Cascara Sagrada

Kew’s POWO accepts Frangula purshiana (DC.) A.Gray ex J.G.Cooper, published in 1857, in the buckthorn family, Rhamnaceae. Its basionym is Rhamnus purshiana DC., published by de Candolle in 1825, and POWO lists Rhamnus alnifolia Pursh as a further synonym. The World Health Organization (WHO), in its 2002 monograph, lists Frangula purshiana as a synonym of Rhamnus purshiana and notes that the British, French, German, and European pharmacopoeias spelled the species purshianus, although purshiana is the correct form; that is why regulatory documents and labels still say Rhamnus while botanical databases say Frangula. POWO gives the native range as British Columbia, Washington, Oregon, California, Idaho, Montana, and northeastern Mexico, and it recognizes three subspecies: purshiana, annonifolia, and ultramafica. The US Forest Service’s Fire Effects Information System (FEIS) describes the core range as running from British Columbia to northern California, mostly west of the Cascade Range, reaching east into northern Idaho and northwestern Montana. FEIS records the common names cascara buckthorn, bearberry, chittam bark, and coffee-tree, and WHO adds bitter bark, chittem bark, and sacred bark.

Cascara is a deciduous tall shrub or small tree. FEIS describes it as up to 10 m tall, and west of the Cascades it often forms a single trunk 20–30 cm thick and 6 to about 11 m high. WHO describes reddish-brown bark and hairy twigs. The leaves are oblong to elliptical, 7.5–12.5 cm long according to FEIS, finely toothed or sometimes smooth-edged, dull green above and downy beneath, with 10 to 15 pairs of prominent, nearly parallel veins (FEIS counts 10–12) that make the tree easy to recognize; its leaf buds have no protective scales. Small greenish-yellow flowers, with petals 3–4 mm long, grow in clusters in the leaf axils, and they ripen into purplish-black drupes about 7.5–8 mm long, each with three seeds, which birds disperse. FEIS calls cascara very shade tolerant and an indicator of moist sites, often growing with red alder. It also sprouts back from the stump after the tree is felled, a trait that later mattered greatly for its survival.

The medicinal part is the dried bark. WHO describes it as quills or flattish pieces 1–5 mm thick, brown to purplish on the outside and usually patched with whitish lichens and mosses, with a bitter, nauseating, persistent taste; the inner surface turns red with dilute alkali, a classic identity test. EMA’s assessment report cites the European Pharmacopoeia standard of at least 8.0% hydroxyanthracene glycosides, at least 60% of which must be cascarosides, both calculated as cascaroside A. Cascarosides make up 60–70% of this anthranoid complex, aloins A and B and the related chrysaloins 10–30%, and O-glycosides of aloe-emodin, chrysophanol, emodin, and physcion 10–20%. Cascaroside A (PubChem CID 442727) has the formula C27H32O14. The aloins are the same compounds found in aloe latex, and EMA’s 2008 assessment grouped cascara, frangula, and aloe together as anthrone-type laxatives, distinct from senna. In fresh bark the anthranoids are present in a reduced form; WHO explains that they are converted to oxidized glycosides during drying and storage, which is why the bark must be aged before use.

Long before it had a Spanish name, cascara was medicine for the peoples of the Northwest coast and interior. Ethnobotanist Nancy Turner (BC Journal of Ecosystems and Management 2001) writes that First Peoples in British Columbia used it as a tonic and laxative, probably for thousands of years. The Native American Ethnobotany Database records laxative uses by many nations, including the Bella Coola, Cowlitz, Haisla, Klallam, Kwakiutl, Lummi, Makah, Nitinaht, Okanagan-Colville, Quileute, Quinault, Shuswap, Skagit, Squaxin, and Swinomish. The Hesquiat said the bigger the tree, the stronger the medicine, taking thick bark for a strong dose and thin bark from young trees for a mild one, and the Makah mixed it with crab apple bark. FEIS adds that the Kootenai and Flathead drank a bark tea and believed that bark stripped downward would purge while bark stripped upward would cause vomiting, and that berry juice mixed with alum made a green dye. EMA’s assessment report notes that a cascara, probably the related Rhamnus californica, was known to early Mexican and Spanish priests in California, and both EMA and the forester John Davidson (1942) explain the name as Spanish for “sacred bark.”

King’s American Dispensatory (1898) says the bark had long been known in domestic practice among western settlers as a mild cathartic before the Eclectic physician J. H. Bundy praised it in a Detroit publication in 1877, after which the Parke, Davis company introduced a fluid extract to the medical profession. By 1898 it was an official drug of the US Pharmacopeia, and EMA dates its use in Europe to about 1880. Pharmacists soon learned that fresh bark gripes and causes vomiting: the Dispensatory of the United States (1918) records the British Pharmacopoeia rule that bark be collected at least a year before use. Demand was enormous. The 1918 Dispensatory put the annual harvest at three to four million pounds and noted cultivation experiments by the US Department of Agriculture because wild sources were being rapidly destroyed. Davidson calculated that each tree yielded about 10 pounds of bark, so some 300,000 trees were destroyed each year, and cited a 1940 estimate that 90% of the original coastal stand in British Columbia had been stripped. Stripping standing trees killed them, whereas felled trees resprout, and a 1942 British Columbia order required permits, felling before peeling, and stumps at least six inches high.

