Was it "A poisoned Pokemon" or "A badly poisoned Pokemon"?
There is a difference in that and I assume it's just a poisoned one.
I marked the difference.
A poisoned Pokémon will take damage equal to 1/16 of its maximum HP every turn, after it attacks, or at the end of the turn if it did not attack. If a poisoned Pokémon causes an opponent to faint, the poisoned Pokémon will not take damage that turn. Outside of battle, all poisoned Pokémon lose one HP for every four steps taken.
A badly poisoned Pokémon takes damage equal to 1/16 of its maximum HP on the first turn, after which damage increases by 1/16 each time it takes poison damage. When a badly poisoned Pokémon is affected by Haze, switches out, or when the battle ends, its poison status becomes regular poison.