Rhubarb Root (Rhei Radix): A Comprehensive Reference
1. Identity, Botanical Classification, and Natural Source
Botanical names and taxonomy. Rhubarb is a collective name for various perennial plants of the genus Rheum L. from the Polygonaceae family. Currently, the types used in traditional Chinese medicine have stabilized to three species: Rheum palmatum L., Rheum tanguticum Maxim. ex Balf., and Rheum officinale Baill. A fourth species, Rheum rhaponticum (Siberian rhubarb), yields the registered special extract ERr 731®, which is used to alleviate menopause-related complaints.
Plant description and geography. Rheum palmatum is a perennial herbaceous plant growing to 1.5–2 m tall, with large, jagged, hand-shaped leaves growing 40–60 cm wide and long. The tiny pink flowers appear in panicles up to 1.5 m tall, and the plant produces thick, deep roots. R. palmatum is mainly produced in Gansu and Qinghai, China, and is mostly cultivated, accounting for the majority of rhubarb production in China. R. tanguticum is also mainly produced in Qinghai and Gansu, wild or cultivated. R. officinale is mainly produced in Sichuan and Guizhou, cultivated or wild, with relatively low yield.
Common names. Some common names associated with Rheum palmatum—"Russian rhubarb," "Turkey rhubarb," and "Indian rhubarb"—are directly affiliated with the trade routes for rhubarb from China. The Chinese name for the root and rhizome is Da Huang.
Medicinal part and standardized preparations. Medicinal rhubarb consists of the dried rhizome and root of R. officinale Baillon or R. palmatum, of related species/hybrids grown in China (Chinese rhubarb), or of Rheum emodi or Rheum webbianum native to India, Pakistan, or Nepal (Indian rhubarb). The European Medicines Agency's Herbal Medicines Committee (HMPC) conclusions cover rhubarb root preparations obtained by drying and comminuting (reducing into tiny pieces) the root; the dried, comminuted root may also be extracted with a solvent. Rhubarb root preparations are standardized to contain a defined amount of anthraquinones, which are the substances linked with the activity of the preparations. Herbal medicines containing rhubarb root are usually available as herbal tea and in liquid and solid forms to be taken by mouth. Rhubarb root preparations may also be found in combination with other herbal substances in some herbal medicines.
TCM processing forms. Common concoctions in traditional Chinese medicine include raw rhubarb, wine rhubarb, cooked rhubarb, and rhubarb charcoal. The laxative efficacy of raw rhubarb tends to diminish when processed, likely due to the decomposition and inactivation of anthraquinones during processing.
2. Traditional and Historical Use
2.1 China
Rhubarb has important economic value, used as a purgative drug in China since the third millennium BC, and was first recorded in Shen Nong's Herbal Classic. Rheum palmatum (or dahuang) is an important crop that has been used in traditional Chinese medicine for over 2,000 years. Rhubarb has been suggested to exert eliminating heat, purging fire, cooling blood, dispersing blood stasis, dredging collateral antidotal and purgative effects, and was used to treat constipation, diabetic nephropathy, chronic renal failure, acute pancreatitis, and gastrointestinal bleeding.
Historical records of rhubarb processing date back to the Han Dynasty, with continual innovations. The preparation of Rheum palmatum in traditional Asian practices typically involves harvesting the roots and rhizomes in autumn from plants at least three years old, followed by cleaning, slicing, and sun-drying to preserve potency. These dried materials are then commonly decocted in water to create herbal teas or added to multi-ingredient formulas, with processing methods like stir-frying or steaming sometimes applied to modulate its effects, such as reducing its strong purgative action for gentler use.
2.2 Trade and Spread to Other Cultures
The dried roots of Chinese rhubarb became one of the most prominent items traded along the Silk Road, and imported roots of various rhubarb species were widely used in Europe for hundreds of years before the identity of the plant was eventually discovered.
