Diarrhea

Guava leaf is one of the few traditional antidiarrheals to have been tested properly and repeatedly. A randomised open-label trial of oral guava leaf decoction in acute infectious diarrhoea found benefit ^{7Reference 7Birdi et al. · 2020RCTA randomized open label efficacy clinical trial of oral guava leaf decoction in patients with acute infectious diarrhoea — randomised controlled trialView study →}; a randomised, double-blind trial of a quercetin-standardised P. guajava leaf phytodrug (QG-5) in 50 adults with acute diarrhoeal disease reported reduced duration of abdominal pain — the trial’s reported outcome, not a measured effect on stool output ^{8Reference 8Lozoya et al. · 2002RCTIntestinal anti-spasmodic effect of a phytodrug of Psidium guajava folia in the treatment of acute diarrheic disease — randomised, double-blind clinical trialView study →}; and a 2024 systematic review of guava extract in acute diarrhoea pooled the field ^{9Reference 9Garrido et al. · 2024Systematic reviewAntidiarrheal effect of Psidium guajava L. extract in acute diarrhea — systematic reviewView study →}.

The mechanism is dual — tannins tighten inflamed mucosa and reduce secretion, while flavonoids (notably quercetin) relax intestinal smooth muscle, slowing transit.

The trials are small, several are open-label, and preparations differ between them.

A purified fraction of the sap became a prescription drug. The sap’s oligomeric proanthocyanidin (SP-303) was developed into crofelemer and tested in multiple randomised placebo-controlled trials — in travellers’ diarrhoea, where it shortened illness by 21% ^{10Reference 10DiCesare et al. · 2002RCTA double blind, randomized, placebo-controlled study of SP-303 (Provir) in the symptomatic treatment of acute diarrhea among travelers to Jamaica and Mexico — randomised controlled trialView study →}; in AIDS-related diarrhoea, where the day-4 comparison actually missed significance and only the repeated-measures analysis over four days reached it ^{11Reference 11Holodniy et al. · 1999RCTA double blind, randomized, placebo-controlled phase II study to assess the safety and efficacy of orally administered SP-303 for the symptomatic treatment of diarrhea in patients with AIDS — randomised controlled trialView study →}; and in the phase 3 ADVENT trial of non-infectious diarrhoea in HIV-seropositive adults ^{12Reference 12Macarthur et al. · 2013RCTEfficacy and safety of crofelemer for noninfectious diarrhea in HIV-seropositive individuals (ADVENT trial): a randomized, double-blind, placebo-controlled, two-stage study — randomised controlled trialView study →}, which supported FDA approval.

The mechanism is precise and unusual: it blocks two gut chloride channels (CFTR and the calcium-activated chloride channel), cutting the secretion that drives secretory diarrhea, and it is minimally absorbed — a locally acting drug, which is why its safety profile is close to placebo.

This evidence is for the standardised drug, not for drops of sap; sap chemistry varies with provenance and unrelated red-sap Croton species are sold under the same name.

Barberry’s antidiarrheal action comes from berberine, tested in an old human trial: a randomised controlled trial in 165 adults found a single 400 mg oral dose of berberine sulfate significantly reduced stool volume in enterotoxigenic E. coli diarrhoea, with 42% of treated patients free of diarrhoea at 24 hours against 20% of controls ^{13Reference 13Rabbani et al. · 1987RCTRandomized controlled trial of berberine sulfate therapy for diarrhoea due to enterotoxigenic Escherichia coli and Vibrio cholerae — randomised controlled trialView study →}.

This trial is widely miscited as showing benefit in cholera; it does not. The cholera effect was confined to a single 8-hour window, a higher 1200 mg dose added nothing to tetracycline, and the authors’ own conclusion is that activity against cholera is slight.

The effect is antisecretory — berberine acts on the same secretory mechanism crofelemer does, rather than killing the organism — which makes it mechanistically well matched to watery, toxin-driven diarrhea. The trial used isolated berberine sulfate at a defined dose, not barberry bark.

The same berberine chemistry, from the classical Chinese antidysenteric. Coptis is the herb TCM reaches for in damp-heat dysentery and gastrointestinal infection, and its best modern human data are also berberine’s: a randomised, double-blind, placebo-controlled trial of berberine hydrochloride in diarrhoea-predominant IBS found benefit ^{14Reference 14Chen et al. · 2015RCTA randomised clinical trial of berberine hydrochloride in patients with diarrhoea-predominant irritable bowel syndrome — randomised, double-blind, placebo-controlled trialView study →}. That is a different clinical problem from acute infectious diarrhea — chronic, non-infectious, motility-related — and it is not evidence for acute use. Whole-rhizome alkaloids (coptisine, epiberberine) add antimicrobial and anti-colitis activity in preclinical models.

Chamomile’s traditional use for colic, cramping and childhood diarrhea has an unusually well-defined animal mechanism. A crude aqueous-methanolic extract produced dose-dependent antidiarrhoeal, antisecretory and antispasmodic effects in mice and relaxed isolated rabbit jejunum, acting predominantly through K⁺-channel activation with a weaker calcium-antagonist component ^{15Reference 15Mehmood et al. · 2015In vitroAntidiarrhoeal, antisecretory and antispasmodic activities of Matricaria chamomilla are mediated predominantly through K⁺-channels activation — animal / in vitro studyView study →}. That covers secretion, motility and spasm together.

