These ingredients don't sound much different than the corn syrup and phosphoric acid in carbonated sodas. Maybe I should have just bought a can of pop?
Additional acid contributes to irritation. So why doesn't the phosphoric acid irritate the stomach? At high concentrations, it's nasty stuff. The phosphoric acid in the syrup is very dilute, and it is not fully protonated (if the syrup has a pH of around 2.5-3, it's mostly H2PO4- with a smaller amount of H3PO4). The phosphoric acid has a pK1 of 7.5× 10-3) and so can buffer as H3PO4/H2PO4- around a pH of 2.1. The pH of normal stomach contents is typically lower than this (about 1.6 to 1.8). So the phosphoric acid in the syrup won't lower stomach pH by dissociating.
You might want to visit Quickcare's resource for more information about nausea prevention. They specifically suggest flat soda pop, non-acidic fruit juices, and popsicles as prevention for nausea!
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