RHUBARB (Da Huang) Rheum palmatum
By Will Maclean and Peter Townsend

Rhubarb (RH) is the dry root and root stock of Rheum palmatum L., Rheum tanguticum Maxim. ex Balf. or Rheum officinale Baill. of the family Polygonaceae. The most commonly used species is R. palmatum. Rhubarb root is one of the oldest and best-known Chinese herbal medicines, first appearing in the Divine Husbandman's Classic of the Materia Medica (Shen Nong Ben Cao Jing) of the latter Han dynasty.
Rhubarb is used as a laxative, antiphlogistic, and haemostatic in the treatment of constipation, diarrhea, jaundice, gastro-intestinal hemorrhage, menstrual disorders, conjunctivitis, traumatic injuries, superficial suppurative sores and ulcers. It is also applied externally for thermal burns. In TCM terms it Drains Heat and accumulations from the Yangming level, Clears Damp Heat, Cools the Blood, Invigorates Blood, eliminates Stagnant Blood, Clears Toxic Heat, and purges knotted Heat and stool from the colon. In order to understand the use of "purges" in TCM it is important to understand the concepts and principles of purgation as applied in herbal practice. The 3 main types of purging are as follows:
1. Cold purge (heat clearing): for symptoms such as constipation due to inflammation and paralysis of the colon - i.e. knotted Heat.
2. Warm purge (inner warming): for acute circulatory disturbance of the digestive tract due to consumption of cold food and drink, and cold environment - i.e. cold accumulation or Yang deficient constipation.
3. Moistening purge (moisten dry intestine): for constipation due to dehydration or poor nutrition resulting in dryness of the intestine (insufficient colonic membrane secretions) - i.e. dry intestine constipation.
4. Water expulsion: for hydrothorax, ascites, and edema.
The following formulas are included in this category:
" Minor Rhubarb Combination (cold purge) (xiao cheng qi tang)
" Major Rhubarb Combination (add Mirabilitum to Minor Rhubarb Combination) (da cheng qi tang)
" Coptis & Rhubarb Combination (cold purge) (san huang xie xin tang)
" Persica & Rhubarb Combination (cold purge) (tao he cheng qi tang)
" Cimicifuga Combination (cold purge - mild) (yi zi tang)
" Apricot Seed & Linum Formula (moistening purge, ma zi ren wan) Wen Pi Tang (warm purge)
Cautions for Using Purges
1. As purging formulas (especially cold purge and water expelling formulas) can cause digestive disorders, they should only be used for as long as it takes to achieve the desired action.
2. Purges should not be used during pregnancy as they may cause spontaneous abortion.
3. If there is a surface condition with mild interior excess, first resolve the surface then purge if necessary. If both surface and interior symptoms are of the same severity, resolve the surface and purge the interior simultaneously.
4. As purges are mainly used to expel interior excess, if there are also deficiencies present, tonics should be added.
5. As many cases of constipation are simply due to lack of exercise and improper diet, these factors should always be considered before using purging formulas.
A Note on Purging
When purging is referred to, most of us will equate it to treatment with laxatives in the normal western sense of the word. However, in TCM purging is not simply used to move stool out of the bowels. Following is a summary of the type of conditions for which purging methods are designed:
1) Anti-inflammatory
The Cheng Qi Tang formulas (Minor Rhubarb Combination [xiao cheng qi tang], Persica & Rhubarb Combination [tao he cheng qi tang]) etc. were not originally designed for treating constipation. Their original application was in febrile diseases where symptoms of high fever, delirium and convulsions occurred. The purging action was used to reduce inflammation. Other formulas, such as Major Bupleurum Combination (da chai hu tang), are useful in treating cholecystitis, gastroenteritis and gastric/duodenal ulcers. Rhubarb has been found to have an inhibitory action on anaerobic bacteria, candida albicans and several other pathogenic microorganisms (see pharmacology). The effect of Rhubarb on anaerobic bacteria is significant in the treatment of cholecystitis and inflammatory conditions of the bile duct, as it has been found that these bacteria are the main aggravating factor in these conditions - especially if accompanied with constipation.
2) Expel toxic substances from the body
Toxic substances in the colon are expelled by purging. It is also thought that metabolized blood from internal hemorrhaging, bruising, and inflammation may become "toxic" (as a result of hemoglobin metabolite overload), and have an adverse effect on the organism, giving rise to "Blood stagnation". In these cases, Blood moving and purging herbs are used together to expel the stagnant blood. The purging method has also been known to be effective for certain types of neuralgia and is widely employed following traumatic injury. Formulas such as Persica & Rhubarb Combination (tao he cheng qi tang) are very useful in the acute stages of hematoma, contusions, sprains etc.
