Xiao Yao San vs. Dang Gui Shao Yao San

The two formulas share four of their herbs, and both are mainstays of gynecology. What separates them is the engine of the pattern — constrained qi in one, thin blood with accumulating dampness in the other.

The one-line difference

Xiao Yao San is chaired by chái hú and organized around moving constrained qi. Dang Gui Shao Yao San (当归芍药散, from Zhang Zhongjing's Jin Gui Yao Lue) has no chai hu at all: it doubles down on blood — dang gui, a large dose of white peony, chuan xiong — and on water, with poria, atractylodes, and ze xie draining the dampness that gathers when blood and fluids fall out of step^[1].

When each fits

Dang Gui Shao Yao San's picture centers on the abdomen: continuous dull cramping pain (classically in pregnancy and menstruation), puffiness and edema, heaviness, dizziness — blood deficiency with dampness, without the emotional signature.

Xiao Yao San's picture leads with the emotional and stress-linked signs — irritability, mood swings, distension that worsens under pressure — with the deficiency in a supporting role.

Shared DNA, different chairs

Four herbs — dāng guī, bái sháo, bái zhú, fú líng — sit in both prescriptions, a reminder that classical formulas are families built from recurring modules. The module is the same; the chair changes the meaning: add chai hu and mint and the formula faces outward toward constraint, add chuan xiong and ze xie and it faces inward toward blood and water^[1].

Differential logic, not a recommendation — especially here, where the classical indications include pregnancy: strictly practitioner territory.