If you want to spend a few depressing hours this afternoon, navigate to Wolfram Alpha and type in “LD50,” followed by the substance of your choice. LD50 is the lethal dose of a substance that would kill 50% of people that you gave it to, and it applies to everyday foods like caffeine just as much as it applies to doses of radioactive materials.
If you want the same kind of sobering facts, only in a bite-size (pun intended) form, watch this video from ASAP Science, This Much Will Kill You, which details the lethal doses of the stuff you keep in your larder.
It turns that if you eat or drink enough of it, then everything, even water, will kill you.
Lethal dose is measured as the amount of substance required per kilogram of the target creature. Wolfram Alpha’s data is drawn from studies on rats, not humans, for fairly obvious reasons. While it’s pretty nasty to get rats so hopped up on espresso that they die, doing the same thing to humans in the wrong state will land you with a lethal dose of your own.
To check the figures in the video, then, you can either follow the extensive list of references linked below the video on YouTube, or you can extrapolate from the rat data. It’s not perfect, but you’ll get a ballpark of what to stay away from. For example, the video claims that 70 cups of coffee would be the end for a 70 kilogram (154 pound) adult. Using the rat dose of 192 mg/kg, we get 13.44 grams of caffeine required to kill that 154 pound human. Wolfram Alfa also lists the “average” cup of coffee as containing 152 mg of caffeine. That comes out at 88 cups. So 70 cups isn’t that far off.
The rest of the numbers match up in the same kind of way, ballpark-wise, although the cherry-pit claim is a little off. The video says that two pits can kill you if you chew on them, but Snopes says that cherries aren’t nearly as dangerous as apricot or peach pits, and further research puts the fatal dose of even well-ground pits in the hundreds.
So, sit back, make a single cup of coffee, and spend a few minutes learning how the most mundane things can kill us, whilst marveling that the still-illegal-in-most-places drug cannabis is almost ridiculously benign, with even a dose 250,000 times the normal amount failing to kill you, according to the government in Oregon.