Mega Drain inflicts damage, and 50% of the damage dealt to the target is restored to the user. The amount of HP recovered is rounded down unless Mega Drain deals only 1 HP of damage. In this case, 1 HP would be restored to the user. If Mega Drain breaks a substitute, no HP will be restored to the user. If the target has Liquid Ooze, the user will lose the amount of HP it would have gained instead.