Rheum palmatum spread from continental China to Europe via Russia, and was introduced to Japan as a laxative when Dutch medicine was introduced in the late Edo period. Since the Meiji era (1868–1912) in Japan, the use of rhubarb was re-evaluated, and rhubarb was registered in the Japanese Pharmacopoeia.
Beyond China, Rheum palmatum features prominently in Tibetan medicine, where it is employed to treat hepatitis, cholecystitis, and blood disorders, often combined with other herbs to balance its cooling effects.
2.3 Traditional Persian and Other Traditions
In Traditional Persian Medicine (TPM), rhubarb is used for edema, amenorrhea, abdominal pain, tenesmus, and delirium. In various traditional systems, it has been used as a laxative, tonic, diuretic, and to treat fever, cough, indigestion, and menstrual disorders since antiquity.
2.4 European Use
Since the beginning of the 1990s, ERr 731®, an extract isolated from the roots of Siberian rhubarb (Rheum rhaponticum), has been used in Europe for the treatment of women suffering from oligomenorrhoea or amenorrhoea (trade names Phyto-Strol® and femi-loges®). In addition to its indication for constipation according to the German Commission E, there are clinical evidences supporting its therapeutic effects in respiratory diseases, intestinal obstruction, and chronic renal diseases.
3. Key Constituents and Active Compounds
About 200 compounds have been isolated from rhubarb, including anthraquinones, anthrones, stilbenes, flavonoids, acylglucosides, and pyrones. The following classes represent the most pharmacologically significant:
3.1 Anthraquinones
Rhubarb (Rheum officinale, Rheum palmatum) root contains anthraquinones (e.g., aloe-emodin, chrysophanol, emodin, rhein), which are cathartics, and tannins, which are astringents. The major bioactive components of R. palmatum responsible for antimicrobial activities are five hydroxyanthraquinones (HAQs): aloe-emodin, rhein, emodin, chrysophanol, and physcion. The root and rhizome also contains sennoside B, sennoside A, aloe-emodin, rhein, emodin, and chrysophanol.
3.2 Stilbenes and Other Phenolics
Stilbene glycosides, including rhaponticin and the metabolite rhapontigenin, have been identified in the root. Tannins, sennosides, catechins, gallic acid, and cinnamic acid have been identified. Lindleyin, a phytochemical with estrogenic activity, has also been described. Rhubarb is also a dietary source of resveratrol.
3.3 Mechanisms of Action: Laxative Effects
According to published pharmacokinetic analysis, anthrone-glycosides are carried unabsorbed to the large intestine, where the active aglycone is released by bacterial hydrolysis of the sugar. The intestinal bacterial flora also reduces anthraquinone aglycones to the corresponding anthrones. After absorption, the anthranoids are transformed mainly to their corresponding glucuronide and sulfate derivatives, which appear in urine and bile.
In addition to the sennosides present in rhubarb extracts, which have been traditionally used as a laxative, emodin and other anthraquinones exert action on the GI tract. Emodin is metabolized in the large intestine by intestinal bacteria and converted to aglycone, which exerts various effects on absorption, secretion, and motility in the tract, and is also suggested to increase peristalsis without affecting the stomach or duodenum.
When used in small doses, the tannin content in rhubarb has a constipating effect. At higher doses, however, the hydrolyzed metabolites of emodin and sennidin stimulate the gastrointestinal tract and produce a laxative effect. The actions of anthraquinones on rheinanthrone, which is transformed from sennoside A, may promote the purgative effects of sennoside A.
3.4 Mechanisms of Action: Anti-inflammatory and Renoprotective Effects
Network pharmacology analysis suggests that rhubarb's therapeutic action in chronic kidney disease primarily involves modulation of the NF-κB signaling pathway, with IL-6, IL-1β, TNF, PTGS2, and NFKBIA identified as key targets. R. palmatum plays roles as an anticoagulation and antithrombosis agent and improves microcirculation through lowering the endotoxin-induced permeability of microvascular tissue, reducing tissue edema, decreasing inflammatory exudation and necrosis, and enhancing cytoprotection mechanisms.
