Chief in Xiao Yao San

Chái Hú 柴胡

Bupleurum root · Bupleuri Radix (Bupleurum chinense) · 30 g in the classical formula

Role in the formula

Chái hú is the chief herb — the reason Xiao Yao San exists. Its defining action in the tradition is to course the liver and relieve constraint: to restore movement where qi has become stuck, which classical medicine locates in the liver's charge over the smooth flow of qi and emotion^[1]. Everything else in the formula either supports this movement or protects the body while it happens.

Character

Bitter and acrid, slightly cool, entering the liver and gallbladder channels^[1]. Beyond soothing constraint, chái hú is traditionally said to raise clear yang and to resolve lingering half-exterior conditions — it chairs some of the most famous prescriptions in the literature, including the Bupleurum family of formulas from the Shang Han Lun.

In the pharmacy

The root of Bupleurum chinense (or B. scorzonerifolium), typically sold dried and sliced. In Xiao Yao San it appears at 30 g in the classical powder proportions — equal to the deputies, a deliberately gentle architecture.