Hound's tongue

Other Names

beggar's licecommon burcommon hound's tonguecommon houndstongueCynoglosse officinalCynoglossum album Gueldenst.Cynoglossum angustifolium E.A.DuchesneCynoglossum angustifolium Steud.Cynoglossum bicolor Willd.Cynoglossum bracteolatum OpizCynoglossum castellanum PauCynoglossum foetens Gilib.Cynoglossum hybridum Thuill.Cynoglossum officinaleCynoglossum officinale L.dog burdog's tongueEchte HundezungeEchte HundszungeGebräuchliche HundszungeGemeine HundszungeGewöhnliche HundszungeGewone hondstongglovewortgypsy flowergypsyflowerHarilik rasshondstonghoundstonguehoundstoothHundetungeHundtungaKözönséges ebnyelvufuLäge-HundetungeLangue-de-chienLengua de perroLindefolia spectabilisLingua-di-cane vellutinaOstrzen pospolityrats and miceRohtokoirankieletsheelicesheep bursheep licesticktightUžanka lékarskáwoolmat

Synopsis

Hound's Tongue (Cynoglossum officinale L.): A Comprehensive Reference

1. Identity, Taxonomy, and Botanical Description

Scientific Classification and Nomenclature

Cynoglossum officinale — commonly known as houndstongue, houndstooth, dog's tongue, gypsy flower, and "rats and mice" (owing to its distinctive smell) — is a herbaceous plant of the family Boraginaceae. The genus name Cynoglossum derives from the Ancient Greek words kynōs (κύων), meaning "dog," and glōssa (γλῶσσα), meaning "tongue," alluding to the rough, tongue-like texture and shape of the plant's leaves. The specific epithet officinale is a New Latin term rooted in the Latin officina, referring to a workshop or storeroom — particularly those in monasteries or apothecaries where medicinal herbs were prepared and sold — thus denoting the plant's historical use in traditional medicine.

The primary common name, houndstongue or hound's-tongue, reflects the resemblance of the leaves to a dog's tongue and traces back to Old English hundes tunge, evolving through Middle English as houndestonge. The plant owes its common and scientific name to the long greyish leaves that are reminiscent of a dog's tongue, and it was once given as a remedy for dog bites. There is also a folk belief that it could, if a leaf was worn in the shoe, ward off dog attacks.

Morphology and Growth Habit

The species is a herbaceous plant of the family Boraginaceae and can be either annual or biennial. It is a biennial plant with an erect, silky-pubescent stem growing from 1 to 2 feet in height. The leaves are hoary, with soft down on both sides, lanceolate, acute, and entire — radical ones alternate at the base and petiolate; cauline ones sessile, clasping, with rounded or slightly heart-shaped bases. The flowers are in terminal, panicled clusters recurved at the end; the calyx is downy and 5-parted; the corolla is reddish-purple, short, funnel-form, and vaulted, with the throat or orifice closed by 5 converging, convex scales. Reddish-purple funnel-shaped flowers bloom between May and September.

Geographic Distribution and Habitat

The species is native to temperate regions of Eurasia, spanning from the Mediterranean Basin in southern Europe through eastern Europe and western Asia, extending northward to western and southern Siberia. Its distribution covers much of Europe up to approximately 60°N latitude, with isolated occurrences as far north as 68°N in Sweden, and reaches into central Asia including parts of Kazakhstan, Kyrgyzstan, and Iran. It is also found in North America, where it was accidentally introduced, including in British Columbia, where it is designated a noxious weed under the British Columbia Weed Control Act. It lives in wet places, sand dunes, waste land, and hedges.

Common Forms and Preparations

Hound's tongue (Cynoglossum officinale) is a plant. The leaf and root are sometimes used to make medicine. Hound's tongue has a long history of use as a medicinal herb, though it is rarely used in modern herbalism. The leaves contain allantoin, a highly effective agent that speeds up the healing process in the body. Historically, the plant has been prepared in several forms. It has been used in various forms, such as herbal teas, tinctures, and topical preparations, to address a wide range of health concerns, including inflammation, pain, and respiratory issues. The leaves and roots are described historically as analgesic, antihaemorrhoidal, antispasmodic, astringent, digestive, emollient, and slightly narcotic.

