Rhubarb

Western practice values rhubarb root for its action in both directions on the bowel. Small doses were given as a stomachic and tonic for weak, sluggish digestion ^{26Reference 26Grieve · 1931A Modern Herbal — Rhubarbs. https://botanical.com/botanical/mgmh/r/rhubar14.htmlView study →}.

Larger doses act as a brisk purgative. After the purge, an astringent after-effect checks diarrhoea, so rhubarb was also given for diarrhoea caused by an irritant in the bowel ^{26Reference 26Grieve · 1931A Modern Herbal — Rhubarbs. https://botanical.com/botanical/mgmh/r/rhubar14.htmlView study →}. In the early 1920s, acute bacillary dysentery in colonial Kenya was treated almost entirely with powdered rhubarb ^{26Reference 26Grieve · 1931A Modern Herbal — Rhubarbs. https://botanical.com/botanical/mgmh/r/rhubar14.htmlView study →}.

Eclectic and folk practice used the same root to bind or to purge according to dose, and as a gentle liver and digestive stimulant in sluggish, congested states ^{27Reference 27Hoffmann · 2003Medical Herbalism: The Science and Practice of Herbal Medicine}.

Rhubarb root is Dà Huáng (大黄), “great yellow”, one of the strongest purgatives in the Chinese materia medica.

It purges heat and accumulation, loosens the bowels, drains fire, and moves blood, removing blood stasis ^{28,29Reference 28Yang et al. · 2013Introduction to Chinese Materia Medica (3rd ed., ppReference 29Wu · 2005An Illustrated Chinese Materia Medica}.

As a purgative it is used for constipation from heat or accumulation in the intestines, with abdominal pain. As a heat-clearing, blood-cooling herb it is used for damp-heat jaundice, bleeding from heat in the blood, red eyes, sore throat, intestinal abscesses, swellings, sores and ulcers ^{28Reference 28Yang et al. · 2013Introduction to Chinese Materia Medica (3rd ed., pp}.

Processing changes the herb. Rhubarb steamed with wine is a gentler laxative than the raw root ^{31Reference 31Zhou et al. · 2024AnimalBidirectional regulation effect of rhubarb as laxative and astringent by metabolomics studies — mouse, in vivoView study →}.

Three meta-analyses of randomized trials each found that adding crude rhubarb to conventional therapy improved outcomes in acute pancreatitis.

With a trypsin inhibitor, it lowered mortality and shortened hospital stay across 16 RCTs with 912 patients ^{1Reference 1Hu et al. · 2018Meta-analysisRhubarb combined with trypsin inhibitor for severe acute pancreatitis: A systematic review and meta-analysis — systematic review, meta-analysis of RCTsView study →}.

With somatostatin, it cut total complications (risk ratio 0.55) and APACHE II scores and shortened hospital stay across 19 RCTs with 1,161 patients. Mortality did not differ ^{2Reference 2Zhou et al. · 2016Meta-analysisAdd-on effect of crude rhubarb to somatostatin for acute pancreatitis: A meta-analysis of randomised controlled trials — meta-analysis, RCTView study →}.

With early enteral nutrition, it shortened intensive-care and hospital stay across 11 RCTs with 724 patients. Mortality, infection and organ failure did not differ ^{3Reference 3Chen et al. · 2020Meta-analysisMeta-analysis of efficacy of rhubarb combined with early enteral nutrition for the treatment of severe acute pancreatitis — meta-analysis, RCTView study →}.

In a single trial of 126 patients, the group given rhubarb with early enteral nutrition recovered bowel function fastest and had the shortest intensive-care stay, with lower IL-6 and C-reactive protein ^{4Reference 4Wan et al. · 2014RCTEfficacy of rhubarb combined with early enteral nutrition for the treatment of severe acute pancreatitis: a randomised controlled trial — randomised, RCTView study →}.

The rhubarb was always an add-on, given as a decoction or through a feeding tube. Nearly all the trials are Chinese, and the meta-analyses rated their quality as low.

Gap: No trial tests rhubarb against placebo alone or as the only treatment, and trial quality (blinding, allocation concealment) is generally low, so the effect size is likely inflated.

