In case the title isn’t clear, are there any substances in which, when consumed in a moderate amount by themselves are harmless or nearly harmless to human health, but if consumed together (or if one is consumed today and another consumed tomorrow) can be fatal?
We’ll ink cap mushrooms and alcohol?
Neither one will kill you (although I’m not sure the ink cap would be great on its own) - but drink some alcohol slightly after and you can die.
Plenty of multiple drug interactions as well.
Also MAOI with favs beans, sauerkraut, chianti, and a bunch of other stuff with tyromine can cause a hypotensive(or hyper - don’t remember) crisis which you could theoretically die from.
Don’t mix bleach and ammonia.
Thanks – for some reason I didn’t think of drug interactions.
Vinegar and baking soda. 
Well, Carbon and Oxygen individually are harmless, but Carbon Dioxide can be poisonous and Carbon Monoxide is deadly.
'Cause each of these is totally harmless alone.
And yet, you’re breathing both at the same time, and it’s not doing a thing to you.
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Don’t mix bleach and ammonia.
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Bleach and ammonia are both plenty toxic on their own, and honestly the things you get by mixing them (chloroamine, mostly) aren’t markedly worse than the starting materials
Drug interactions, either with each other, with alcohol, or with food, are probably the best you’re going to get.
Melamine combined with cyanuric acid forms a structure that screws up your kidneys. I don’t think either is considered harmless alone though, but combined I believe they are worse than either ingredient alone.
I don’t have a copy, but Deadly Doses is the reference book you need for questions like this.
Gaseous hydrogen: Not particularly harmful.
Gaseous oxygen: Not particularly harmful, when inhaled in moderate doses. Required for animal life, in fact. Excessive doses could be caustic, however.
Combine the two in certain proportions, and you get (Gasp!) the deadly, ghastly Dihydrogen Monoxide!
Pop Rocks and soda.
I know it’s true. An urban legend told me so!
And maybe Mentos and Diet Coke?
Well, a roll of Mentos and a 3 liter Diet Coke definitely DO make a fantastic backyard geyser! That’s one of my son’s favorite “experiments.”
(That and creating bombs by putting dry ice iand warm water n a soda bottle.)
Potassium Permanganate and Glycerin.
Water, Sugar and Yeast. Produces C02, if the C02 is allowed to collect in a low depression and displace the oxygen it could suffocate.
Only after a certain, possibly devastating explosion.
It’s the gas that is produced when you mix them that is the additional danger that isn’t present when merely cleaning with bleach or ammonia by themselves. You can easily be working around either bleach or ammonia by themselves and not be in danger of passing out from the fumes. See post 11.
Alcohol combined with desperation has proven fatal, (and at the very least, has contributed to Coyote Love on many occasions).
Dihydrogen monoxide can cause fatal reactions when used improperly, too.
:eek:
The one I always think of is Tylenol with alcohol. More than a few people have done in their livers with this seemingly harmless combination.