2. Traditional and Historical Use

European Herbal Tradition

The history of Cynoglossum officinale as a medicinal plant can be traced back to ancient times. Indigenous peoples across various regions recognized its healing properties and incorporated it into their traditional remedies. In Europe, it has a long history of use in traditional herbal medicine. It was often employed to treat respiratory ailments, such as coughs and bronchitis, due to its soothing properties.

Historical texts and herbals from the Middle Ages and Renaissance period documented the use of Cynoglossum officinale for various ailments, emphasizing its significance in traditional medicine. In the 19th century, it found its place in eclectic medicine, a form of American herbalism, where it was used as a remedy for respiratory issues, skin conditions, and pain relief.

According to King's American Dispensatory (1898), written by Felter and Lloyd — the primary reference text of American eclectic medicine — the herb was described as anodyne, demulcent, and astringent, and had been used in coughs, catarrhs, hemoptysis, diarrhoea, and dysentery. Externally, in the form of a poultice, it had been found highly beneficial in scrofulous tumors, burns, and goitre, and could be applied to recent contusions or inflammations with much advantage. The Dispensatory further noted that C. officinale "has been used as a demulcent and sedative in coughs, catarrh, spitting of blood, dysentery, and diarrhea, and has been also applied externally in burns, ulcers, scrofulous tumors and goiter."

The roots have been used for their astringent and healing properties and for their sedative, calming, and slightly narcotic effects. This species, originating from Europe where it grows wild in mountainous fields, has been cultivated specifically for its medicinal properties.

Native American Traditional Use

Native American tribes, including the Cherokee, utilized Cynoglossum officinale for its analgesic effects. It was applied topically to alleviate pain from injuries and wounds. A related North American species, Cynoglossum morrisoni (Beggar's-lice), was used by the Cherokee: a decoction of root or top was drunk for kidney troubles; bruised root was used with bear oil as an ointment for cancer; and forgetful persons drank a decoction from an idea that the sticking qualities of the burs would be imparted to the memory. The root was also used in the preparation of love charms.

Modern Eclectic and External Use

In contemporary botanical medicine, hound's tongue is regarded as a topically applied vulnerary, essentially identical in use to Comfrey. Due to its allantoin concentration, it is best used as a mender of wounds, ulcerations, and cuts, and it has been said to excel as a burn dressing and healer of residual tissue disruption from bites, stings, and outbreaks. Herbalists have used the plant as a treatment for piles, lung diseases, and persistent coughs. Houndstongue ointment has also been said to treat baldness and used for sores and ulcers.

The plant has been used internally in the treatment of coughs and diarrhoea, though it is now mainly used externally as a poultice on piles, wounds, minor injuries, bites, and ulcers.

3. Key Constituents and Active Compounds

Pyrrolizidine Alkaloids (PAs): Primary Profile

Cynoglossum officinale (Boraginaceae) contains high levels of pyrrolizidine alkaloids. It was the first plant species known to be able to synthesize PAs in both shoots and roots. The facultative biennial Cynoglossum officinale contains the N-oxides of the following pyrrolizidine alkaloids (PAs): trachelanthamine, viridiflorine, 7-angeloylheliotridine, rinderine, echinatine, 3′-acetylechinatine, and heliosupine.

Heliosupine, heliosupine N-oxide, 3′-acetylheliosupine, and viridiflorine have been isolated and identified by MS, ¹H and ¹³C NMR from Cynoglossum officinale. Altogether, 14 pyrrolizidine alkaloids were separated and identified by GLC and GLC-MS in the alkaloid extracts from different parts of Cynoglossum officinale.