Rhubarb’s anthraquinones, chiefly rhein, emodin and aloe-emodin, occur free and as glycosides such as sennoside A. Once bacteria in the large intestine release them, they speed colonic transit and reduce the absorption of water and salts, while increasing their secretion into the bowel. The effect appears after 8–12 hours ^{30Reference 30European Medicines Agency · 2020ReviewEuropean Union herbal monograph on Rheum palmatum L. and Rheum officinale Baillon, radix, RevView study →}.

In rat intestinal tissue, an ethanol extract of R. palmatum changed ion transport, acting on chloride movement more directly than on sodium ^{6Reference 6Tsai et al. · 2004AnimalEffect of ethanol extracts of three Chinese medicinal plants with laxative properties on ion transport of the rat intestinal epithelia — animal, in vivoView study →}.

In a 30-day double-blind, placebo-controlled trial, a rhein-standardised rhubarb extract at 12.5 or 25 mg rhein a day improved stool frequency and consistency. The volunteers were 95% women with an average age of 58. The extract was safe at the higher dose and increased butyrate-producing gut bacteria ^{5Reference 5Neyrinck et al. · 2022RCTConstipation mitigation by rhubarb extract in middle-aged adults is linked to gut microbiome modulation: A double-blind randomised placebo-controlled trial — randomised, placebo-controlled RCTView study →}.

Large doses purge, and the astringent after-effect then checks the bowel ^{26Reference 26Grieve · 1931A Modern Herbal — Rhubarbs. https://botanical.com/botanical/mgmh/r/rhubar14.htmlView study →}. In mice, raw rhubarb was laxative at first and astringent after prolonged use ^{31Reference 31Zhou et al. · 2024AnimalBidirectional regulation effect of rhubarb as laxative and astringent by metabolomics studies — mouse, in vivoView study →}.

The one oral trial was small and mostly female, and there are no head-to-head trials against standard laxatives.

A systematic review and meta-analysis of 25 animal studies found that rhein improved blood glucose, serum creatinine, urine protein, kidney damage and kidney fibrosis in models of diabetic kidney disease. The authors cautioned that publication bias and study quality may inflate the findings ^{8Reference 8Hu et al. · 2019Meta-analysisA significant association between rhein and diabetic nephropathy in animals: A systematic review and meta-analysis — systematic review, animal modelView study →}.

In mice with adenine-induced chronic kidney disease, rhein restored the kidney protein Klotho by reversing methylation of its gene promoter, protecting both kidney and bone ^{9Reference 9Zhang et al. · 2017AnimalRhein reverses Klotho repression via promoter demethylation and protects against kidney and bone injuries in mice with chronic kidney disease — mouse, in vivoView study →}. Rhein is used clinically to treat diabetic kidney disease ^{9Reference 9Zhang et al. · 2017AnimalRhein reverses Klotho repression via promoter demethylation and protects against kidney and bone injuries in mice with chronic kidney disease — mouse, in vivoView study →}.

In a randomized trial in 29 cats with naturally occurring chronic kidney disease, Chinese rhubarb (R. officinale), benazepril, or both were given for an average of 22 months. None of the groups differed in kidney function, weight, urine protein or blood pressure ^{10Reference 10Hanzlicek et al. · 2014RCTThe effect of Chinese rhubarb, Rheum officinale, with and without benazepril on the progression of naturally occurring chronic kidney disease in cats — randomised controlled trial (veterinary)View study →}.

A registered human trial of rhubarb with an ACE inhibitor for diabetic kidney disease was terminated (NCT00672451).

Gap: No completed human RCT demonstrates a renal benefit; the strongest data are animal models and an isolated constituent (rhein) rather than the whole herb.

In rats with severe acute pancreatitis and lung injury, emodin lowered the level of exosomes released from the pancreas. Exosomes from emodin-treated rats caused less inflammation in lung macrophages, acting through NF-κB and PPARγ ^{11Reference 11Hu et al. · 2022AnimalEmodin attenuates severe acute pancreatitis-associated acute lung injury by suppressing pancreatic exosome-mediated alveolar macrophage activation — rat, in vivoView study →}.

In mice with fatty liver disease, free anthraquinones from rhubarb, including rhein, emodin and aloe-emodin, inhibited the NLRP3 inflammasome and lowered IL-1β, but not TNF-α ^{15Reference 15Wu et al. · 2022AnimalRhubarb free anthraquinones improved mice non-alcoholic fatty liver disease by inhibiting NLRP3 inflammasome — mouse, in vivoView study →}.

