I hear you can develop an immunity to the toxins, eating little bits over time would allow you to use it as a food source without it dehydrating you(via diarrhea/vomiting).
I wouldn't do it myself unless I was trapped in the wilderness somewhere with an excess, but there's some anecdotal information y'all can follow up on.
But yeah, had a lot around my parents property, about impossible to kill. One method that does work, but requires diligence and pretty much an entire summer, is chopping it off right below the soil w/ a machete. Repeat every time it sprouts back up, and eventually it runs out of energy without any leaves for photosynthesis. The other method that worked was digging it out, but if you miss even the tiniest section it'll be back next year.