Meng Shi

Structural rather than pharmacological. Biotite is a layered aluminosilicate that is essentially insoluble at neutral pH and only partly attacked by gastric acid, so the drug's classical heavy, descending action is a physical and mineral-loading effect rather than the action of an absorbed molecule. Its iron and magnesium are the fraction that can enter solution.

The carbonate fraction is the pharmacologically live part of this grade: it neutralises gastric acid and evolves carbon dioxide on contact with it, which is a real antacid effect that the biotite grade does not share. Two rock types with different acid behaviour are dispensed under one drug name, so which one reached the dispensary changes what the patient receives.

Inert ballast. It contributes nothing pharmacologically but is part of why the drug is dosed by weight in grams while contributing far less soluble material than that weight suggests.

Named here because Meng Shi is not one mineral. Chinese practice recognises a green grade and a gold grade with different mineralogy, and they are not interchangeable analytically even though prescriptions are often written for Meng Shi without qualification. Vermiculite expands dramatically on heating, which is why the gold grade behaves differently under the traditional calcination.

This is the constituent that makes Meng Shi a preparation-dependent safety question rather than an inert stone. The classical method seals the mineral with an equal weight of saltpetre in a luted crucible and fires it to redness until gold flecks appear; the nitrate is meant to be consumed in the firing. An incompletely fired batch carries residual nitrate into the patient, and nitrate is not a trivial contaminant in infants, in whom it is reduced to nitrite and can cause methaemoglobinaemia. No published assay of residual nitrate in commercial calcined Meng Shi was located for this record.

Recorded as an open question rather than a finding. Tremolite occurring in asbestiform habit is a known human carcinogen and is the contaminant that caused mesothelioma and excess mortality in vermiculite miners; Jin Meng Shi is a vermiculite schist. Whether medicinal Meng Shi carries asbestiform amphibole is simply unknown - no assay was found either way, and absence of an assay is not evidence of absence. It is a reason to prefer a supplier who provides mineralogical characterisation and to avoid grinding the raw stone in an unventilated dispensary.

The plausible route by which a mineral drug interacts with co-administered medicines: polyvalent cations chelate several common drug classes in the gut lumen. The quantities have not been measured for this drug, so the interaction is mechanistic rather than documented.

The first materia medica to record Meng Shi, which is late for a mineral drug and marks it as a Song-era addition rather than part of the Han canon. The alternative names it preserves, susu shi and lan shi, describe a friable stone that crumbles readily - the physical property that makes the drug grindable at all.

Gives the calcination recipe in reproducible detail: two liang of crushed Meng Shi with two liang of saltpetre in a small sand crucible, covered with a tile, bound with iron wire, luted with salt mud, sun-dried, then fired until red with gold stars showing, cooled and ground extremely fine. This is the text that makes the saltpetre step explicit, and therefore the text that makes the processing a safety variable.

Source of Gun Tan Wan, the formula that fixed Meng Shi's clinical identity as the drug for stubborn congealed phlegm. Its composition - Meng Shi and saltpetre two liang each, calcined and water-refined down to one liang, with eight liang each of wine-steamed Da Huang and wine-washed Huang Qin and five qian of Chen Xiang - shows that the mineral was always a small part of a large purgative, which is how its dose should still be read.

Records the drug's descending, downward-driving nature and confines it to excess phlegm patterns in robust patients, warning against use in the depleted and in pregnancy. The classical restriction and the modern caution about a drastic purgative formula are the same caution.