Phytochemical analysis has revealed the presence of heliosupine, 3′-acetylheliosupine, echinatine, 7-angeloylheliotridine, and 12-acetylheliosupine as the main PAs in the genus Cynoglossum. Hound's-tongue was found to contain large quantities — 0.6% to 2.1% on a dry matter basis — of toxic pyrrolizidine alkaloids.

The Alkaloid Cynoglossine

An alkaloid, cynoglossine, was found to exist in the alcoholic extracts of the roots and seeds of the plant, but not in the stems or the leaves. The authors who initially characterized it could not establish any curarine-like physiological properties, as had been claimed by others. The plant contains the alkaloids cynoglossine and consolidin, which have been used medicinally to relieve pain. They depress the central nervous system and are also potentially carcinogenic.

Allantoin

The leaves contain allantoin, a highly effective agent that speeds up the healing process in the body. Allantoin is a well-characterized cell proliferant. Allantoin is a potent cell-proliferator which stimulates the growth of healthy tissue, speeds wound-healing, and reduces scar-formation. Due to its allantoin concentration, hound's tongue is best regarded as a mender of wounds, ulcerations, and cuts.

Mucilage Polysaccharides and Other Secondary Metabolites

Most hepatotoxic PAs are esters of two amino alcohols, retronecine and heliotridine, and occur in three groups — monoesters, noncyclic (open) diesters, and cyclic diesters — in ascending order of toxicity. PAs require a 1,2 double bond in the pyrrolizidine nucleus (necine) and a branch in the ester group to be hepatotoxic. Nontoxic N-oxides of PAs may be converted to the toxic free base in the alimentary tract.

Pyrrolizidine alkaloids are among the most common secondary metabolites isolated from Boraginaceae species. The nitrogenous necine moiety of PAs originates from L-ornithine or L-arginine, with putrescine and homospermidine as biosynthetic intermediates, while necic acids originate biosynthetically from the amino acids L-valine, L-leucine, L-isoleucine, and L-threonine.

Beyond the PA alkaloid fraction, additional secondary metabolites have been characterized in members of the Cynoglossum genus. A total of 47 chemical components, including alkaloids (pyrrolizidine alkaloids), sterols, organic acids, and saccharides, have been isolated from C. amabile, a closely related species. Within Cynoglossum species generally, rosmarinic acid has been identified: echinatine N-oxide, rosmarinic acid, and 9″-methyl lithospermate have been isolated from root extracts.

4. Mechanisms of Action

Hepatotoxic Mechanism of Pyrrolizidine Alkaloids

After ingestion, PAs undergo hepatic cytochrome P450 (CYP)-mediated metabolic activation to generate dehydropyrrolizidine alkaloids (DHPAs), which are hydrolyzed to dehydroretronecine (DHR). Reactive metabolites (DHPA and DHR) of PA, but not the intact PA itself, exert hepatotoxicity. Hepatic sinusoidal endothelial cells (HSECs) are more susceptible to these reactive metabolites compared with hepatocytes. The susceptibility of HSECs correlates with glutathione depletion and pyrrole-protein adduction.

Acute and subacute PA poisoning can lead to severe liver damage in humans and animals, comprising liver pain, hepatomegaly, and the development of ascites due to occlusion of the hepatic sinusoids (veno-occlusive disease). Chronic exposure to low levels of PA can induce liver cirrhosis and liver cancer.

Prolonged exposures may cause cell enlargement (megalocytosis), veno-occlusion in liver and lungs, fatty degeneration, nuclei enlargement with increasing nuclear chromatin, loss of metabolic function, inhibition of mitosis, proliferation of biliary tract epithelium, liver cirrhosis, nodular hyperplasia, and adenomas or carcinomas.

PA Toxicity Type in Hound's Tongue

The pyrrolizidine base present in Cynoglossum officinale (heliotridine) and its esters have a similar type of toxicity to the highly toxic and more familiar macrocyclic diester pyrrolizidine alkaloids of the pyrrolizidine base (retronecine), present in Senecio or Crotalaria species.

