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Shennong Bencao Jing
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Dahuang (Rhubarb Root) — classical plate
Rhei Radix · Rhubarb Root Plate 014
Rhei Radix
大黄 Dahuang
Rhubarb Root
Radix et Rhizoma Rhei
Nature & FlavorBitter; cold
ChannelsSpleen, Stomach, Large Intestine, Liver, Heart
Actions
Drains heatUnblocks the bowelsSweeps out stagnationMoves blood
Six ChannelsThe chief herb of Yangming disease
The ClassicThe original text

「味苦寒。主下瘀血，血闭，寒热，破癥瘕积聚，留饮宿食，荡涤肠胃，推陈致新，通利水谷，调中化食，安和五脏。」

Bitter in flavor, cold. It drives out static blood and blocked menses, cold and heat, breaks up masses and accumulations, retained fluids and lodged food, sweeps the stomach and intestines clean, pushes out the stale and brings in the new, frees the passage of water and grain, regulates the center and transforms food, and brings peace to the five organs.

RootBro's note — 'Push out the stale, bring in the new' is the essence of dahuang in four characters — it is not a simple laxative but a complete program for clearing metabolic waste and restoring gut function. The three Chengqi decoctions are built on dahuang sweeping out Yangming heat-bind.
PhD InsightA systems-biology reading
Its key constituents are the anthraquinones — emodin, rhein and relatives. They stimulate the intestinal mucosa to drive peristalsis while inhibiting water absorption in the gut, producing a powerful draining action.
Emodin · 大黄素
Inhibits Na⁺-K⁺-ATPase → water secretion into the intestinal lumen ↑ → stool softens. Activates the myenteric nerve plexus → peristalsis ↑ → the stale is pushed out. At small doses it is also antibacterial and anti-inflammatory.
A modern reading of 'sweeping out stagnation': Yangming abdominal excess is, at bottom, gut-microbiome disorder + impaired intestinal motility + accumulated inflammatory mediators. Dahuang's anthraquinones clear the intestinal contents in one pass and break the vicious cycle — the most direct 'reboot' strategy in the classical formulary.
Logic PairingClassical pairings
Da Chengqi Tang (Major Order-the-Qi Decoction)Xiao Chengqi Tang (Minor Order-the-Qi Decoction)Tiaowei Chengqi Tang (Regulate-the-Stomach Order-the-Qi Decoction)Dahuang Huanglian Xiexin Tang (Rhubarb & Coptis Decoction to Drain the Epigastrium)Taohe Chengqi Tang (Peach Pit Order-the-Qi Decoction)Dahuang Fuzi Tang (Rhubarb & Aconite Decoction)
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