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, diarrhoea, jaundice, gastro-intestinal haemorrhage, 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 and
Clears Toxic Heat and purges knotted Heat and stool from the colon.
Concepts in purgation
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:
- Cold purge (heat clearing): for symptoms such as constipation due to
inflammation and paralysis of the colon - i.e. knotted Heat.
- 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.
- 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.
- Water expulsion: for hydrothorax, ascites, oedema.
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
(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
- 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.
- Purges should not be used during pregnancy as they may cause spontaneous
- 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.
- As purges are mainly used to expel interior excess, if there are also
deficiencies present, tonics should be added.
- As many cases of constipation are simply due to lack of exercise and
improper diet, these factors should always be considered before using purging
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:
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
2) Expel toxic substances from the body
Toxic substances in the colon are expelled by purging. It is also thought
metabolised blood from internal haemorrhaging, bruising and inflammation, may
become "toxic" (as a result of haemoglobin 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 haematoma, contusions, sprains etc.
Purging formulas are especially effective for upper body haemorrhage. As well as
epistaxis, haemoptysis 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 .
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 oedema etc.
These herbs have very severe actions and many are toxic, therefore extreme
caution should be exercised when using them.
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
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 . 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  and Influenza
Significant haemostatic 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 , 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].
Emodin was found to be a strong inhibitor of respiration in Ehrlich ascites
carcinoma cells . This was also observed in leukaemia L1210 cells .
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 leukaemia in mice. Their survival time was
markedly increased and the ascites volume and tumour cell number were decreased
. 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 .
The purgative activity of RH appears to be due to rhein and the sennoside
components . Sennoside content correlated highly with laxative activity,
whereas the correlation between anthraquinone content and laxative activity was
low . Studies on the oxidised products of sennosides suggest that the
sennosides act predominantly on large intestine motility after their degradation
by colonic microorganisms . 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 . Other investigators found that RH increased the
water content of the large intestine, producing a watery stool .
Interestingly, small doses of RH (0.05-0.3g/kg) in some patients can be used to
treat diarrhoea 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%.
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 behaviour and circling movement induced by apomorphine was
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
uraemic syndrome. Clinical trials found that progression to renal failure was
retarded and uraemic symptoms of nausea and anorexia were significantly reduced
[22, 23]. The active principles involved in this effect appear to be the tannin
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 . Oral administration has also been utilised 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 with its effect on joint inflammation