Drain Life

You channel a beam of energy from a creature within range to yourself. When cast, and at the end of every subsequent turn, the the creature must make a constitution saving throw or take 3d6 necrotic damage or half on a successful save. You regain hit points equal to the damage dealt. The spell ends when the creature succeeds the save three times. 

At Higher Levels: when you cast at this spell 3rd level or higher, the damage increases by 1d6 for each two levels above 3rd level.