Modern regulators have treated cascara more cautiously than its long history might suggest. EMA’s assessment report records Germany’s Commission E monograph of 1993, ESCOP and WHO monographs, and German pharmacovigilance measures on anthranoid laxatives that began in 1996. In June 1998 the FDA asked manufacturers for genotoxicity and carcinogenicity data on aloe and cascara; its final rule of 9 May 2002 noted that no comments or data were submitted for either, while data had arrived for senna and bisacodyl, so cascara was dropped from the over-the-counter laxative monograph. The rule affected about 160 US laxative products containing cascara ingredients, including about 125 that combined casanthranol, a cascara extract, with the stool softener docusate. EMA adopted its first cascara monograph in 2007 and a revision in 2020, and in 2022 reviewed new genotoxicity data without changing it. In the EU food sector, Regulation (EU) 2021/468 placed preparations of cascara and frangula bark under Union scrutiny while banning emodin and aloe-emodin. The EU General Court annulled those entries on 13 November 2024; on 10 September 2026 Advocate General Ćapeta advised the Court of Justice to set those judgments aside, and its final ruling is still awaited.

Cascara works like senna, through a prodrug delivered to the colon. EMA’s monograph explains that cascarosides A and B are mixed C- and O-glycosides, and that these glycosides are neither split nor absorbed in the upper gut. In the colon, bacteria convert them to emodin-9-anthrone, the main active metabolite. WHO describes the resulting action as twofold and similar to senna’s. First, it stimulates the muscle of the colon, speeding propulsion and shortening the time stool spends there, which leaves less time for water to be reabsorbed. Second, it changes how the colon lining handles salt and water, reducing absorption and promoting secretion of water and electrolytes into the bowel, which softens the stool. Because all this depends on reaching the colon and on gut bacteria, the effect is delayed: EMA says defecation follows after 8 to 12 hours, which is why doses are taken at bedtime. In animal work cited by EMA, nitric oxide produced by the enzyme iNOS appeared to be involved in cascara’s effect, and in a volunteer study 54 mg of cascaroside A made the gallbladder contract.

The ageing rule has a chemical basis. WHO’s 2018 guidelines on good herbal processing practices state that cascara bark should be aged for at least one year, or heated to speed the process, so that reduced anthranoids are converted into milder oxidized forms that cause less vomiting and stomach upset; EMA likewise attributes the emetic effect of fresh bark to its mono-anthrones. Some of the active compounds are absorbed. EMA notes that urine may turn yellow or red-brown depending on its acidity, which is harmless, and WHO adds that anthranoid metabolites can cause false-positive results in urobilinogen tests. Beyond the bowel, MSKCC reports that emodin and aloe-emodin show anticancer activity in laboratory studies, but that no human trials exist, and that emodin inhibits P-glycoprotein, a drug transporter, in laboratory and animal studies, with unknown clinical relevance. Those findings do not make cascara a cancer treatment; MSKCC lists it as an ingredient of the Hoxsey herbal formula, which it describes as ineffective.

Whether these anthranoids pose a long-term cancer risk is the central safety question, and experts disagree. EMA’s monograph reports that several hydroxyanthracene derivatives, including emodin and aloe-emodin, showed genotoxic effects in test-tube systems, but that this has not been proven in living animals. In rats, cascara bark at 140 or 420 mg/kg for 13 weeks did not produce precancerous aberrant crypt foci or tumors in the colon, although a diet containing 0.1% cascarosides increased the number of abnormal crypts per focus after a chemical carcinogen. EMA’s 2022 addendum reviewed newer comet assays of aloe-emodin, one inconclusive and one negative, and kept the monograph and its contraindications unchanged until genotoxicity is ruled out. The European Food Safety Authority (EFSA) took a stricter line in 2018, concluding that aloe-emodin is genotoxic in living animals, that hydroxyanthracene derivatives should be regarded as genotoxic and carcinogenic unless shown otherwise, and that no safe daily intake could be set. WHO’s 2002 monograph noted that no causal link between anthranoid laxatives and colorectal cancer had been demonstrated, and EMA’s 2008 report found the epidemiological studies inconsistent.

Short-term relief of occasional constipation is cascara’s only accepted modern use. EMA’s 2020 monograph lists it as a well-established use for adults, the elderly, and adolescents over 12, and adds that stimulant laxatives should be used only if a change of diet or a bulk-forming laxative has not worked. WHO’s 2002 monograph likewise lists short-term treatment of occasional constipation, and records folk uses for diabetes and, externally, for skin irritation as unsupported by experimental or clinical data. Older pharmacopoeias also described it as a cathartic, a stronger purge (WHO). Cascara has been tested as part of bowel cleansing before examinations, but EMA’s assessment report notes that a cascara-based bowel preparation performed worse than polyethylene glycol, a standard modern bowel-cleansing solution. EMA judges the benefit-risk balance positive for short courses, and it limits use to one week, usually taking the laxative two or three times in that week, because of concerns about misuse and genotoxicity.

