This sort of health hazard wasn't even on my radar, to be honest. It never would have occurred to me even to ask. Fortunately Google let me know when I was searching for something else that people also ask what happens if you eat hundreds and hundreds of M&Ms. Now you know, too. Spread the word.
M&Ms: Not Even 440.
Update: Yikes! It's even worse than I thought. I followed the link, and it says "3 or 4 of them will put you in the hospital."