Smirnoff shits?

So about every weekend lately I’ve been able to kill a fifth of Absolut vodka with minimal repercussions. I am careful to eat and hydrate whenever I’m drinking, no matter what I’m drinking.

But man, Smirnoff vodka gives me diarrhea the next morning without fail. Doesn’t matter if I drink water, eat beforehand, or do anything else you’re supposed to do to mitigate hangover or damage. It tastes pretty much like Absolut, so why does this happen? Smirnoff is a little cheaper so it sucks that it has this effect. Does anyone else experience this??