You reach out and whisper under your breath a secret word or phrase as you tap the food or drink you wish to poison. When you do you must roll a stealth check to whisper silently enough and a sleigh of hand check to move quickly enough to avoid detection, or distract the target enough to do so. Once you tap the item that will be poisoned it will look as if it hadn't been touched at all. If you are detected the target will get to roll an investigation check to detect the poison, and if you are not detected they will have no clue. Upon drinking the poison they must make a constitution saving throw. If they succeed they take half damage and aren't poisoned on their next three turns. If they fail they will take 1d12 poison damage immediately and 1d6 damage over three turns of combat. 

At higher levels the damage increases by 1d12 per level casted. The lasting damage over three turns increases by 1d6 as well.