Comfrey, Symphytum officinale, is in the Boraginaceae family along with bluebells and forget-me-nots. This plant originated in Europe and temperate climates in Asia; it has been cultivated as a healer for almost 2500 years. Comfrey is also known as knitbone, blackwort, bruisewort, gum plant, healing herb, salsify and slippery root. The parts used are the root and rhizome and the leaf. Comfrey's properties are vulnerary, demulcent, anti-inflammatory, astringent and expectorant. Traditionally, comfrey has been used to ease inflammation from sprains and broken bones and also to treat wounds. It continues to be used this way today by modern herbalists.
Comfrey is an extremely mucilaginous plant, even more so than marshmallow. This mucilage can be wrapped around a broken bone or applied as a poultice. When treating wounds, it's important to combine comfrey with an antiseptic herb such as Echinacea purpurea, goldenseal or calendula. Comfrey's high protein content may make open wounds a breeding ground for bacteria even as it speeds their healing. Cuts and abrasions should also be as clean as possible before applying comfrey, due to comfrey's admirably fast rate of healing.
Comfrey acts as a vulnerary by reducing inflammation at fracture sites, easing the passage for bones to knit together. Traditionally, comfrey has also been used internally for ulcers, diarrhea and respiratory illnesses such as pleurisy and bronchitis. It has also been used in place of marshmallow to act similarly on intestinal problems. Native peoples have used comfrey to treat abscesses, enlarged glands, hernias and amenorrhea.
The issue of applying comfrey to broken skin is a confusing one. Many sources state strongly that comfrey should never be applied to broken skin, while other sources explain that it is upon broken skin that comfrey displays its most admirable qualities. For personal use, I often apply comfrey to broken skin. It's become my go-to resource for this purpose. I always pair comfrey with an antiseptic herb, as mentioned above, and I suspect that the reason many conventional resources discourage its use in this way is because, as I mentioned, its protein content and power as a speedy healer could encourage infection if the proper precautions are not taken. I believe that if one is cautious about properly cleaning wounds and applying antiseptics in conjunction with comfrey, it's a worthwhile practice to use comfrey with wounds of all types. I've had several excellent successes with this plant. It is important to treat this powerful herb with respect and to avoid using it with abandon. It requires a careful hand and a suspicious nature regarding infection. But I would recommend this herb without hesitation to those willing to approach it with reverence.
Researchers believe that it is the presence of allantoin that lends comfrey its usefulness in the healing of wounds and fractures. This chemical, also found in breastmilk, encourages cell growth, which aids healing inside and out. Allantoin increases the production of white blood cells and encourages cell proliferation, while possessing anti-irritant and moisturizing properties.
As mentioned above, comfrey has traditionally been used as an internal treatment. This practice has recently fallen out of favor with the discovery that comfrey-pepsin capsules, which are marketed as a digestive aid, contain pyrrolizidine alkaloids. Ingestion of these capsules has been linked to cases of hepatic veno-occlusive disease. Pyrrolizidine alkaloids may also be carcinogenic, especially to the liver. Though no liver toxicity has been detected in groups of humans who regularly consume comfrey, animal studies [PDF file] have indicated that pyrrolizidine alkaloids cause hepatomas and other liver pathologies. For these reasons, comfrey has been banned or restricted in some countries such as Canada, Australia and Brazil. The FDA has strongly discouraged the use of comfrey in the US, though it has not yet attempted to restrict it.
In analyzing the data from the above-mentioned animal studies, two issues become immediately clear. The first is that the rats were fed a quantity of comfrey that would translate unrealistically to human intake. In some studies, comfrey leaves composed 30% of the rats' diet for a period of 480-600 days, while comfrey roots were fed to the rats for 245-280 days. In other studies, the milled, extracted and purified version of the pyrrolizidine alkaloid, symphytine, was also injected into the rats for almost two months. These dosages are not indicative of the standard usage for a healthy adult human. It's unsurprising, considering the very small caloric value of any sort of green leafy plant, that a 30% comfrey diet resulted in reduced weight gain for the rats.
Another issue is the use of the fresh plant compared to ready-to-use, or even extracted, preparations. Many of the animal studies involving comfrey utilized an extracted compound of pyrrolizidine alkaloid. While these studies did demonstrate the hepatotoxic quality of these alkaloids, it would be irresponsible to consider these studies the final word on the toxic or carcinogenic quality of the whole plant. Edible and medicinal plants contain thousands of different compounds and chemicals, many of which have yet to be identified, labeled or studied. It has been demonstrated in studies such as the Beta Carotene Chemoprevention Trial (CARET) and the Alpha-Tocopherol, Beta Carotene Cancer Prevention Trial (ATBC) that applying an extracted chemical rather than encouraging the ingestion of the whole plant results in very different effects. The CARET study, which examined the effects of extracted beta carotene rather than the ingestion of plants that contained carotenoids, was halted before completion due to the apparent result that beta carotene encouraged cancer in smokers rather than preventing it. It's been definitively proven, however, that consuming plants that contain carotenoids such as beta carotene helps to prevent cancer in a wide variety of subjects.
In the case of human disease in which comfrey is implicated, a major issue seems to be with the ingestion of the aforementioned comfrey-pepsin tablets, which are administered for digestive problems. The abstract of one study mentions a New Zealand newspaper article about a young man who died from liver collapse after regular consumption of comfrey. No other information is given about this “case study.” Another case involved an older woman who consumed 10 cups of comfrey tea and handfuls of comfrey pills a day for over a year. One case involved a man who experienced light-headedness, confusion, dilated pupils, rapid heartbeat and difficulty urinating after consuming comfrey that was most likely contaminated with atropine, an alkaloid extracted from plants such as deadly nightshade. One 77-year-old woman experienced liver and pulmonary disease after consuming a combination of comfrey and scullcap for six months. Other cases mentioned in this study only indicated that the individual in question had consumed “large amounts” of comfrey without information regarding the quantity, the duration, the preparation or what part of the plant was being used. It is questionable, again, whether these case studies exemplify a standardized experience.
There are reasons to be concerned about comfrey's pyrrolizidine alkaloid content. The effects of these alkaloids may be cumulative, despite evidence that they are excreted in animals within 24 hours. For this reason, it may be difficult to track liver disease or some other dysfunction to the use of comfrey. In cases that have been definitively linked to the use of comfrey, the patient in question was usually consuming massive quantities of the plant. Without the questionable benefit of such an obviously extreme intake, it can be difficult to understand the exact result of consistent, or even occasional, low-dose intake of comfrey.
The use of comfrey in packaged herbal remedies is questionable. There is no standardization for the sale of comfrey. There is often no information provided regarding whether the root or the leaf is used in the product, despite the fact that their properties and effects can be very different. Pyrrolizidine alkaloid content can vary widely from one product to the next. Comfrey's contents may depend on when and where the plant is harvested and how it is prepared and applied. Individuals should perhaps steer clear of prepared comfrey products and instead grow their own comfrey or harvest it from a reputable, consistent site. It would also be advised that those with liver disease avoid ingesting the plant. Children and the elderly should perhaps avoid ingesting comfrey until more is known about its effect on developing or weakened constitutions. The use of comfrey should perhaps be confined to use of the plant in a minimally-processed form, as a mild tea or topical application, rather than extracts, tinctures or capsules.
As in all things, moderation is the key. Plants are powerful and they should not be used indiscriminately. There is no doubt that comfrey provides impressive benefits as a topical application for wounds, fractures and inflammation. A caution might be warranted to confine the use of comfrey for external healing with only limited, short-term application for internal use.
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