This work is preclinical, in cells and rodents, using isolated emodin or anthraquinone fractions rather than the whole herb. No human anti-inflammatory endpoint has been measured directly.

A systematic review of 14 RCTs with 1,493 patients compared rhubarb powder solution sprayed onto the bleeding point during gastroscopy with norepinephrine solution, in acute bleeding from the upper gut not caused by varices. At 0.1 g/mL the rhubarb solution stopped bleeding more often, and it reduced rebleeding within 48 hours and caused fewer adverse reactions. At 0.03 g/mL it matched norepinephrine ^{12Reference 12Liu et al. · 2020Meta-analysisSpraying rhubarb powder solution under gastroscope in the treatment of acute non-variceal upper gastrointestinal bleeding: A systematic review and meta-analysis of randomised controlled trials — systematic review, meta-analysis, RCTView study →}.

In a retrospective, propensity-matched study of 368 critically ill patients with acute gut injury, those given rhubarb tolerated tube feeding better and spent less time in intensive care. Mortality at 28 days did not differ ^{13Reference 13Zhang et al. · 2018ObservationalEffect of rhubarb on gastrointestinal dysfunction in critically ill patients: A retrospective study based on propensity score matching — observational, cohortView study →}.

Gap: The bleeding trials use rhubarb as a locally sprayed powder during endoscopy — this does not transfer to oral or tincture use — and the critically-ill data are observational, not randomized.

In mice with fatty liver disease, free anthraquinones from rhubarb improved liver function, inflammation and fibrosis by inhibiting the NLRP3 inflammasome ^{15Reference 15Wu et al. · 2022AnimalRhubarb free anthraquinones improved mice non-alcoholic fatty liver disease by inhibiting NLRP3 inflammasome — mouse, in vivoView study →}.

In a 12-week rat study, the two lowest doses of whole R. palmatum extract reduced chemically induced liver cell injury. However, the extract increased liver fibrosis in healthy rats at every dose tested, and in injured rats at the two highest doses ^{14Reference 14Wang et al. · 2011AnimalHepatotoxicity or hepatoprotection? Pattern recognition for the paradoxical effect of the Chinese herb Rheum palmatum L. in treating rat liver injury — rat, in vivoView study →}.

In another rat study, an anthraquinone extract did not improve chemically induced liver injury at any of three doses ^{7Reference 7Li et al. · 2017AnimalPharmacokinetics and pharmacodynamics of rhubarb anthraquinones extract in normal and disease rats — animal, in vivoView study →}. The EMA notes that chronic overdose of anthranoid laxatives may lead to toxic hepatitis ^{30Reference 30European Medicines Agency · 2020ReviewEuropean Union herbal monograph on Rheum palmatum L. and Rheum officinale Baillon, radix, RevView study →}.

Gap: No human liver-endpoint trial exists, and the protective-versus-toxic threshold is defined only in rodents — so the safe therapeutic margin in people is unknown.

Emodin induces cell-cycle arrest and apoptosis across many cancer cell lines ^{16Reference 16Hsu et al. · 2012In vitroAnticancer potential of emodin — review, in vitroView study →}. Aloe-emodin at 10–80 µM triggered apoptosis and autophagy in two human pancreatic cancer cell lines ^{17Reference 17Du et al. · 2019In vitroAloe emodin exerts potent anticancer effects in MIAPaCa-2 and PANC-1 human pancreatic adenocarcinoma cell lines through activation of both apoptotic and autophagic pathways — in vitroView study →}.

These are laboratory findings for isolated molecules. There are no whole-herb or animal tumour data, and emodin can harm the kidney, liver and reproductive system at high doses over long periods ^{18Reference 18Akkol et al. · 2021ReviewIs emodin with anticancer effects completely innocent? Two sides of the coin — reviewView study →}.

An extract of R. palmatum leaves, rich in rhein, inhibited growth of the amoeba Entamoeba histolytica in the laboratory. Rhein and sennoside B were as potent as metronidazole ^{24Reference 24Espinosa et al. · 2020In vitroAnti-amebic effects of Chinese rhubarb (Rheum palmatum) leaves’ extract, the anthraquinone rhein and related compounds — in vitroView study →}.

A fraction of the root of a related species, R. undulatum, inhibited the tooth-decay bacteria Streptococcus mutans and S. sobrinus (MICs 0.25–0.5 mg/mL) and reduced plaque formation ^{25Reference 25Song et al. · 2006In vitroIn vitro anti-cariogenic activity of dichloromethane fraction from Rheum undulatum — in vitroView study →}.