3.5 Mechanisms of Action: Estrogenic Activity (Rhapontic Rhubarb)
ERr 731 — a standardized botanical extract of Siberian rhubarb (Rheum rhaponticum L.) high in rhaponticin — acts like a selective estrogen receptor modulator for ERβ receptors and may offer a higher degree of safety while maintaining the desired efficacy profile. The ERr 731 extract, as well as its individual compounds, have been demonstrated to act as potent, selective ERβ agonists in human endometrial cells, without significant ERα effects.
3.6 Mechanisms of Action: Antitumor Activity
To determine the possible molecular mechanisms of the anti-cancer effect of rhubarb, researchers have focused on the free anthraquinones, with emodin being the most frequently studied. Emodin has been found to inhibit the proliferation of tumor cells and induce apoptosis; one study found emodin inhibited the growth of the human pancreatic cancer cell line Panc-1 in a concentration- and time-dependent manner. Additionally, it could inhibit the growth of tumor blood vessels; one investigation of 95% ethanol extract fractions on a zebrafish model found that anthraquinones with acidic or polar, hydrophilic substitution at C-6 or C-3 positions played a substantial role in inhibiting angiogenesis. These findings are preclinical only.
4. Scientific Evidence by Area of Use
4.1 Constipation (Laxative Use)
Regulatory conclusions. The HMPC concluded that rhubarb root preparations can be used for the short-term treatment of occasional constipation; rhubarb root medicines should only be used in patients over the age of 12 years and should not be taken for more than a week. The German monograph of Rhei radix indicates a daily dose of 20–30 mg of hydroxyanthracene derivatives calculated as rhein, but recommends that the pharmaceutical form must allow lower dosages than the usual daily dose.
Clinical evidence. A study in middle-aged adults showed that a rhubarb extract at 12.5 mg or 25 mg, taken at bedtime for one month, improved stool frequency and consistency compared with placebo. Studies comparing the laxative effects of four rhubarb concoctions (raw rhubarb, wine rhubarb, cooked rhubarb, and rhubarb charcoal) on healthy mice found that only raw rhubarb and wine rhubarb exhibited significant laxative effects, occurring approximately 3 hours post-administration. Rhubarb acts within 8 to 12 hours due to the time taken for transport to the colon.
Evidence strength. The short-term laxative indication is well-established by European regulatory review, supported by the HMPC, Commission E, ESCOP, and WHO. Human clinical data on rhubarb as a standalone laxative are, however, largely older or conducted alongside other herbs.
4.2 Chronic Kidney Disease and Renal Failure
Clinical evidence. In a prospective clinical trial conducted in 151 patients with chronic renal failure, the progression rate of renal failure was slowed in patients treated with rhubarb, with an increase in both the plasma albumin and transferrin level, pointing toward an improved nutritional status.
A prospective comparative study was conducted in patients with chronic kidney disease (stages 3 and 4) attending a renal clinic. Patients were randomly divided into two interventional groups; the control group received conservative management while the rhubarb group received conservative management along with a rhubarb capsule (350 mg, three times daily) for 12 weeks. Haemogram and renal function tests were measured at 0, 4, 8, and 12 weeks of treatment. There was progressive improvement in clinical features in both groups after 12 weeks of treatment, but the rhubarb group showed more marked improvement compared to the control group.
Meta-analytic evidence. A systematic review and meta-analysis found that rhubarb alone or traditional Chinese medicine compounds containing rhubarb can significantly reduce serum creatinine, blood urea nitrogen, and uric acid, and increase creatinine clearance rate and improve the total effective rate of symptoms and signs. However, there is no evidence that rhubarb is more effective than the control group in increasing hemoglobin. In addition, due to the low quality of research methodology in the included literature, it is necessary to further study high-quality literature to evaluate its efficacy and safety.
