Chubbyemu explains it best: https://inv.nadeko.net/watch?v=ifXH86-eIqk
But basically, the electrolyte balance that’s healthy for a horse is quite a lot higher than what is healthy for a human (due to body mass differences, among other things). The magnesium in the horse electrolyte is actually over the lethal dose for a human if taken as written. You could theoretically take it and be fine if you calculate the proper dose yourself, but by that point you’re better off just buying human products, I guess.
EDIT: I was thinking of manganese, not magnesium, but that’s 1500% of the daily intake, not necessarily lethal dose. Sodium, though, is over the lethal dose.
Gas leaks: