Xiang Su San (Cyperus and Perilla Powder) xiāng sū sǎn · 香苏散

Safety. Xiang Su San is recorded in Taiping Huimin Hejiju Fang. Four herbs: stir-fried xiang fu, zi su ye, chen pi and honey-fried gan cao. It is the mildest formula in this batch, and its mildness is precisely why it is worth writing about carefully rather than briefly. Read it against Ma Huang Fu Zi Xi Xin Tang, the other end of the same shelf. That formula is three herbs and all three are among the most regulated botanicals in the English-speaking world. This one is four herbs and none of them is on that list. Both are called exterior-releasing. The difference is not a matter of degree only: the classical distinction here is that the presenting problem is as much stagnant qi as an exterior attack — a tight, oppressed feeling in the chest and epigastrium, poor appetite, and a chill that will not settle. Xiang fu is the herb traditionally described as moving qi and is the reason the formula carries its name; zi su ye releases the exterior and moves the middle; chen pi rectifies qi and dries damp; gan cao harmonises. A powder rather than a decoction, it sits in the part of the tradition that expects a person to be up and about. The reason to be careful rather than brief is that mildness is exactly what invites self-treatment. A person who would never take a formula containing aconite will happily take four kitchen-adjacent herbs, and the reasoning is understandable — but the reasoning does not exclude anything. The chill that will not settle may be influenza, COVID-19, pneumonia, a urinary infection in an older person, or the early phase of something that declares itself in the next two days. Chest tightness has its own short list, and chest tightness with breathlessness, sweating, nausea or radiation to the arm, jaw or back belongs on an emergency pathway regardless of what a person took for it. Persistent cough beyond eight weeks has a differential that includes tuberculosis, bronchiectasis and lung cancer, and none of it is settled by a powder. On safety: chen pi is citrus peel, and the similarly named hua ju hong is pomelo peel, a different substance. Gan cao carries the risk of apparent mineralocorticoid excess with daily intake, which is why this library notes it even in a four-herb powder. This library does not claim the formula releases the exterior, moves qi, or treats colds, indigestion or any specific disease.