I know this is 100% anecdotal, but a good friend of mine who was a brilliant programmer discovered cannabis in his late 20s after moving to the bay area for a well earned high-paying gig. Prior, to my knowledge, he didn't even drink alcohol. After about a year of extremely high dosages, something in him snapped. He just lost his mind. He became convinced the internet was sentient and was speaking through him and all kinds of other nonsense. He's been under psychiatric supervision near his family home back on the east coast ever since.
Again, it's anecdotal, and there could be a myriad of contributing factors - I know he had also begun drinking during that time period. But, until this happened, the idea of anyone going mad from cannabis was laughable to me. Now, I think about him sometimes when I'm visiting legal states and indulge myself in some quality edibles.