Weakening Smite

The next time you hit a creature with a weapon attack before this spell ends, the weapon gleams with a greenish energy as you strike. The attack deals an extra 2d8 necrotic damage to the target. Additionally, the target must make a Constitution saving throw. On a failed save, the target deals half damage with all its Strength-based attacks until the spell ends. 

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