Numbing Dose is a common Enchantment — Aura card from New Phyrexia (NPH), collector number 40. Current market price: $0.07 (foil $0.17), TCGplayer market prices via Scryfall.
Enchant artifact or creature Enchanted permanent doesn't untap during its controller's untap step. At the beginning of the upkeep of enchanted permanent's controller, that player loses 1 life.