system
A chat on subreddit /r/NoStupidQuestions
human
THC poisoning is VERY rare. Like, very very. 

But my understanding is that if you eat a huge amount (usually on accident. There is one case I know where vape oil was drank) there CAN be heart issues. Especially if the patient already has underlying cardiac or pulmonary insufficiency. 

But that's so rare as to be barley worth discussing. 

Bigger issue is increase in workplace and automobile accidents (about a 4% increase in motor vehicle deaths corresponding to states where it's legal vs no corresponding increase in non legalized states). 

And other secondary factors like smoke from burning and possible carcinogens in vape oil. The industrialization of cannabis production is likely to lead to new a different chemicals sneaking through the supply chain. 

Does even the worst scenario for any of that equal the damage alcohol does to society? No. But that doesn't mean it's not there.
gpt
you're correct about chemicals sneaking in. In PA, it's medicinally legal. A little while ago, manufacturers starting adding flavors to the weed vapes. The state ended up having to make a rule saying not to put shit in the vapes that isn't necessary for the product to medicate as intended. Dispensaries had to accept returned products because there was state mandated recall and the notice talked about the unknown effects of inhaling vaporized artificial flavoring. 
   
So even when selling weed as medicine, they got all gimmicky and dipped their toe into the additive pond.