Prepared Rhubarb Root Classic Formulas … Natural Herb Library

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Moderates the harsh purgative force of raw Da Huang ... prepared rhubarb is used when the formula still needs bowel-unblocking, heat-clearing, or blood-moving action but in a less abrupt or less cold form.
Invigorates blood and disperses stasis ... it is used for fixed abdominal pain, traumatic injury, and menstrual pain when blood stasis and heat or accumulation are part of the pattern.
Clears damp-heat and constrained accumulation ... traditional use extends to jaundice, focal distension, and internal heat obstruction where raw Da Huang would be too drastic.

Tao He Cheng Qi Tang modification logic ... when blood stasis and accumulation coexist but excessive purgation is not desired.
Da Cheng Qi Tang lineage adaptation ... prepared Da Huang may be selected when opening the bowels is still needed but the raw herb would be too forceful.
Trauma and gynecologic formulas ... processed rhubarb is used when blood stasis and heat need dispersing without overdriving the intestines.

Rhubarb processing traditions are among the classic examples of paozhi changing the balance between purgation, heat clearing, and blood-moving use.
Materia medica teaching usually treats prepared Da Huang as milder on the bowels and somewhat more suitable for blood-stasis and recovery settings than the raw product.