determine whether it’s helping or hurting.
I am aware. If I may refer you to the very next sentence: