You use the connection briefly formed by the target’s cast spell to absorb a portion of the target’s life force. The target must make a Charisma save, taking 5d8 necrotic damage on a failure or half as much damage on a success. You heal an amount of hit points equal to half the damage dealt by this spell, rounded down. If this amount is larger than your current missing hit points, you gain an amount of temporary hit points equal to the difference. 

At Higher Levels: When you cast this spell using a spell slot of 4th level or higher, its damage increases by 1d8 for each slot level above 3rd.