There are no clinical trials of rhubarb as an antimicrobial, and neither study tested the medicinal root of R. palmatum.

In rats with intracerebral haemorrhage, a rhubarb decoction at 20 g/kg improved neurological symptoms and reduced leakage through the blood–brain barrier, while preserving the tight-junction protein zonula occludens-1 ^{19Reference 19Wang et al. · 2016AnimalRhubarb attenuates blood-brain barrier disruption via increased zonula occludens-1 expression in a rat model of intracerebral haemorrhage — animal, in vivoView study →}. It is a single animal study, not yet repeated in other models or in people.

Short-term use. Rhubarb root is a stimulant laxative, to be used for no more than a week, and only when diet or bulk-forming laxatives have not helped. Longer use can impair bowel function and lead to dependence on laxatives ^{30Reference 30European Medicines Agency · 2020ReviewEuropean Union herbal monograph on Rheum palmatum L. and Rheum officinale Baillon, radix, RevView study →}.

Potassium and drugs. Long-term use can cause loss of water and electrolytes, especially potassium. Low potassium strengthens the action of cardiac glycosides such as digoxin and interacts with antiarrhythmic drugs. Diuretics, corticosteroids and liquorice root add to the potassium loss. People taking any of these, or drugs that prolong the QT interval, should consult a doctor first ^{30Reference 30European Medicines Agency · 2020ReviewEuropean Union herbal monograph on Rheum palmatum L. and Rheum officinale Baillon, radix, RevView study →}. Faster transit may also reduce the absorption of other medicines taken at the same time.

Who should not take it. The EMA contraindicates rhubarb root in children under 12, in bowel obstruction or narrowing, in appendicitis, in inflammatory bowel disease such as Crohn’s disease or ulcerative colitis, in abdominal pain of unknown cause, and in severe dehydration ^{30Reference 30European Medicines Agency · 2020ReviewEuropean Union herbal monograph on Rheum palmatum L. and Rheum officinale Baillon, radix, RevView study →}.

Side effects. Rhubarb can cause cramping and loose stools, which call for a lower dose. It can also turn the urine yellow or red-brown, which is harmless ^{30Reference 30European Medicines Agency · 2020ReviewEuropean Union herbal monograph on Rheum palmatum L. and Rheum officinale Baillon, radix, RevView study →}.

Chronic use and the colon. Long-term use darkens the lining of the colon (melanosis coli), which usually fades after stopping ^{23,30Reference 23Yang et al. · 2020ReviewMelanosis coli: A comprehensive review — reviewView study →Reference 30European Medicines Agency · 2020ReviewEuropean Union herbal monograph on Rheum palmatum L. and Rheum officinale Baillon, radix, RevView study →}. From endoscopy data on people who had used anthranoid laxatives heavily over a long period, one analysis calculated a relative risk of colorectal cancer of 3.04 ^{21Reference 21Siegers et al. · 1993ObservationalAnthranoid laxative abuse — a risk for colorectal cancer? — review, observationalView study →}. Emodin and aloe-emodin were genotoxic in some laboratory tests, but an assessment of senna laxatives found no genotoxic risk to people at prescribed doses ^{22,30Reference 22Brusick et al. · 1997ReviewAssessment of the genotoxic risk from laxative senna products — reviewView study →Reference 30European Medicines Agency · 2020ReviewEuropean Union herbal monograph on Rheum palmatum L. and Rheum officinale Baillon, radix, RevView study →}.

Oxalate. The root contains calcium oxalate, and oxalosis has been reported with Rheum species, so it is best avoided in people prone to calcium-oxalate kidney stones ^{20,26Reference 20Barceloux · 2009ReviewRhubarb and oxalosis (Rheum species) — reviewView study →Reference 26Grieve · 1931A Modern Herbal — Rhubarbs. https://botanical.com/botanical/mgmh/r/rhubar14.htmlView study →}.

Leaves. Rhubarb leaf blades are poisonous and must never be eaten ^{20,26Reference 20Barceloux · 2009ReviewRhubarb and oxalosis (Rheum species) — reviewView study →Reference 26Grieve · 1931A Modern Herbal — Rhubarbs. https://botanical.com/botanical/mgmh/r/rhubar14.htmlView study →}.