Comfrey

Botanical Name: Symphytum officinale, Boraginaceae

Common names: Comfrey, Knitbone, Knitback, Consound, Blackwort, Bruisewort, Slippery Root, Boneset, Gum Plant, Ass Ear.

Plant description: Comfrey is a herbaceous perennial, arising from a long fleshy mucilaginous root with a black epidermis and white cortex, appearing in spring as a basal rosette of bright green leaves. When mature the erect stem attains a height of between 90 and 120 cm, branching above, the lower leaves ovate-lanceolate, the upper leaves more lanceolate. All aerial portions except the flowers are noted for their stiff white hairs that give the plant a rough texture. The white, purple or pink flowers are borne in terminal, one-sided racemes. The calyx is comprised of five parts, with lanceolate acuminate sepals, the corolla tubular to campanulate, stamens 5 and style filiform. The flowers give way to small smooth ovate seeds.

Habitat, ecology and distribution: Comfrey is native to Europe, and is now widespread in temperate regions of North America, occurring along roadsides, in fields pastures and gardens, often preferring a deep, rich soil. It is typically absent from drier areas.

Part used: Root, leaf.

History: The name ‘Comfrey’ derived from the latin term con firma (‘with form’), an allusion to Comfrey’s ability to unite broken bones, and similarly, the genus name ‘Symphytum,’ is derived from the Greek symphyo, meaning ‘to unite.’ Although it is a practice somewhat in dispute now, Comfrey has a long history as a food plant, the young leaves used as a substitute for Spinach, and the young shoots as a pot herb after blanching. Grieve mentions that strong decoction has been used in the past for tanning leather, and that in Angora a kind of glue is obtained from Comfrey, traditionally used in spinning wool.

Constituents: Comfrey is notable, or perhaps notorious, for its alkaloidal content, primarily of the pyrrolizidine type, containing upwards of 3%, including symphytine, symlandine, echimidine, intermidine, lycopsamine, myoscorpine, acetyllycopsamine, acetyleintermidine, lasiocarpine, heliosupine, viridiflorine, and echiumine. Rode reports that nearly all (85–97%) of the PAs in the common Comfrey are retronecine monoesters or are readily hydrolyzed to monoesters (2002). In contrast, the Russian Comfrey (Symphytum x uplanidicum) contains a high proportion of the slightly more toxic retronecine diester form of pyrrolizidine alkaloids (PAs). In regard to its traditional use however, the more important class of constituents are the carbohydrates and mucilage, as well as allantoin, of which Comfrey contains upwards of 2.55%. Other constituents include steroidal saponins and triterpenes, including sitosterol, stigmasterol and isobauerenol, tannins, plant acids (caffeic, chlorogenic, lithospermic, rosmarinic and silicic acids), carotenoids, protein (35%, including sulfur-containing amino acids), and vitamin B12 (Newall et al 1996, 87; Duke 2003; Rode 2002).

Medical Research: Due to the recent concern over the potential hepatotoxicity of Comfrey, there has been little interest in verifying its benefit in human clinical trials, despite a long and important history of usage. In regards to its topical usage, one recent open, uncontrolled clinical trial examined the efficacy of a Comfrey ointment in 105 patients with locomotor system symptoms. Researchers noted a clear therapeutic effect in chronic and subacute symptoms, most effective against muscle pain, swelling, arthritis and vertebral syndrome (Kucera et al 2000). Goldman et al report a vulnerary and analgesic effect in experimental animals when Comfrey was administered orally (1985). Mills reports that much of the effects of Comfrey are due to the presence of allantoin, which promotes fibroblast, chondroblast and osteoblast activity, resulting in connective tissue remodeling (1991, 545). According to Mills, allantoin is readily absorbed into the tissues when applied topically as a fresh plant poultice, a process facilitated by the plastering effect of Comfrey’s mucilages, tannins and resins as they dry (1991, 545). In the gut, an aqueous extract of Comfrey enhances the release of prostaglandin F series that protect the gastric wall from damage (1991, 545).