In patients with chronic renal failure, retention enema therapy using rhubarb has been shown to delay renal function deterioration and improve proteinuria indicators.
Proposed mechanisms. In vivo studies have shown that rhubarb markedly decreased renal functional impairment and attenuated renal fibrosis. A clinical trial showed that rhubarb is able to reduce proteinuria and improve renal function by itself, and it may also have positive cumulative effects when combined with angiotensin-converting enzyme inhibitors.
Evidence strength. Current clinical studies still face limitations such as small sample sizes, inconsistent efficacy evaluation criteria, and insufficient long-term safety data. Therefore, large-scale, multicenter, randomized controlled trials are urgently needed. Overall evidence is promising but remains preliminary-to-moderate, with most trials originating from China.
4.3 Menopausal Symptoms (Rhapontic Rhubarb, ERr 731®)
Clinical evidence. ERr 731 was effective in decreasing the number and severity of hot flushes in a 12-week multicenter trial that included 109 women with climacteric complaints, in a menopause rating scale total score given after 6 months of treatment in 252 women, as well as in 112 perimenopausal women with menopausal symptoms followed for 12 weeks.
The efficacy of ERr 731®, a commercially available extract isolated from Rheum rhaponticum, in terms of menopausal complaints like hot flushes, depression, anxiety, and vaginal dryness has been proven in a two-year clinical study. It has been described to be effective in the relief of menopausal symptoms in a 12-week double-blind, placebo-controlled trial in 109 perimenopausal women, where the total score of the Menopause Rating Scale II (MRS) was found to be significantly reduced compared to the placebo group.
Systematic review. A current systematic review provides evidence that ERr 731® supplementation is effective in reducing menopause symptoms; however, potential bias and high heterogeneity in the results warrant further clinical studies.
Post-marketing data. Post-marketing surveillance data from Germany (140 million daily doses), the United States, and Canada (13 million) suggest that the extract is generally safe for consumption.
Evidence strength. For ERr 731® specifically, evidence from multiple RCTs and a systematic review supports efficacy for menopausal symptom relief. However, these findings apply specifically to this standardized Rheum rhaponticum extract and cannot be generalized to all rhubarb root preparations.
4.4 Acute Pancreatitis
Clinical evidence. Studies from clinical trials have shown that rhubarb has a beneficial effect on patients with severe acute pancreatitis (SAP) for significant improvement of gastrointestinal function and inhibition of systemic inflammation. It may also reduce excess blood levels of pancreatic enzymes and pancreatitis events caused by some procedures. Other initial studies suggest it can treat mouth sores or help reduce radiation side effects. Additional studies are needed to determine safety and effectiveness.
Proposed mechanisms. Rhubarb inhibits the inflammatory response, improves intestinal microcirculation, and restores normal intestinal absorption, exerting a function in treating acute pancreatitis. Rhubarb markedly protects pancreatic acinar cells from trypsin-induced injury by inhibiting the synthesis, secretion, and release of trypsin in rats. Furthermore, rhubarb reduces the permeability of the capillaries, inhibits the release of inflammatory cytokines and oxygen free radicals, promotes intestinal goblet cell hyperplasia, and improves microcirculation of intestinal mucosa.
Evidence strength. All retrieved articles on this topic were from China. Therefore, there is no evidence for the application of rhubarb in other races, and the evidence may lack generalizability. Evidence remains preliminary and geographically limited.
4.5 Gastrointestinal Bleeding
Rhubarb has a hemostatic effect and is used to treat gastrointestinal bleeding clinically. It has been used for upper gastrointestinal bleeding, though most of these conditions are not supported by well-controlled trials. Evidence in this area is largely from observational and historical clinical reports.
4.6 Sepsis and Critical Illness
In septic patients, treatment with rhubarb leads to significant reductions in pro-inflammatory cytokines IL-6 and TNF-α, with marked alleviation of clinical symptoms. In a study among patients with septicemia, crude rhubarb extract powder 9 g daily was used to preserve GI function; the investigators suggest that increased perfusion of gastric mucosal blood flow, increased excretion of bacteria and toxins, and decreased permeability of intestinal mucous membranes contributed to the positive effects. These findings are preliminary and from small studies.
