Rhamnus purshiana (cascara buckthorn, cascara, bearberry, and in the Chinook Jargon, chittem and chitticum; syn. Frangula purshiana, Rhamnus purshianus) is a species of buckthorn native to western North America from southern British Columbia south to central California, and eastward to northwestern Montana.
The dried bark of cascara has been used for centuries as an herbal laxative – first by Native Americans in the Pacific Northwest, and then later by European/U.S. colonizers. The chemicals primarily responsible for the laxative action are the hydroxyanthracene glycosides (particularly cascarosides A, B, C and D), and emodin. These act as stimulant laxatives, with the hydroanthracene glycosides stimulating peristalsis, and emodin exciting smooth muscle cells in the large intestine.
Range and habitat 
Cascara is native from northern California to British Columbia and east to the Rocky Mountains in Montana. It is often found along streamsides in the mixed deciduous-coniferous forests of valleys, and in moist montane forests. Cascara is common in the understory of bigleaf maple forest, alongside red osier dogwood and red alder.
In many areas, the high market demand for cascara bark has led to over-harvesting from wild trees, which may have heavily reduced cascara populations.
Medicinal use 
Historical background 
The dried, aged bark of R. purshiana has been used continually for many years by both Pacific northwest native peoples and immigrant Euro-Americans as a laxative natural medicine, as one of several anthraquinone-containing herbal medicines including the leaf and fruits of senna, the latex of Aloe vera, and the root of the rhubarb plant. Commercially it is called "Cascara Sagrada" ('sacred bark' in Spanish), while traditionally it is known as "chittem bark" or "chitticum bark".
Spanish conquerors exploring the Pacific Northwest in the 1600s came across many Native peoples using the bark of R. purshiana as a laxative. They gave it the name "Sacred Bark" (cascara sagrada) in honor of its effectiveness. By 1877 the U.S. pharmaceutical company Parke-Davis was producing cascara preparations, and soon afterwards cascara products were being exported overseas to European markets. The explosion of the cascara industry caused great damage to native cascara populations during the 1900s, as a result of overharvesting.
In 1999, cascara made up more than 20% of the national laxative market in the U.S., with an estimated value of $400 million. The bark itself was worth approximately $100 million. Cascara was found in more drug preparations than any other natural product in North America, and is believed to be the most widely used cathartic in the world.
Numerous quinoid substances are found in the bark of cascara. The chemicals primarily responsible for the laxative action are the hydroxyanthracene glycosides, which includes cascarosides A, B, C, and D. Cascara contains approximately 8% anthranoids by mass, of which about two-thirds are cascarosides. The hydroxyanthracene glycosides act as a stimulant laxative by exciting peristalsis in the colon. They trigger peristalsis by inhibiting the absorption of water and electrolytes in the large intestine, which increases the volume of the bowel's contents, leading to increased pressure.
The hydroxyanthracene glycosides are not readily absorbed in the small intestine but are hydrolyzed by intestinal flora to a form that is partly absorbed in the colon. Hydrolysis of the cascarosides results in the formation of aloins such as barbaloin and chrysaloin. Some of the chemical constituents present in the bark may be excreted by the kidney following medicinal use, resulting in a harmless change in the color of the urine.
Studies have shown that the extract from cascara bark also contains a substance called emodin, which may have anti-cancer effects. Emodin is also responsible for some of the laxative effect, due to its excitation of smooth muscle cells in the large intestine.
The bark is collected in the spring or early summer, when it easily peels from the tree. Once stripped from the tree, the bark must be aged for at least 1 year before use, because fresh cut, dried bark causes vomiting and violent diarrhea. This drying is generally done in the shade to preserve its characteristic yellow color. This process can be quickened by simply baking the bark at a low temperature for several hours. In her book, Major Medicinal Plants, Dr. Julia Morton suggests using a dosage of 10–30 grains, dissolved in water, or 0.6–2 cc for fluid extract. The ethnobotanist and herbalist Dr. James A. Duke suggests an effective dosage of approximately 1 to 3 grams dried bark, or 1–2.5 grams powdered bark.
Laxative should only be used on a short-term basis (no longer than 7 days), and should not be used by pregnant woman (because cathartics such as cascara can induce labor), lactating women (because the active compounds can be transferred to the infant), or by people with intestinal obstructions or injuries. Laxative should also not be used by people with Crohn's disease, irritable bowel syndrome, colitis, hemorrhoids, appendicitis, or kidney problems.
Although chronic use of anthranoid-containing laxatives has been hypothesized to play a role in colorectal cancer, no causal relationship has been demonstrated. No specific data on carcinogenicity or mutagenicity are available for Cortex Rhamni Purshianae or the cascarosides. Data for aloin derived from aloe indicate no genotoxic risk. Emodin derived from aloe showed both positive and negative results in vitro, but was negative in vivo. Emodin was mutagenic in the Salmonella / microsome assay, but gave inconsistent results in gene mutation assays. It showed positive results in the test for unscheduled DNA synthesis with primary rat hepatocytes, but negative results in the sister chromatid exchange assay.
FDA regulation 
Cascara Sagrada was used by Native Americans for centuries, and was accepted into medical practice in the United States in 1877, and by 1890 had replaced the berries of the European buckthorn (R. catharticus) as a commonly used laxative. It was the principal ingredient in many commercial, over-the-counter laxatives in North American pharmacies until 9 May 2002, when the U.S. Food and Drug Administration issued a final rule banning the use of aloe and Cascara Sagrada as laxative ingredients in over-the-counter drug products. Use of Cascara Sagrada has been associated with abdominal pain and diarrhea; it is also potentially carcinogenic. Another study in 1999 states it is not carcinogenic. Aloe emodin one of the constituents of Cascara Sagrada, is present in Aloe Vera and may increase the carcinogenicity of some kind of radiation, but have a marked anti-viral effect in vitro against both herpes simplex virus (HSV) type 1 and 2
In July 2003, the FDA responded to a citizen's petition filed against the May 2002 final ruling banning the use of cascara sagrada in OTC laxatives  by the American Herbal Products Association (AHPA) and International Aloe Science Council (IASC) (June 2002, CP25) and subsequent data submissions that occurred in October 2002 (SUP14) and December 2002 (SUP15)). In this letter the FDA stated that the American Herbal Products Association Botanical Safety Handbook (1997), the one cited to the FDA in CP25, contained only general information similar to information they already had in 1975. Upon further evaluation of all submitted information it found inadequate support for the petition that cascara sagrada should be generally recognized as safe and effective for OTC use as a laxative.
In September 2003 the FDA also responded to a petition (CP27) that was filed in August 2002 in which the FDA stated that "the agency does not find that the benefits of using cascara sagrada laxative ingredients outweigh the risks" and that the data contained in petition CP27 "do not rule out the possibility that cascara sagrada preparations are genotoxic and/or carcinogenic."
Other uses 
The fruit can also be eaten cooked or raw, but has a laxative effect. The food industry sometimes uses cascara as a flavoring agent for liquors, soft drinks, ice cream, and baked goods. Cascara honey is tasty, but slightly laxative. The wood is used by local people for a posts, firewood, and turnery. It is also planted as an ornamental, to provide food and habitat for wildlife, or to prevent soil erosion. Due to its bitter taste, cascara can be used to stop nail-biting by applying it to the fingernails.
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