Allantoin: Wound-Healing Mechanism

Allantoin and rosmarinic acid are chiefly responsible for the pharmacodynamic effects attributed to vulnerary Boraginaceae preparations. Allantoin is a potent cell-proliferator which stimulates the growth of healthy tissue, speeds wound-healing, and reduces scar-formation. The mucilaginous polysaccharides also have a local anti-inflammatory and soothing action.

5. Scientific Evidence by Area of Use

5.1 Wound Healing and Topical Applications

The most credible pharmacological basis for hound's tongue's traditional topical use lies in its allantoin content. The leaves contain allantoin, a highly effective agent that speeds up the healing process in the body. Allantoin has been independently studied, primarily in Comfrey (Symphytum officinale), a plant from the same Boraginaceae family with comparable allantoin levels. This makes Boraginaceous plants containing allantoin ideal for topical applications to the skin for bruises, swellings, irritable skin lesions, wounds, ulcers, insect bites, eczema, and psoriasis.

Evidence strength: There are no published controlled clinical trials specifically investigating topical Cynoglossum officinale preparations in human subjects for wound healing. The rationale for topical use is extrapolated from the known pharmacology of allantoin as an isolated compound and from studies of the related Comfrey plant; there is no direct clinical evidence unique to hound's tongue.

5.2 Respiratory Conditions (Cough, Bronchitis, Catarrhea)

Per the eclectic tradition, the plant was described as anodyne, demulcent, and astringent, and had been used in coughs, catarrhs, hemoptysis, diarrhoea, and dysentery. In Europe, Cynoglossum officinale has a long history of use in traditional herbal medicine. It was often employed to treat respiratory ailments, such as coughs and bronchitis, due to its soothing properties.

Evidence strength: There are no published clinical trials examining the effect of hound's tongue preparations on respiratory conditions in human subjects. The respiratory use is based entirely on historical ethnobotanical observation. People use hound's tongue for infections, wound healing, and many other purposes, but there is no good scientific evidence to support any use.

5.3 Gastrointestinal Conditions (Diarrhoea, Dysentery)

The plant has been documented as a demulcent and sedative in coughs, catarrh, spitting of blood, dysentery, and diarrhea. The astringent activity attributed to tannins in the leaves and roots may provide a pharmacological basis for traditional antidiarrhoeal use, as tannins are known to reduce intestinal secretion and to exert antimicrobial effects.

Evidence strength: Entirely traditional and observational. No clinical or preclinical studies specifically addressing C. officinale for gastrointestinal conditions have been identified in the literature.

5.4 Pain Relief and Sedation (Analgesic/Narcotic Effects)

The plant contains the alkaloids cynoglossine and consolidin, which have been used medicinally to relieve pain. They depress the central nervous system and are also potentially carcinogenic. Native American tribes, including the Cherokee, utilized Cynoglossum officinale for its analgesic effects. It was applied topically to alleviate pain from injuries and wounds.

Evidence strength: Alkaloids in the plant have historically been attributed with analgesic and mild narcotic effects. However, researchers have not been able to establish curarine-like physiological properties for cynoglossine, as claimed by earlier investigators. There are no controlled human trials. The analgesic claim is based on traditional use and historical pharmacological characterization.

5.5 Research on the Related Species Cynoglossum amabile

A body of phytochemical and pharmacological research has been conducted on Cynoglossum amabile (Chinese hound's tongue), a closely related species. While distinct from C. officinale, this research offers relevant context, as the two species share many alkaloid constituents. Pharmacological studies show that the chemical extracts of C. amabile possess various biological activities, such as anti-inflammatory, anti-tumor, anti-microbial, cardiovascular effects, ganglionic action, and acetylcholinesterase inhibition. Although preliminary studies suggest potential applications in the treatment of prostate diseases and alopecia, further research is needed to validate these clinical uses.

C. amabile has been traditionally used for medicinal, edible, and ornamental purposes in China for many centuries. The whole plant, root, and leaf are used by different ethnic groups, such as Lisu, Bai, Naxi, Yi, Jinuo, and Han, to treat malaria, hepatitis, dysentery, leucorrhea, tuberculosis cough, fracture, joint dislocation, trauma bleeding, and skin carbuncle abscess.