There is no human trial for this indication. Chamomile is mild, palatable and among the safest antidiarrheal herbs.

A widespread South American traditional remedy for diarrhoea and dysentery, with a rodent result behind it: C. pareira extract produced a dose-dependent reduction in experimentally induced (castor-oil model) diarrhoea ^{16Reference 16Amresh et al. · 2004AnimalEthnomedical value of Cissampelos pareira extract in experimentally induced diarrhoea — animal modelView study →}. The castor-oil model is a standard antidiarrheal screen. The result is a single animal study.

The astringent bark decoction was one of the most widely used antidiarrheal remedies of Indigenous North America. Its modern evidence comes from livestock research: a substantial and consistent body of animal feeding trials in poultry, pigs and ruminants shows its polyphenols modulate gut microbiota and suppress enteric pathogens ^{17Reference 17Zheng et al. · 2021AnimalDietary supplementation of red-osier dogwood polyphenol extract changes the ileal microbiota structure and increases Lactobacillus in a pig model — in vivo animal modelView study →} — in-vivo work at scale, across three species, from research aimed at livestock gut health rather than human medicine. Anti-inflammatory activity in human intestinal cell models supports it ^{18Reference 18Jiang et al. · 2019In vitroRed-osier dogwood extracts prevent inflammatory responses in Caco-2 cells and a Caco-2 BBe1/EA.hy926 co-culture model — in vitroView study →}.

The studied material is leaf and stem extract, not the traditional bark. Fresh bark is traditionally purgative — drying removes this, which is why traditional preparation specifies dried bark.

By most surveys the most-used medicinal plant in Mexico, and its core traditional indications are gastrointestinal — diarrhoea, dysentery, stomach pain and empacho. The laboratory work tracks that closely: in-vitro activity against Entamoeba and Giardia ^{19Reference 19Said-Fernández et al. · 2005In vitroIn vitro antiprotozoal activity of the leaves of Artemisia ludoviciana — in vitroView study →}, and against Fasciola ^{20Reference 20Ezeta-Miranda et al. · 2020In vitroEfficacy of purified fractions of Artemisia ludoviciana Nutt. mexicana against newly excysted juveniles of Fasciola hepatica in vitro — in vitroView study →}, plus direct smooth-muscle relaxation and a dedicated antidiarrhoeal signal.

All of this work is in vitro, and the essential oil is camphor-rich and not equivalent to the traditional infusion.

An astringent used for diarrhoea in two independent traditions — European folk practice and Tibetan plateau medicine, where the tuberous root is also a cultivated food. Its tannins are identified: the ellagitannins agrimoniin and potentillin. A 2024 systematic review catalogued 154 constituents and mapped the plant’s activity, and a maximum-feasible-dose mouse study found no acute toxicity ^{21Reference 21Li et al. · 2024Systematic reviewA systematic review on botany, ethnopharmacology, phytochemistry and pharmacology of Potentilla anserina L. — systematic reviewView study →}. There is no human trial for any indication.

One of Ayurveda’s foremost remedies for diarrhoea and dysentery. Ripeness decides its action: the unripe fruit — hard and intensely astringent, high in tannins — is the antidiarrheal, while the ripe fruit is sweet, mucilaginous and taken almost for the opposite purpose. On the strength of that reputation the unripe fruit once entered the British Pharmacopoeia. It has not been tested in a clinical trial.

Dose decides the direction. Haritaki has a genuine dose-dependent duality: at low doses the astringent tannins dominate and produce a binding, antidiarrheal effect — in TCM it is He Zi, used to “bind the Intestines” for chronic diarrhoea — while at higher doses its anthraquinone (sennoside-type) glycosides drive a laxative-to-purgative action. The wrong dose does the opposite of what is intended.

Haritaki is avoided in active diarrhoea and dehydration.

An Amazonian and Caribbean bark that entered the eighteenth- and nineteenth-century European pharmacopoeias as Simaroubae cortex, used specifically as an antidysenteric — for amoebic and bacillary dysentery, ordinary diarrhoea and intestinal parasites. There is no modern controlled trial.

The astringent leaf tea was used for diarrhoea and stomach complaints across the Pacific Northwest, alongside the berry’s role as a staple food. The plant’s measured chemistry is almost all from the fruit, while the traditional medicine is the leaf, whose tannin profile has never been characterised, so the mechanism is assumed from the family rather than demonstrated. Not to be confused with its relative G. procumbens (wintergreen), which is rich in toxic methyl salicylate.

Psyllium works by physics rather than pharmacology. The husk is a bulk-forming fibre with enormous water-holding capacity, and its traditional use in the Indian subcontinent is dual — a gentle laxative in constipation, and a stool-firming agent in diarrhoea, because adding form and slowing transit helps in both directions. The antidiarrheal use rests on tradition and mechanism rather than dedicated trials. Take with plenty of water.

A traditional Amazonian remedy for stomach complaints and diarrhoea. Its one relevant modern data point is narrow but apt: a screen of Brazilian medicinal plants found H. courbaril leaf extract active against rotavirus in vitro ^{22Reference 22Cecílio et al. · 2012In vitroScreening of Brazilian medicinal plants for antiviral activity against rotavirus — in vitroView study →} — rotavirus being a leading cause of severe childhood diarrhoea. The finding is unreplicated and in vitro.