Toxicity: Comfrey is generally regarded as being toxic due to the presence of pyrrolizidine alkaloids. In the 1990’s there were a series of reported cases of veno-occlusive disease (VOD) associated with Comfrey ingestion, usually in association with other factors such as illness, poor nutritional status and the concurrent use of hepatotoxic drugs (e.g. acetaminophen) (Rode 2002). To determine the safety of Comfrey a series of studies have been conducted to examine the potential toxicity of Comfrey and other PA-containing plants such as Senecio jacobaea in experimental animal models. Rode reports that the inherent toxicity of PAs varies to a large degree depending on the animal model used, providing data that pigs, chickens and rats are highly sensitive to PA poisoning, whereas mice and sheep are resistant (2002). In some of these studies, the toxic potential of PAs was determined by administrative routes other than oral, such as by injection, and this too has been shown to have an enormous impact on the potential toxicity of PA-containing herbs (Rode 2002). Rats in particular appear to be very sensitive to PAs, developing liver tumors and hepatic lesions with both the oral and injected administration of Comfrey, but may not be an appropriate model to base potential human toxicity upon because humans appear to metabolize PAs differently (Rode 2002). In many cases, toxicity studies have been conducted on the isolated PAs, which cannot be equated with the whole plant extract. Rode reports that the formation of PA toxic metabolites is attenuated by the concurrent administration of sulfur-containing amino acids such as methionine or cysteine, and that toxicity is enhanced by a low protein diet (Rode 2002). In regard to the potential toxic effects of Comfrey in humans, one small study of 29 long term users found that the typical markers for liver disease, including elevated aspartate aminotransferase (AST) G-glutamyltransferase (GGT), bilirubin and a-fetoprotein (AFP), were normal even after prolonged consumption of the leaf (Anderson and McLean 1989). Currently, the distribution of Comfrey is restricted in Canada, its use in Germany is limited to external application, and in the USA, the Food and Drug Administration has requested voluntary compliance for the removal of products containing Comfrey. In the UK, the Medicine Control Agency has recently included comfrey in a list of herbs under consideration for restriction to medical prescription only (Rode 2002).

Herbal action: vulnerary, antihemorrhagic, demulcent, relaxing expectorant, astringent

Indications: cuts, abrasions, wounds, broken bones, torn cartilage, ligaments and tendons, gastric and duodenal ulcers, bronchitis, tuberculosis

Contraindications and cautions: In view of the concerns regarding Comfrey, it should not be used continuously for more a two week period. The internal use of Comfrey should be avoided in vegetarians, in those who are chronically ill, have liver disease or are taking potentially hepatotoxic drugs, and during pregnancy and lactation. For infected wounds Comfrey should not be used until one is certain that the infection has been dealt with, to avoid causing an abscess.

Medicinal uses: Comfrey is the most valued and powerful vulnerary in the materia medica, used both internally and topically for a variety of injuries, inflammations or ulcerations. Wherever Comfrey has grown the native tongue has almost always named Comfrey as some kind of ‘knit-bone,’ so important and universal its reputation as a vulnerary. Although some may attribute Comfrey’s healing power to allantoin alone, the other mucilaginous and astringent constituents greatly facilitate this vulnerary effect, helping to draw the edges of the wound together. To treat external injuries Comfrey is best applied as fresh plant poultice. This can be done chopping the root in small chunks, and then further dessicating the root in a food processor. The sloppy mucilaginous mixture can then applied on the wound and covered with bandage. Similarly, a strong decoction can be made and then used as a fomentation. Felter and Lloyd report that Comfrey root is useful in “…diarrhoea, dysentery, bronchial irritation, coughs, hemoptysis, other pulmonary affections, leucorrhoea, and female debility” (1893). In the treatment of gastrointestinal ulceration Comfrey is of great benefit to inhibit further damage and heal the inflammed lesions, drunk as an infusion of the dried leaf for a few days up to a week.

Pharmacy and dosage:

• Fresh Plant Tincture: fresh root and leaf, 1:2, 95% alcohol, 20-60 gtt, 1-4 mL
• Dry Plant Tincture: recently dried root and leaf, 40% alcohol, 20-60 gtt, 1-4 mL
• Hot Infusion: recently dried leaf, 1:20, 60-120 mL
• Powder: recently dried leaf, 500-2000 mg