4.7 Anticancer Activity
Rhubarb acts as a stimulant laxative, but has not been shown to treat or prevent cancer. While compounds in rhubarb called anthraquinones reduced pain, inflammation, and some tumors in lab animals, current evidence is restricted to preclinical (in vitro and animal) models. No robust human clinical trials support anticancer use of rhubarb root.
4.8 Topical Use (Herpes and Oral Mucosa)
Rhubarb has been used topically for conditions such as herpes infections and gingivitis. An open study in adults with mild canker sores showed that topical application of a product containing 5% rhubarb extract and salicylic acid reduced the symptom resolution time by about 3 days compared with a water control. Evidence for topical use is limited to small or open-label studies.
5. Body Systems and Health Areas
- Gastrointestinal system: Rhubarb's chemical compositions show extensive pharmacological activities including regulating gastrointestinal, antimicrobial, hepatoprotective, and anti-inflammatory effects. Its laxative use for constipation is the best-established application.
- Renal system: Rhubarb has been used to treat chronic renal failure and diabetic nephropathy.
- Hepatic system: Rhubarb has the capacity to scavenge free radicals, lower liver MDA level, enhance total antioxidant capacity (T-AOC), improve antioxidant damage, reduce lipid peroxidation, stabilize cell membranes, and thus benefit hepatocytes.
- Endocrine/reproductive system: The registered special extract ERr 731® is administered to alleviate menopause-related complaints.
- Cardiovascular system: R. palmatum plays the roles of anticoagulation and antithrombosis agent and improves microcirculation through lowering endotoxin-induced permeability of microvascular tissue.
- Immune/inflammatory system: Anthraquinones such as emodin and chrysophanol display diverse pharmacological effects through anti-inflammatory and antifibrotic mechanisms, suggesting their potential as multi-target therapeutics.
- Skin (topical): Several clinical studies have demonstrated that topical application of herbal formulas containing R. palmatum L. exhibited therapeutic effects against psoriasis by alleviating the disease severity.
6. Dosage Forms and Dosages Reported in Studies
Standardized anthraquinone-based preparations (laxative use). The German monograph of Rhei radix indicates a daily dose of 20–30 mg of hydroxyanthracene derivatives calculated as rhein. According to European Medicines Agency (EMA) monographs, the maximum dosage of hydroxyanthracene derivatives should not exceed 30 mg/day in medicinal products used as a laxative for adults, elderly patients, and adolescents over 12 years. For tea infusion: 20 to 30 mg of anthranoids per day is sufficient for the laxative effect, prepared from 1 to 2 g of coarsely powdered rhubarb root, taken in the evening before bedtime.
CKD trial dosage. In one randomized clinical trial in CKD stages 3 and 4, the rhubarb group received a rhubarb capsule (350 mg, three times daily) for 12 weeks alongside conservative management.
Septicemia study dosage. In a study among patients with septicemia, crude rhubarb extract powder 9 g daily was used to preserve GI function.
ERr 731® (menopausal use). The human equivalent dose for the middle dose used in ovariectomized rat studies was estimated at 0.16 mg/kg/day, or 10 mg/day of ERr 731 extract for an average adult.
Preparation and onset of action. Standardized medicinal preparations typically work in about 8 to 12 hours, which is why bedtime use is common. Usually it is sufficient to take such preparations two to three times a week.
7. Safety Considerations and Drug Interactions
7.1 General Safety Profile
No hepatotoxicity in humans has been reported for rhubarb, though its most prevalent side effects are diarrhea and constipation. Increasing evidence has demonstrated the potential toxicity of rhubarb, including hepatotoxicity, nephrotoxicity, cardiotoxicity, and neurotoxicity, primarily from preclinical and in vitro investigations.