3) Hemostatic
Purging formulas are especially effective for upper body hemorrhage. As well as epistaxis, hemoptysis, and bleeding of the gums, they have also been shown to be effective for cerebrovascular accident. Many contemporary Chinese doctors use RH formulas, particularly Major Rhubarb Combination (da chai hu tang), in order to swiftly eliminate the accumulated Heat and Phlegm via the "big exit". There is clinical evidence from a number of large-scale studies that this method of removing phlegm by enforcing the downward movement of the digestive channels is effective on a large percentage of acute stroke patients [34].
4) Cathartic
Since Rhubarb can also cause constipation if used on its own over a long period of time, it is often used with Mirabilitum. Licorice is also added to prevent cramps and protect the Spleen. In cases of "dry" constipation, such as seen in infants, the elderly and postpartum conditions, herbs which contain oily substances such as Linum (huo ma ren), Dang Gui, Apricot Seed (xing ren), and Persica (tao ren) are used with cathartic agents e.g. Apricot Seed & Linum Formula (ma zi ren wan).
5) Expel Fluids
Certain herbs in this category have a very powerful cathartic effect - that is they cause massive evacuation of fluids and water from body cavities and the intestines in conditions such as hydrothorax, ascites, pulmonary edema, etc. These herbs have very severe actions and many are toxic, therefore extreme caution should be exercised when using them.
Main Constituents
The main constituents of RH are a series of Anthraquinone derivatives: emodin, rhein, aloe-emodin, chrysophanol, physcion, alizarin, citreorosein, etc; Dianthrones: sennoside A~F, sennidin A, palmidin A-C, rheidin A-C etc; Other Glycosides: stilbene, naphthalene, chromones, phenylbutanone etc; Tannins: lindleyin, rhatannin, catechin, epicatechin, gallic acid, cinnamic acid etc.
Antibacterial & Antiviral action
The anthraquinones, aloe emodin, emodin and rhein were found to inhibit in vitro growth of Bacillus subtilis and Staphylococcus aureus, with rhein being the most effective [1]. Antimicrobial activity against Escherichia coli, Micrococcus luteus, Candida albicans, Clostridium perfringens, Fusobacterium varium and Bacteriodes fragilis was also noted [2, 3]. The antibacterial activity appears to be the result of mitochondrial respiratory chain inhibition. Rhein, emodin and aloe emodin specifically interfere with NADH dehydrogenase. The water extract has been found to have an action against Herpes [33] and Influenza virus [34].
Hemostatic effect
Significant hemostatic effect has been demonstrated in Rheum spp, both experimentally and clinically. RH has been found effective in treatment and prevention of experimental gastric bleeding and ulcer formation in rats [4], and in clinical gastro-intestinal bleeding [5, 6, 7]. RH shortened coagulation time, reduced capillary permeability, and improved capillary fragility. It also promoted platelet formation by the bone marrow and induced proliferation of blood capillaries [8, 9].
Antineoplastic effect
Emodin was found to be a strong inhibitor of respiration in Ehrlich ascites carcinoma cells [10]. This was also observed in leukemia L1210 cells [11]. Emodin strongly inhibited the oxidation and dehydrogenation of some amino acids and intermediate metabolites of glucose in Ehrlich ascites carcinoma cells. At 50mg/ml emodin inhibited the oxidation and dehydrogenation of lactic acid in these cells by 87 & 91% respectively. It was further reported that the anthraquinone derivatives rhein, emodin and aloe emodin had an in vivo inhibitory effect against P388 leukemia in mice. Their survival time was markedly increased and the ascites volume and tumor cell number were decreased [12]. In general, it is thought that the antineoplastic activity of RH is mainly due to the inhibition of oxidation and dehydrogenation of the cancer cells [13].
Purgative action
The purgative activity of RH appears to be due to rhein and the sennoside components [14]. Sennoside content correlated highly with laxative activity, whereas the correlation between anthraquinone content and laxative activity was low [15]. Studies on the oxidized products of sennosides suggest that the sennosides act predominantly on large intestine motility after their degradation by colonic microorganisms [16]. The mechanism appears to be hydrolysis of sennosides by microbial b-glycosidase in a stepwise fashion to sennidins A & B, which are then reduced to rheinanthrone, the laxative principle [17, 18]. The active principles of RH seem to act by stimulating Auerbach's plexus or the submucosal nerve plexus [19]. Other investigators found that RH increased the water content of the large intestine, producing a watery stool [20]. Interestingly, small doses of RH (0.05-0.3g/kg) in some patients can be used to treat diarrhea or may increase constipation. At these dosage levels, it is thought that the effect of the tannins in binding stool overcomes the laxative effect. It may also be due to the differences in gut flora and consequent metabolites. Certain species contain more tannins than others, for example R. palmatum contains about 11% tannin, whereas other species range from 4-7%.
