Potion of Poison

This potion comes in many guises, and always appears to be a beneficial potion (most often the swirling red of a potion of healing ). Its true intent, however, is deadly. 

When you drink this potion you take 3d6 poison damage and make a DC 13 Constitution saving throw or become poisoned . At the beginning of each of your turns while poisoned in this way, you take 3d6 poison damage. At the end of each of your turns you repeat the saving throw, decreasing the damage dealt by the poison by 1d6 for each successful save. You cease to be poisoned when the damage is reduced to 0.