Evidence strength: Preliminary, largely in vitro and animal-model studies on a related species. None of this research constitutes clinical evidence applicable to C. officinale specifically, and none is sufficient to justify medicinal use given the documented toxicity profile.

6. Body Systems and Health Areas Associated with Hound's Tongue

Integumentary system (skin): Topical use for wounds, burns, ulcers, bruises, sores, piles, bites, and stings — based on allantoin and mucilage content.
Respiratory system: Traditional use for coughs, catarrh, bronchitis, and hemoptysis — demulcent properties attributed to mucilage.
Gastrointestinal system: Traditional use for diarrhoea, dysentery, and digestive complaints — astringent and demulcent properties.
Nervous system: Historical use as a mild analgesic and sedative — attributed to cynoglossine and consolidin alkaloids.
Hepatic system: A primary concern, as the plant's PA content poses documented hepatotoxic risk rather than benefit.

7. Dosage Forms and Reported Dosages

The leaves and roots are described as analgesic, antihaemorrhoidal, antispasmodic, astringent, digestive, emollient, and slightly narcotic. Historically, both internal and external preparations were described:

Poultice (external): Described as anodyne, demulcent, and astringent for internal use in coughs, catarrhs, hemoptysis, diarrhoea, and dysentery; and externally, in the form of a poultice, it was found highly beneficial in scrofulous tumors, burns, and goitre, and applied to contusions or inflammations with advantage.
Tinctures and herbal teas: The plant has been used in forms such as herbal teas and tinctures, though no specific dosages have been established in clinical studies.

No controlled clinical trials have been published establishing safe or effective dosage ranges for Cynoglossum officinale in human subjects. Given the regulatory position described below, no endorsed therapeutic dosage exists for internal use.

8. Safety Considerations and Regulatory Status

Pyrrolizidine Alkaloid Toxicity: Human and Animal Evidence

Cynoglossum officinale (hound's tongue) contains alkaloids with curare-like activity as well as hepatotoxic and carcinogenic pyrrolizidine alkaloids. The plant contains chemicals called pyrrolizidine alkaloids (PAs). These chemicals can be toxic to the lungs and the liver.

Animal studies have produced direct and well-documented evidence of severe hepatotoxicity. The death of 10 horses was attributed to feeding dried grass hay containing hound's-tongue, Cynoglossum officinale. Affected horses developed weight loss, icterus, photosensitization, and hepatic encephalopathy. Histologic examination of the liver of 3 of the horses revealed megalocytosis, biliary hyperplasia, and fibrosis characteristic of pyrrolizidine alkaloid poisoning. In an experimental study, six calves were given dried, ground Cynoglossum officinale daily in a dose that provided 15 or 60 mg per kg per day of total pyrrolizidine alkaloids. Those calves given 60 mg per kg of total pyrrolizidine alkaloids per day died following a single dose of plant material. These calves had a marked elevation of serum gamma-glutamyltransferase (GGT) and aspartate transaminase (AST) activities and serum bile acid and total bilirubin concentrations. All four calves at the higher dose had massive hepatocellular necrosis and haemorrhage of the liver.

Human Hepatotoxicity and Veno-Occlusive Disease

PAs and their N-oxides are toxic to both humans and livestock through consumption of PA-containing plants or food contaminated with PAs such as meat, milk, and honey. Exposure to PAs has been regarded as one of the two major causes of hepatic sinusoidal obstruction syndrome (HSOS, previously called hepatic veno-occlusive disease), which is a rare hepatic vascular disease with a high mortality rate. The earliest case of PAs-induced HSOS was reported in 1920. Since then, more than 8,000 pyrrolizidine alkaloid poisoning cases have been documented in many countries, including Afghanistan, Britain, China, Germany, Hong Kong, India, Jamaica, South Africa, Switzerland, and the United States.

