>When the wielder is poisoned (regardless of whether it is regular or badly poisoned), it heals 1/8th of its maximum HP at the end of each turn, and is immune to poison damage. If the wielder is under the effect of Heal Block, it does not gain HP at the end of the turn. If the wielder loses Poison Heal, the Toxic damage it receives at the end of the turn is the same as it would be getting on that turn if it hadn't had Poison Heal.
-Smogon