The antonyms for the word "juices up" include dull, diminish, dampen, quell, weaken, and deaden. When something is "juiced up," it means that it's been energized, boosted, or invigorated. On the other hand, if something is dull, it lacks luster, brightness, or vitality. If something is diminished, it means that it has been reduced, subdued, or lessened in some way. To dampen something is to make it less intense or enthusiastic, while to quell something is to pacify or suppress it. To weaken something is to make it less strong or potent, and to deaden something is to dull its sensitivity or responsiveness.