Han Shui Shi

Stated first because nothing below can be read without it. Han Shui Shi is a name, not a substance. Modern commercial material divides on a north–south line: northern practice dispenses red gypsum (北寒水石, Gypsum Rubrum, hydrated calcium sulfate), southern and Tibetan practice dispenses calcite (南寒水石, Calcitum, calcium carbonate). Textual research holds that the drug the classical texts meant was neither — that the Ning Shui Shi of the Shen Nong Ben Cao Jing was the natural crystal of mirabilite, a hydrated sodium sulfate, and that Tang and Song physicians who no longer recognised the original substituted gypsum and calcite, an error transmitted for close to a thousand years. This record names calcite or gypsum and does not choose between them; that ambiguity is itself the principal safety finding, because the three candidates behave differently in the gut.

Calcite is insoluble in water but dissolves readily in gastric acid, releasing calcium ion and carbon dioxide and consuming hydrogen ion. In pharmacological terms this material is an antacid and a calcium supplement, and it is the arm of the identity problem that carries the real drug interactions: absorbed calcium chelates tetracyclines, fluoroquinolones and bisphosphonates in the gut, blocks levothyroxine absorption, and at sustained high intake with alkali produces the calcium-alkali (milk-alkali) syndrome. Raising gastric pH also alters the absorption of pH-dependent drugs independently of the calcium.

Gypsum is sparingly but genuinely soluble in water (of the order of 2 g/L), so unlike calcite it releases some calcium into a decoction without needing gastric acid, and unlike calcite it does not neutralise stomach acid or generate carbon dioxide. The calcium-mediated chelation interactions apply here too but on a smaller molar basis per gram, and the antacid and milk-alkali risks essentially do not. This drug is also close kin to Shi Gao, a current Pharmacopoeial material, which is a further route by which the two get interchanged.

Pharmacologically this is a different class of drug: freely water-soluble, poorly absorbed, and therefore an osmotic saline purgative, which is exactly how the Pharmacopoeia describes mirabilite (Mang Xiao) — for abdominal distension, abdominal pain and constipation. It is also a sodium load. The alias set preserved for Ning Shui Shi points the same way: Yan Jing (salt essence), Yan Jing Shi, Yan Zhen and Yan Gen are all salt-lake names. A patient given mirabilite in the belief they are taking an inert calcium mineral gets purgation, fluid and electrolyte loss, and sodium, none of which the prescriber intended.

The practical reading is that origin materially changes the elemental composition of Nan Han Shui Shi, enough that multi-element and isotope data can be used to authenticate provenance. That is a quality-control result rather than a toxicological one: the study characterised regional differences, it did not report toxic element burdens against any limit.

This is the worst regulatory position of the five minerals in this batch. There is no national monograph, therefore no national identity definition, no national assay and no national arsenic, lead, cadmium or mercury limit; and the provincial standards that do exist encode the north–south split rather than resolving it. A supplier can ship either mineral, in compliance with some standard somewhere, under the same name. Compare Gypsum Fibrosum and Mirabilitum, both of which do have Pharmacopoeial monographs — the safer course is to prescribe the named Pharmacopoeial drug that matches the intended action rather than this name.

Source of first record, under the name Ning Shui Shi rather than Han Shui Shi. The alias set transmitted with it — Yan Jing (salt essence), Yan Jing Shi, Yan Zhen, Yan Gen, Bing Shi — is a salt-lake vocabulary, and it is the main textual reason modern scholarship identifies the original drug as natural mirabilite crystal rather than as any calcium mineral.

Transmits Han Shui Shi as a synonym of Ning Shui Shi, which is how the later name entered general use. The name change is the point at which the drug's identity begins to drift away from the substance the Ben Jing described.

Han Shui Shi appears at six liang alongside talc, red and white halloysite, shi ying and gypsum, with dragon bone, oyster shell, rhubarb, dried ginger, cinnamon twig and licorice, for heat-type paralysis and epilepsy. This is the drug's principal classical formula, shared with Zi Shi Ying. Because the formula also contains gypsum in its own right, an edition of Feng Yin Tang made with northern red gypsum as Han Shui Shi is a formula containing gypsum twice under two names.

The consensus reconstruction is that Tang and Song physicians no longer recognised the original mineral and substituted gypsum and calcite for it, and that the substitution has been transmitted for close to a thousand years. Northern practice settled on red gypsum, southern and Tibetan practice on calcite. This is why the name cannot be resolved from the classical literature alone: the texts after the Tang are describing whichever substitute their authors had.

Han Shui Shi has no monograph in the national Pharmacopoeia and exists only in these provincial standards, which encode rather than resolve the north–south divergence in base mineral. Gypsum Fibrosum and Mirabilitum, by contrast, are both national Pharmacopoeial drugs with defined identity and assay.