In humans, chronic exposure causes veno-occlusive disease (VOD) of the liver. The pathogenesis of VOD remains poorly understood; studies suggest that endothelial cell injury, cytokines, and haemostatic derangement are all involved in its pathogenesis.

Genotoxicity and Carcinogenicity

PAs have been reported to be hepatotoxic, mutagenic, and carcinogenic; they are a significant group of natural toxins affecting livestock, wildlife, and humans. Pyrrolizidine alkaloids can cause liver damage and show genotoxic and carcinogenic effects in animal experiments, with no safe threshold value being derived.

Dermal Risks

Contact with the plant can cause dermatitis in sensitive people. Hound's tongue contains a number of hepatotoxic pyrrolizidine alkaloids, often in concentrations higher than Russian comfrey.

Regulatory Status

The use of the plant or any of its extracts is not considered safe because of the high alkaloidal content. Therefore, the German Federal Health Bureau (1992) does not approve any therapeutic application of the plant.

As a regulatory measure aimed at protecting patients and consumers from the intake of toxic PA through medicinal products, some health authorities set strict limits for the PA content in medicinal products during the 1990s. The German health authority initiated a "graduated plan" in 1992 stating that the maximum daily exposure to PAs by medicinal products should not exceed 0.1 μg for internal use and 10 μg for external use. If the duration of application is limited to a maximum of 6 weeks per year, doses of up to 1 μg for internal and 100 μg for external use are accepted. Such higher doses are contraindicated for pregnant and breastfeeding women and, in the case of topical use, should only be applied on intact skin.

Because of the toxic effects of PAs, the German Federal Institute of Risk Assessment (BfR) established more stringent limits in 2011, whereby a daily intake of less than 0.007 µg/kg body weight was recommended. The Herbal Medicinal Products Committee (HMPC) of the EMA published an updated public statement on pyrrolizidine alkaloids. The statement contains, among other things, the limit values for the daily maximum intake of PAs. The earlier 2014 document contained 0.35 µg PAs per day as a maximum intake level.

The German Federal Health Office has restricted the availability of botanical medicines containing unsaturated pyrrolizidine alkaloids. When taken by mouth, hound's tongue is regarded as likely unsafe.

Interactions and Special Populations

Nontoxic N-oxides of PAs may be converted to the toxic free base in the alimentary tract. This conversion is relevant for oral ingestion scenarios and indicates that even preparations with predominantly N-oxide forms are not inherently safe for internal consumption. Acute toxicity will depend on the amount of PA ingested and on the metabolism of each person, since the conjugation of glutathione with the reactive metabolites generated can be an important detoxification pathway in the body. Drugs or conditions that deplete hepatic glutathione or induce CYP enzymes — including alcohol use and concurrent hepatotoxic medications — may increase the risk of PA-related liver injury. Higher doses are specifically contraindicated for pregnant and breastfeeding women.

9. Summary of Evidence Status

Hound's tongue (Cynoglossum officinale) has a documented history of use in European, North American eclectic, and indigenous medical traditions spanning centuries, primarily for respiratory complaints, gastrointestinal disorders, and topical wound care. The pharmacological rationale for topical use rests primarily on allantoin and mucilaginous polysaccharide content. However, there is no good scientific evidence from controlled clinical trials to support any therapeutic use of hound's tongue in humans. Simultaneously, the plant carries a well-documented, peer-reviewed toxicological profile centered on its high content of 1,2-unsaturated pyrrolizidine alkaloids — compounds with established hepatotoxic, mutagenic, and carcinogenic properties in both animals and humans. Because of this high alkaloidal content, the German Federal Health Bureau (1992) does not approve any therapeutic application of the plant. The current scientific and regulatory consensus strongly discourages internal use, and modern botanical medicine practice has largely restricted any consideration of the plant to externally applied preparations on intact skin, where PA absorption is lower.

References

Health Conditions

Health conditions that Hound's tongue may help support.

No conditions available.

Body Systems

Body systems that Hound's tongue may help support.

No body systems available.