Strength Sap lowers the target's Attack stat by one stage, then restores the user's HP by the same amount as the target's effective Attack stat before Strength Sap was used. The amount of HP restored depends on the Attack stat after applying stat stages.
The target's Attack stat is lowered even if the user of Strength Sap has full HP. If the target already has -6 Attack stat stages, Strength Sap fails; however, if the target of Strength Sap has +6 Attack stat stages and the Ability Contrary, Strength Sap will still restore HP. Strength Sap will still restore HP even if the target is protected by Mist or its Attack is not lowered due to an Ability such as Contrary or Hyper Cutter.
If the user is holding a Big Root, it recovers 30% more HP. If the target has the Ability Liquid Ooze, the user will lose the amount of HP it would have gained instead. Abilities like Huge Power and items like Thick Club do not affect the HP restored.
If powered up by a Grassium Z into Z-Strength Sap, the user's Defense stat rises one stage.