7.2 Hepatotoxicity
Anthraquinone compounds, especially emodin and rhein in rhubarb, are prone to causing liver damage at high doses. One study showed that rats receiving 10 g/kg for 12 weeks and 14.7 g/kg for 12 weeks (intraperitoneal injection) of rhubarb showed hepatoprotective effects, while 20 g/kg for 3 weeks and 32 g/kg for 5 days (by gavage) exhibited hepatotoxic effects, indicating that dose control is an important factor. Emodin-type anthraquinones have been recognized to have potential hepatotoxicity; electrophilic intermediates produced by emodin, aloe-emodin, and rhein have been proven to damage the mitochondria and cause hepatocyte apoptosis in vitro.
7.3 Nephrotoxicity
Anthraquinones are the active components in the root and rhizome of rhubarb and have some toxic concerns. Despite positive in vitro results for genetic toxicity, results from in vivo studies in rodents showed lack of mutagenic activity. However, the nephrotoxicity of anthraquinones has been revealed through both in vitro and in vivo studies. Some studies have suggested that the nephrotoxicity of rhubarb is not purely dose-related, but that compositional factors are equally important. The order of nephrotoxicity of the main chemical components is: aloe-emodin > rhein > emodin > chrysophanol; therefore, the nephrotoxicity of rhubarb is greatly reduced after concoction.
7.4 Adverse Effects of Prolonged Laxative Use
The EMA monograph warns that long-term use of stimulant laxatives should be avoided because it can impair normal bowel function, contribute to electrolyte imbalance, and increase dependence on laxatives. A prolonged ingestion of rhubarb root can lead to problems with the water and electrolyte balance, especially potassium loss. Protein and blood may appear in the urine (proteinuria, hematuria). Chronic use leads to (reversible) pigment deposition in the intestinal mucosa.
Prolonged use of laxatives should be avoided, as it may have a detrimental effect on the intestinal mucosa, leading to a condition known as melanosis coli, usually seen after at least 9–12 months of regular stimulant laxative use.
7.5 Contraindications
Contraindications include intestinal obstruction or stenosis, inflammatory bowel disease, unexplained abdominal pain, severe dehydration, pregnancy, breastfeeding, and use in children under 12. Rhubarb root should not be taken for intestinal obstruction, appendicitis, inflammatory bowel disorders (e.g., Crohn's disease, ulcerative colitis), abdominal pain of unknown origin, and severe dehydration symptoms.
7.6 Leaf vs. Root Toxicity
The leaf blades (but not the stalks) of rhubarb contain enough oxalic acid to cause poisoning. Acute renal failure has been associated with long-term anthraquinone use.
7.7 Drug Interactions
Cardiac glycosides and antiarrhythmic drugs. Chronic use of rhubarb root (laxative abuse) can increase the impact of digitalis drugs (cardiac glycosides) by inducing potassium deficiency; the effect of antiarrhythmic drugs may also be affected.
Diuretics and corticosteroids. Simultaneous use of thiazide diuretics, adrenal corticosteroids, and licorice root can further enhance the loss of potassium.
Warfarin. Rhubarb can work as a laxative; in some people it can cause diarrhea. Diarrhea can increase the effects of warfarin and increase the risk of bleeding. If taking warfarin, excessive amounts of rhubarb should not be taken.
Other stimulant laxatives. Taking rhubarb along with other stimulant laxatives could speed up the bowels too much and cause dehydration and low mineral levels. Such stimulant laxatives include bisacodyl, cascara, castor oil, and senna.
Renal drug transporters. Rhubarb anthraquinones inhibit human organic anion transporters hOAT1 and hOAT3. Furthermore, rhein might cause drug–drug interactions when co-administered with substrates of OAT1 or OAT3 in vivo.
Overall evidence context. Most reported clinical trials of rhubarb have been small and poorly designed; in some studies, a number of different herbs were co-administered with rhubarb, making it difficult to evaluate which herb contributed to the outcomes.
References
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