GI Modifiers: Irritants

Summary

Gastrointestinal Irritant Herbs

introduction: Gastrointestinal irritation may be caused by several herbal constituents including saponins, volatile oils, some tannins, and anthraquinones. Anthraquinones are the most important irritant herbal compounds which significantly alter gastro-intestinal motility to the extent that anthraquinone containing herbs are have long been used as laxatives, cathartics and purgatives. Although anthraquinones are widely distributed, particularly high amounts are found among the Fabaceae (e.g., Cassia spp.), Polygonaceae (e.g., Rheum spp.), Rhamnaceae (e.g., Rhamnus spp.) and Lilliaceae (e.g., Aloe). The increase of gastric motility following oral ingestion of anthraquinone herbs will significantly reduce transit times, therefore potentially reducing absorption of concurrently ingested medications.

anthraquinone chemistry:
Anthraquinones are phenolic compounds based on a C6-C2-C6 ring structure whose stability is affected by extraction method and aging. There is a dynamic isomerism between anthranol and anthrone forms. Both of these are more drastic (more bioactive) compounds than the anthraquinone form. Many active plant anthraquinones are dimers (two molecules joined head to tail). They are often yellow in color and bitter to taste. They naturally exist in glycoside form, usually with glucose or rhamnose sugar moieties. Generally, the more powerful agents such as Frangula and Cascara bark are stored for a year prior to consumption: the aging process reduces the irritant activity of the herb as the anthraquinones condense to form dimers, or oxidize to the milder anthraquinone form.

The glycosides are hydrolyzed by bowel flora, and the hydrolysis is slow, resulting in a period of 8-10 hours between ingestion and softening of the stool. The mechanism of action is thought to be both local, via the "paracrine" production of prostaglandin PGE2, and systemic, through action on the neural plexi of the gut wall. Overdose of anthraquinone herbs will cause griping, and herbalists prescribe them in conjunction with carminative herbs. The presence of tannins in anthraquinone herbs may moderate the effects of the anthraquinone activity.

Examples of anthraquinones:
• Aloe-emodin: Rheum spp., Rumex spp., Aloe spp.
• Barbaloin: Rhamnus spp., Aloe spp.
• Cascarosides A-D: Rhamnus purshiana
• Chrysophanol: Rheum spp., Rumex spp.
• Emodin: Rhamnus spp
• Rhein: Rheum spp., Rumex spp., Cassia spp.
• Sennosides A-D: Cassia spp.

non-anthraquinone irritant herbs:
A number of heterogeneous herbal constituents besides anthraquinones may produce gastro-intestinal irritation: these are primarily saponins, alkaloids, tannins or volatile oils. Gastrointestinal irritation is also reported as an undesirable adverse effect in sensitive individuals consuming a variety of diverse herbal medications.

overview of pharmacokinetic interactions:
• mechanism: Anthraquinone laxative and other irritant herbs may reduce absorption of concurrently ingested medications due to increase in gut motility and reduction of transit times.

• herbal concern: Pharmaceutical medications should not be consumed concurrently with laxative or irritant herbs.

• herbal concern: pregnancy: Anthraquinone laxative herbs are commonly reported to be contraindicated in pregnancy due to their "sacral irritant" effects, but evidence of this lack of safety is not available. Cassia senna (Senna) has been shown to safe in pregnancy and lactation. Senna syrup is also used for children.
see: Herb Group: Ob/Gyn: Pregnancy and Lactation

• herbal concern: Overuse of anthraquinone laxative herbs is a continuing concern. Extended use of anthraquinone laxative herbs can lead to a vicious circle of declining bowel tonicity and continued constipation since irritant herbs do not restore atonicity; instead, repeated use will tend to make the condition worse.

• herbal synergy: Other herbs affect bowel function and may act as laxatives through mechanisms other than irritation:

See Herb Group Pharmacokinetic: GI Modifiers: Bitters
See Herb Group Pharmacokinetic: GI Modifiers: Hydrocolloids
See Herb Group Pharmacokinetic: GI Modifiers: Tannins



Herbs

Common herbs containing anthraquinones:
• Aloe spp. (Aloe)
• Cassia spp. (Senna)
• Rhamnus catharticus (Buckthorn bark)
• Rhamnus purshiana (Cascara Sagrada)
• Rheum officinale (Chinese Rhubarb)
• Rheum palmatum (Turkey Rhubarb)
• Rumex crispus (Yellow Dock)
• Tabebuia impetiginosa (Pau D'Arco)

Non-anthraquinone irritant herbs:
• Aesculus californica (Buckeye) [saponins]
• Aesculus hippocastanum (Horse Chestnut) [saponins]
• Arctostaphylos uva-ursi (Bearberry) [tannins]
• Berberis vulgaris (Barberry) [alkaloids]
• Capsicum frutescens (Cayenne) [alkaloids]
• Citrullus colocynthus (Colocynth) [cucurbitanes]
• Hydrastis canadensis (Goldenseal) [alkaloids]
• Iris versicolor (Blue flag) [volatile oil]
• Juglans cinerea (Butternut bark) [napthoquinones]
• Mahonia spp. (Oregon Grape Root) [alkaloids]
• Sanguinaria canadensis (Blood Root) [alkaloids]

Restricted or unusual irritant herbs:
• Chenopodium ambrosioides (Wormseed) [Ascaridiol - toxic]
• Ipomoea purga, syn.Convolvulus jalapa (Jalap root) [Resins- toxic]
• Podophyllum peltatum (American mandrake) [Podophyllotoxin - toxic]
• Ricinus communis (Castor Oil) [Ricinoleic Acid - toxic]

Please read the disclaimer concerning the intent and limitations of the information provided here.
Do not rely solely on the information in this article.

The information presented in Interactions is for informational and educational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, case reports, and/or traditional usage with sources as cited in each topic. The results reported may not necessarily occur in all individuals and different individuals with the same medical conditions with the same symptoms will often require differing treatments. For many of the conditions discussed, treatment with conventional medical therapies, including prescription drugs or over-the-counter medications, is also available. Consult your physician, an appropriately trained healthcare practitioner, and/or pharmacist for any health concern or medical problem before using any herbal products or nutritional supplements or before making any changes in prescribed medications and/or before attempting to independently treat a medical condition using supplements, herbs, remedies, or other forms of self-care.


References

Brinker F. Herb Contraindications and Drug Interactions. Second edition. Sandy, OR: Eclectic Institute Inc, 1998.

Duke JA. Handbook of Phytochemical Constituents of GRAS Herbs and Other Economical Plants. CRC Press, 1994.

Hoffmann D. Phytochemistry. (Forthcoming title, in press 1999, publisher to be confirmed).

Mills SY. Out of the Earth (The Essential Book of Herbal Medicine). London, UK: Arkana. 1991.

Moore M. Herbal/Medical Contraindications. Albuquerque, NM: Southwest School of Botanical Medicine, 1995.