Black Lead Classic Formulas — Natural Herb Library

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Suppresses counterflow and strongly descends rebellious Qi - classically used for severe wheezing, dyspnea, and upper excess/lower deficiency patterns in which the Kidneys fail to grasp Qi and the breath rises upward.
Anchors floating Yang - used when depleted Kidney Yang cannot hold Yang at the root, producing agitation above with cold weakness below, often alongside palpitations, anxiety, or false-heat manifestations.
Transforms phlegm and opens obstructed upper pathways in formulas that address phlegm clouding with sudden collapse, epilepsy, or severe chest and throat obstruction.
Serves as a drastic emergency mineral within rescue-style formulas - its heavy descending action is never used casually and is traditionally balanced with strong warming Yang restoratives.

Hei Xi Dan (黑锡丹) - from Tai Ping Hui Min He Ji Ju Fang, the defining formula for Hei Xi, pairing lead with sulfur and warming Kidney-Yang herbs to anchor floating Yang and descend wheezing from upper excess and lower deficiency.

Modern TCM materia medica summaries such as Me & Qi describe Hei Xi as sweet and cold, entering the Liver and Kidney channels to descend counterflow Qi, anchor floating Yang, transform phlegm, and assist severe Kidney failure to grasp Qi.
Ben Cao Gang Mu notes a historical confusion between lead and tin in earlier materia medica transmission; that identity problem appears to be reflected in this import record's original English and Latin labels.
Classical cautionary sources including Ben Cao Jing Shu and Ben Jing Feng Yuan warn that Hei Xi is unsuitable in weak digestion, pure Yang collapse without floating counterflow, or when processing is inadequate.