Psychotropic action
Rhubarb has a suppressive action on rat ultromotivity. The ultromotive stimulant action of methamphetamine was markedly reduced. Irritability and aggressiveness induced in rats was markedly suppressed by the administration of RH, and, although rather mild, conditioned evasive response was also suppressed. Also, stereotypical behavior and circling movement induced by apomorphine was suppressed [21].
Blood Urea Nitrogen (BUN) reducing action
Recent work in China and Japan has demonstrated that oral or rectal administration of RH is useful in reducing Blood Urea Nitrogen (BUN) in patients with chronic renal failure, and may prevent or delay progression to end stage uremic syndrome. Clinical trials found that progression to renal failure was retarded and uremic symptoms of nausea and anorexia were significantly reduced [22, 23]. The active principles involved in this effect appear to be the tannin fraction [24].
A common method of delivery today is via enema, usually conducted once or twice per week. This method supplements dialysis in areas with inadequate facilities, and enables a reduction in the need for dialysis in some patients. It is thought the surface area of the large intestine enables enough osmotic transfer of BUN from the blood to the intestinal lumen to significantly reduce the load on the kidney [25]. Oral administration has also been utilized successfully, using such formulas as Wen Pi Tang, which includes between 4 and 12 grams of RH.
Anti-inflammatory and Antipyretic action
Lindleyin, one of the tannin fractions of rhubarb, has about the same anti-inflammatory action as aspirin and phenylbutazone and suppresses early stage inflammation [26-28]. It also has a peripheral analgesic action which is comparable with aspirin and phenylbutazone; its effect on joint inflammation is similar to aspirin [29]. Also, the bound tannins have a free radical scavenging action [30]. Rabbits with fever induced by subcutaneous inoculation of pneumococci responded with decreased body temperature after oral administration of RH [31].
Sample clinical studies
Seventy-six women with endometriosis of the "Blood Stasis with lower abdominal masses" type were treated in Long Hua Hospital, Shanghai, with a prescription featuring rhubarb as the chief ingredient. Total effectiveness rate was 80.26%, with reduction in dysmenorrhea in 88.89%, pelvic pain 66.72%, dysparenuria 72.12%, reduction in mass size 22.15%; three cases of twenty-two infertile women fell pregnant (13.63%). The results support the idea that rhubarb can eliminate Blood Stasis and invigorate the circulation of Blood. Other common rhubarb based combinations used for the treatment of endometriosis include Persica and Rhubarb Combination (tao he cheng qi tang) and Nei Yi Wan, composed of rhubarb, amber (hu po) and tortoise shell (bie jia).
Hypertension during pregnancy
Shanghai Medical University conducted a double blind study with processed rhubarb (low dose of 0.75g/day) in pregnant women at risk of pregnancy-induced hypertension (PIH). Rhubarb (140 cases) and placebo (125 cases) was given to women at risk of PIH consecutively from the 28th week of gestation to delivery, with another 68 pregnant women as control. In the treated group, 5.7% of the women developed PIH, whereas in the untreated group 20.8% developed PIH. This result was statistically significant (P<0.01). The mechanism of this apparent protection may be related to the inhibition of Plasminogen activator inhibitor (PAI), plasma Fibronectin (Fn), and decreased damage to the vascular endothelium [38]. Interestingly, the tannin components of RH have also been found to have ACE-inhibiting actions [39].
Acute inflammatory diseases
RH has Heat clearing, antipyretic and purgative action and as such is much employed in compound prescriptions like Persica & Rhubarb Combination (tao he cheng qi tang), Major Rhubarb Combination (da cheng qi tang), Coptis and Rhubarb Combination (san huang xie xin tang), Major Bupleurum Combination (da chai hu tang) etc. for acute inflammatory diseases characterized by fever, constipation, abdominal distension, thirst and general malaise. Rhubarb prescriptions have been found effective in such biomedically defined disorders as acute appendicitis, acute pancreatitis, acute cholecystitis, and other acute abdominal infections [35, 36].
