For The Love of LoL.. Please Remove Corrupting Potion From The Game
Healing potions shouldn't give additional damage, especially not on-hit DoT damage. Red Elixir was removed because it was too strong early and corrupting potion is not any different. It's completely busted on any bruiser or tank early into the game and it's simply unfair to have to lane against. The amount of sustain the potion adds is far more than any Doran's item can currently provide (and you only get 1 potion with a Doran's item) and the damage from proc'ing the potion's passive effect is just as strong.
Seriously, either majorly buff the other starting items to compensate or remove this potion. You shouldn't have to counter someone starting with a corrupting potion by buying another corrupting potion.. but right now in a lot of cases that's literally the only answer unless the other person is terrible, countered, or you have a decent amount of help.
Let's not even get started on champions like Singed abusing secret stash with 2-3 early Dark Seals so that he heals faster than Jesus himself with CP. Welcome to League of Potions.