Benefits
Bowel movement frequency and stool consistency over 30 days
In a double-blind trial in 42 middle-aged adults (95% women) with few bowel movements per week, a rhubarb root extract giving 25 mg anthraquinone derivatives a day improved stool frequency and consistency versus placebo, starting in the first week. The 12.5 mg dose improved consistency after 4 weeks. The trial was small and sponsored by the extract maker.
Herbal laxative accepted in the EU for short-term occasional use
EU herbal medicine regulators accept rhubarb root, standardized to its anthraquinone content, for short-term relief of occasional constipation in adults and adolescents. Their review found no controlled studies of the root alone and based the decision on long medicinal use, expert opinion and trials of related laxatives such as senna and aloe.
Bedtime dose with a bowel movement 8 to 12 hours later
Rhubarb root glycosides must travel to the colon and be converted by bacteria before they act, so the EU monograph advises a single dose at night and states that a bowel movement follows after 8 to 12 hours. It adds that 2 or 3 doses in a week are usually enough and that the right dose is the smallest that gives a soft, formed stool.
Butyrate-producing gut bacteria and short-chain fatty acids
In the same 30-day placebo-controlled trial, stool acetate, propionate and butyrate rose on rhubarb extract and not on placebo, but only butyrate on the 12.5 mg dose differed significantly from placebo. Lachnospiraceae bacteria such as Roseburia increased mainly on that lower dose, and higher short-chain fatty acid levels went with softer stools. These were secondary outcomes in a small trial.
Gut barrier permeability markers in one small hospital trial
In 40 hospitalized patients with sepsis, crude rhubarb powder (3 g three times daily by mouth) added to standard care was followed by a lower urine lactulose to mannitol ratio and lower blood D-lactate on day 6 than in the control group, both markers of gut permeability. The trial was small, the abstract does not describe blinding, and it was a drug-use setting.
Body weight and gut bacteria in mice on a high-fat, high-sugar diet (animal study)
In mice fed a high-fat, high-sucrose diet for 8 weeks, adding 0.3% Rheum palmatum root extract to the food prevented the weight gain, fat build-up and high blood sugar seen in untreated mice, along with a rise in the gut bacterium Akkermansia muciniphila. This was an animal study, and these effects have not been tested in people.
Mechanism of action
Activation by colon bacteria
The glycosides in rhubarb root are not split by human digestive enzymes, so little is absorbed in the upper gut. Colon bacteria convert them into active anthrones; in mouse studies rhein anthrone, the active form of the sennosides found in rhubarb and senna, was a stronger purgative than the free anthraquinones. Rhein, emodin and traces of chrysophanol then appear in human urine.
Faster colonic transit and more water in the stool
The EU monograph describes two actions of the active anthrones: they stimulate motility of the large intestine, speeding transit, and they reduce absorption of water, sodium and chloride while increasing secretion of water and electrolytes into the colon. In mice, rhein anthrone and aloe-emodin anthrone acted together on both transit and water secretion.
Tannins with an astringent effect
Rhubarb root contains about 5% gallotannins. The EU assessment notes that these tannins may partly counteract the laxative effect, so rhubarb is considered milder than other anthranoid laxatives, and older reference texts describe small doses of 0.1 to 0.3 g acting mainly as an astringent rather than a laxative.
Clinical trials
Randomized, double-blind, placebo-controlled trial at a private clinical investigation center in Dijon, France (2017 to 2018), of Rheum palmatum root extract tablets (Gutisrheum, Laboratoires Ortis) giving 12.5 mg or 25 mg hydroxyanthracene derivatives (as rhein) daily at bedtime versus maltodextrin placebo for 30 days. Sponsored by Laboratoires Ortis; registered as NCT05541991 in 2022, after completion. The registry names change in weekly bowel movements as the primary outcome and lists 45 enrolled and several gut hormone, permeability and inflammation outcomes that the paper does not report. (Neyrinck et al. 2022, Int J Mol Sci)
42 middle-aged volunteers (95% women, average age 58) with about 2.3 bowel movements per week at baseline; 13 per group were analyzed.
Stool frequency and consistency improved more on the 25 mg dose than on placebo from the first week; the 12.5 mg dose improved consistency after 4 weeks. Improved transit speed was reported by 92% on 25 mg, 62% on 12.5 mg and 23% on placebo. Stool short-chain fatty acids rose on rhubarb, but only butyrate on 12.5 mg differed significantly from placebo. Days with abdominal discomfort rose on rhubarb (by 0.2 and 2.2 days on average) and fell on placebo, and the number of people with diarrhea or loose stools rose significantly on 25 mg.
Randomized controlled trial by authors from Zhejiang University, China; both groups had the same treatment, and one group also took crude rhubarb powder 3 g three times daily by mouth. The abstract does not state blinding, the rhubarb species or funding. (Fang et al. 2007, Am J Chin Med)
40 patients with sepsis (18 given rhubarb, 22 controls).
On day 1 the groups did not differ. On day 6 the urine lactulose to mannitol ratio was 0.062 with rhubarb versus 0.167 in controls, and blood procalcitonin and D-lactate were also lower with rhubarb (P < 0.05 for each). No clinical outcomes such as survival were reported in the abstract.
Cochrane systematic review of randomized and quasi-randomized trials of Rheum officinale (da huang), with searches of English and Chinese databases to 2011 and no restriction on dose or route of use. (Wang et al. 2012, Cochrane Database Syst Rev)
9 trials with 682 participants with chronic kidney disease; 7 compared rhubarb with no treatment and 2 with captopril.
Against no treatment, rhubarb lowered serum creatinine and blood urea nitrogen, but no trial reported blinding or how groups were allocated. Against captopril there was no significant difference for any outcome, and no trial reported mortality. Only minor adverse events were reported. The reviewers judged the evidence scant and low quality and found no basis for any recommendation.
Prospective crossover study in which each volunteer received a single 50 mg/kg dose of an aqueous Rheum officinale extract (about 54 mg hydroxyanthracene derivatives for a 60 kg person, per the EU assessment) once by mouth and once as a retention enema, with plasma rhein measured by HPLC. The EU assessment of this study notes that 2 volunteers had mild to moderate diarrhea that resolved on its own. (Zhu et al. 2005, Am J Chin Med)
8 healthy male volunteers.
Peak rhein level and total exposure were significantly higher after oral dosing than after the enema, while time to peak, half-life and clearance did not differ. There was no placebo group and no laxative outcome.
Animal study in which male mice ate a control diet, a high-fat, high-sucrose diet, or the same diet with 0.3% rhubarb root extract (Ortis; 5.07% anthracene derivatives as rhein) for 8 weeks. (Régnier et al. 2020, Nutrients)
C57BL/6J male mice; no people were dosed.
The extract prevented diet-induced weight gain, visceral fat, high blood sugar, fat tissue inflammation and liver fat build-up without changing food intake, and these effects went with a large rise in Akkermansia muciniphila. Results in mice do not show the same effect in people.
Animal study in which mice ate a control diet with or without 0.3% rhubarb extract for 17 days and were examined 6 hours after an alcohol challenge; the extract also increased crypt depth, tissue weight and antimicrobial peptide expression in the gut. The same research group later identified its extract as Rheum palmatum root. (Neyrinck et al. 2017, Mol Nutr Food Res)
Mice; no people were dosed.
The extract shifted the bacterial mix toward Akkermansia muciniphila and Parabacteroides goldsteinii and lowered markers of liver inflammation and oxidative stress after alcohol, without significantly changing liver fat. This is animal work only.