The clinical evidence is thin. EMA’s 2020 assessment report states that no controlled clinical studies of cascara are available, that the clinical data it found involved combination products, and that there are no data in children. Instead, EMA based its decision on pharmacological data, expert opinion, long clinical experience, and evidence from senna and aloe, which share the same mechanism. The single-herb trial described in EMA’s 2008 assessment, by Mauracher in 1976, compared a cascara extract with glucofrangulin and bisacodyl in 47 mostly elderly patients in a crossover design; all three performed similarly in moderate constipation, but the dose was not reported and the gap between treatments was only two days. LiverTox cites a 2010 review by Mueller-Lissner and Wald that found no randomized controlled trial evidence for cascara in chronic constipation.

Senna is the natural comparison, and on evidence it wins. In a 2021 trial in the American Journal of Gastroenterology, Morishita and colleagues randomized 90 adults with chronic constipation to senna, magnesium oxide, or placebo for four weeks; 69.2% improved on senna, 68.3% on magnesium oxide, and 11.7% on placebo. The 2023 guideline of the American Gastroenterological Association and American College of Gastroenterology (AGA–ACG) gives senna a conditional recommendation, but cascara was not among the stimulant laxatives it reviewed, which were bisacodyl, sodium picosulfate, and senna. EMA treats the two herbs alike in dose, one-week limit, and contraindications, but its 2008 assessment suggested that anthrone-type laxatives such as cascara, frangula, and aloe were less appropriate than senna for sensitive groups. Senna also remains an over-the-counter laxative in the US, whereas cascara does not. For someone who needs an occasional stimulant laxative, senna is better studied and better regulated; cascara offers no demonstrated advantage.

Cascara’s availability as a dietary supplement invites uses it is not suited for. Many “cleanse” and slimming products rely on stimulant laxatives, but Roerig and colleagues (Drugs 2010) explain that laxative misuse for weight control rests on the false belief that diarrhea prevents calories from being absorbed, that people with eating disorders make up the largest group of laxative abusers, with misuse reported in 10–60% of them, and that abuse can cause dangerous fluid, electrolyte, and acid–base disturbances. EMA’s 2008 report notes that cascara has also been misused to try to end pregnancies, which is dangerous and one more reason it is contraindicated in pregnancy. Claims about cancer rest on laboratory studies of emodin and aloe-emodin, not on any human evidence, according to MSKCC. Cascara has no established role in chronic constipation, irritable bowel syndrome, or bowel cleansing, and anyone who feels they need a laxative every day should have the cause investigated, as EMA advises.

EMA’s monograph doses cascara by its content of hydroxyanthracene derivatives, calculated as cascaroside A: 10–30 mg once daily at night, using the smallest dose that produces a soft-formed stool, for adults, the elderly, and adolescents over 12. Products should allow doses below the maximum, and an herbal tea may contain up to 30 mg in 150 ml of boiling water. WHO lists cut and powdered bark, dried extracts, and fluidextracts among the dosage forms, and EMA’s assessment report notes that the European Pharmacopoeia’s standardized dry extract contains 8–25% hydroxyanthracene glycosides, and that a German tea product used 0.45 g of bark in 150 ml. WHO’s 2002 monograph gives 0.3–1.0 g of crude bark a day, or preparations providing 20–30 mg of hydroxyanthracene derivatives, taken at bedtime or split between morning and bedtime, and LiverTox describes a typical supplement dose of 300 mg once daily. Use should not exceed one week, and EMA notes that two or three doses in that week are usually enough.

In the United States, the FDA’s 2002 rule means casanthranol, cascara bark, cascara extract, cascara fluidextract, and aromatic cascara fluidextract can no longer be marketed as active ingredients in over-the-counter laxative drugs. The rule suggested that combination products containing casanthranol and docusate be reformulated, for example with sennosides or sodium carboxymethylcellulose. MSKCC notes that cascara is still marketed as a dietary supplement, but EMA’s dosing standard does not apply to US supplements, so check whether the label states the bark weight or hydroxyanthracene content and the plant part. Use only commercially dried and aged bark: WHO’s monograph says fresh bark must be dried for at least a year or artificially aged before therapeutic use, and that fresh bark may cause severe vomiting.

Practical points: try more fiber and fluid first, and if a stimulant is needed, consider whether a better-studied option such as senna would do. If you use cascara, take the lowest dose at bedtime with water, expect a result the next morning, and do not take another dose because nothing happened by evening. Stop if you get painful cramps or watery diarrhea, use it for no more than a week, and do not combine it with senna, aloe latex, frangula, rhubarb root, or bisacodyl, since stacked stimulant laxatives multiply cramping and potassium loss. Keep it away from children. Harvesting your own is not advisable: dosing is unpredictable and fresh bark is emetic, and Davidson’s history shows that stripping bark from standing trees kills them; a 1942 British Columbia order required trees to be felled before peeling so that stumps could resprout, and Turner notes the species has recovered over much of its range but is still rare in places.