Background
In TCM, yīn xū describes a state where the body's cooling, moistening, and anchoring substance is insufficient. Without enough yin to temper yang, a kind of "empty heat" arises — not the fever of an infection, but a low-grade internal warmth that flares at night, dries the mouth and throat, and makes restlessness feel like the new normal. The formulas under this tag form the most recognizable family on the entire site: they are all variations on the Rehmannia Six-Flavor root (Liù Wèi Dì Huáng Wán). Zhibai adds ingredients to clear that "empty heat"; Maiwei targets the lung-and-kidney axis specifically. What connects them is the same underlying logic — replenish the coolant so the radiator stops running hot — but each does it with a different emphasis, which is why a reader encountering two of them on the same concern page might wonder "what's the difference?" This tag exists to answer that.