Pharmacokinetics and Toxicity
RH is readily absorbed after ingestion. The serum drug concentration peaks after two hours, and when used for purgation, the bowels generally move after 6 - 8 hours. Habituation may be a problem in some patients with long-term use for constipation, and thus RH generally should be phased out and other appropriate therapeutic measures instituted or other herbs that address the "root" of the problem added to the formula.
Generally, RH is low in toxicity, but intoxication could result from overdosage, especially of the fresh herb. Toxic symptoms include nausea, vomiting, dizziness, abdominal colic and jaundice. Long-term use of the anthraquinone cathartics could lead to liver cirrhosis and hypokalemia [32].
Use in Combination
Rhubarb and Mirabilitum (mang xiao)
The Bitter & Cold characteristics of Rhubarb aid in the dispersal of Heat and the removal of stagnant Damp-heat. Mirabilitum (mang xiao) is salty and cold; it moistens dryness and softens hardness. These two substances work synergistically to resolve stagnation and accumulation of the intestines and stomach as well as disperse Heat. They are most commonly used together in the treatment of Heat accumulation type constipation, resulting from knotted dryness of the stomach and intestines, or febrile diseases due to a knotted pathogen resulting in Yang Ming type Fever, abdominal distension and pain, and constipation with dry stool. This combination used with Licorice (gan cao) results in the formula Regulate Stomach Cheng Qi Tang (tiao wei cheng qi tang). Licorice, which is Sweet and Warm, counteracts the overly Cold and strong acting actions of Rhubarb and Mirabilitum and protects the Stomach Qi from damage.
Rhubarb and Coptis (huang lian)
A combination of these two herbs is known as da huang huang lian xie xin tang. Both herbs are Bitter & Cold and clear Heat. Rhubarb is superior in its descending action while Coptis has a superior Heat clearing, Damp drying action. When the two are combined, they are very effective in the treatment of pain and distension due to knotted Heat pathogen. If these two herbs are also combined with Scute, which cools Hot Blood and stops bleeding, it creates the formula Coptis and Rhubarb Combination (san huang xie xin tang). This formula is very effective for treating epistaxis and hemoptysis due to a Heat pathogen in the Blood causing frenetic Blood syndrome. The combination of these three herbs is not only used for clearing excess Heat from the Qi level (Qi Fen) but also used to purge Heat toxin from the Blood level and resolve the various symptoms that occur due to this.
Rhubarb and Capillaris (yin chen)
This combination of herbs is effective for the clearing and dispersal of Damp-heat and it is very commonly used to treat jaundice. The combination of these two herbs with Gardenia (zhi zi) is known as Capillaris Combination (yin chen hao tang). This formula drains Heat from the Gall Bladder, with Gardenia aiding the expulsion of Damp-heat through the urine. This is a standard combination used to treat jaundice due to excess type Damp-heat.
Rhubarb and Cinnamon Bark (rou gui)
Rhubarb is very Cold and disperses and descends. Cinnamon bark is used as an adjunct herb to prevent damage to Spleen Yang. This method of treatment is known as the Synergy of Hot and Cold and is a common treatment for habitual constipation.
Rhubarb and Gypsum (calcined, duan shi gao)
The combination of these two herbs powdered and made into a paste can be useful in the treatment of burns and other excess heat skin conditions. Another external use of Rhubarb is in a 10:2 mixture with powdered licorice for the treatment of chronic leg ulcers.
Other common combinations include Rhubarb and Moutan (mu dan pi) for the treatment of Blood stagnation, Rhubarb and Zhi Shi for the treatment of excess stomach accumulation, Rhubarb and Apricot Seed (xing ren) for the treatment of dry deficient type constipation, and Rhubarb and Persica (tao ren) for the treatment of dry type constipation and/or Blood stagnation.
When used to regulate the Blood and break up Stagnant Blood, small quantities of RH are needed; when purging, use larger amounts (up to 15 grams in Yangming syndrome). Unprocessed RH is a stronger purge than processed; RH fried in wine (jiu da huang) can clear Heat from the upper body; charred RH (da huang tan) is used to stop bleeding. When used as a purge, RH should be added about 5 minutes before the end of cooking time (hou xia); to regulate Blood and clear Stagnant Blood it may be cooked longer. RH (especially the raw, unprocessed product) is generally contraindicated during pregnancy, during menstruation and breast-feeding, post-partum, in exterior syndromes, and for Spleen and Stomach Xu Cold conditions. Use caution in cases involving Qi, Blood and Yang Xu.
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