Known interactions

Agueweed, American Scullcap, Arberry, Arctostaphylos uva-ursi, Awa, Baldarian, Bear Grape, Bearberry, Bee Bread, Blue Pimpernel, Boneset, Borage, Borago officinalis, Bugloss, Chaparral, Common Borage, Common Bugloss, Common Scullcap, Coralillo, Creosote bush, Crosswort, Eupatorium, Eupatorium perfoliatum, Feverwort, Garden Heliotrope, Gravelroot, Greaswood, Hediondilla, Helmet Flower, Hogberry, Hoodwort, Indian Sage, Kava, Kava-Kava, Kawa, Kew, Kinnikinnick, Larrea divaricata, Larrea glutinosa, Larrea tridentata, Mad-Dog Weed, Mealberry, Mountain Cranberry, Ox's Tongue, Pennyroyal, Piper methysticum, Quaker Bonnet, Rockberry, Sandberry, Scullcap, Scutellaria lateriflora, Skullcap, Starflower, Stinkweed, Sweating Plant, Teasel, Thoroughwort, Tonga, Uva Ursi, Valerian, Valeriana officinalis, Valeriana sambucifolia, Valeriana wallichi, Valeriane, Yagona.

On-line Wallwort

Scientific Name: Comfrey

Other Names: Ass Ear, Black Root, Blackwort, Bruisewort, Common Comfrey, Consolidae Radix, Consound, Gum Plant, Healing Herb, Knitback, Knitbone, Salsify, Slippery Root, Symphytum Radix, Symphytum officinale, Wallwort

Who is this for?

Comfrey contains chemicals that make it unsafe to take by mouth. Known as pyrrolizidine alkaloids, some of these chemicals have been associated with liver damage in humans. Some study animals that were given comfrey developed liver cancer.

In 2001, the U.S. Food and Drug Administration (FDA) and the U.S. Federal Trade Commission (FTC) asked manufacturers to remove all oral comfrey products from the U.S. market. Oral forms of comfrey are also prohibited in several other countries, but they may be sold in some places if they are labeled as a dietary supplement. Warnings were also placed on the labels of topical products that contain comfrey. As recently as December 2003, the Canadian health organization, Health Canada, re-issued warnings that comfrey products may contain harmful chemicals and that comfrey should neither be taken orally nor be applied to raw skin.

Not all pyrrolizidine alkaloids are poisonous to humans, but the kinds, amounts, and proportions of pyrrolizidine alkaloids in comfrey products may vary greatly. Which type of comfrey plants were used, where they grew, what the weather conditions were, what time of year they were harvested, how they are processed, and where they were stored, all may affect the composition of commercial comfrey products. Similar products from different manufacturers and even different batches of the same product may have very different contents.

In addition, individual response to pyrrolizidine alkaloids is also quite variable. Some individuals, particularly children, senior adults, poorly nourished individuals, and those who have chronic illnesses, may have adverse results from doses of comfrey that are not toxic to other individuals. In a few documented case reports; however, young and middle-aged adults with no apparent health conditions are believed to have suffered liver damage from taking comfrey. The damage may be gradual, so comfrey poisoning may not be evident for periods up to 3 months.

Especially when high doses are used, or when low doses have been taken for long periods of time, pyrrolizidine alkaloids have been associated with causing a rare, but severe condition known as hepatic veno-occlusive disease. In this condition, the blood veins in the liver become clogged because a liver enzyme changes pyrrolizidine alkaloids into chemicals that may stick to the inside of veins and damage vein tissue. They may also damage lung tissue, potentially resulting in pulmonary hypertension, which is high blood pressure in the artery from the heart to the lungs. Some of the chemicals produced when pyrrolizidine alkaloids break down may stay in the body for years, continuing to damage blood vessels or other tissue.

However, comfrey contains several potentially beneficial substances that may be applied to the skin. Generally, it has high concentrations of allantoin, a protein that encourages new cells to grow; rosmarinic acid, which is known to be anti-inflammatory; and tannins, that help to firm skin tone. Because comfrey also contains mucilage, which swells in liquids, it forms a soft, sticky covering that stays in contact with the skin. All of these properties make comfrey useful when applied topically to soothe and treat bruises, minor skin irritation, and sprains. Comfrey may also have slight pain-relieving properties. It should be used only on unbroken skin, however — not on large or open wounds. A mouth rinse made from comfrey may have some benefit in soothing sore gums and throat, but care must be taken not to swallow it. The mouth should be rinsed thoroughly with plain water after a comfrey rinse has been used.

When should I be careful taking it?

Comfrey should not be taken by mouth.

One case of damage to an unborn baby whose mother drank large amounts of comfrey tea during pregnancy has been reported, and birth defects are known to have occurred in laboratory animals born to mothers who were given comfrey during pregnancy. Comfrey may also have some muscle-tightening effects on the uterus. Therefore, taking it may have prompted miscarriages among laboratory animals. Additionally, potentially harmful chemicals from comfrey have been found in the milk of laboratory animals and livestock that ate it. No human studies verify that comfrey passes into human breast milk, but pregnant and breast-feeding women are advised to avoid taking comfrey by mouth.

After comfrey is applied to the skin, some of the chemicals in it may be absorbed into the body, but how much is absorbed cannot be determined in advance. Possibly, harmful amounts may accumulate, so pregnant women and women who are breast-feeding should also avoid applying topical comfrey.

Although no reliable reports of liver problems have been attributed to using comfrey on unbroken skin, individuals with liver problems and individuals who drink large amounts of alcohol should avoid its use on the skin.

Because children and the elderly may be affected by even small amounts of the pyrrolizidine alkaloids in comfrey, they should not use it in any form.


When it is used topically, comfrey should not be applied to large areas of skin or skin that is raw.

What side effects should I watch for?

When they are taken orally, the pyrrolizidine alkaloids in comfrey may be converted to toxic chemicals that have been shown to cause liver damage, primarily due to gradual blockage of blood vessels in the liver. In laboratory and farm animals, eating comfrey has resulted in liver cancer. Comfrey should never be taken by mouth.

Liver damage can take years to develop and it may not have obvious signs. Tell your doctor immediately if you are using comfrey and you experience:

  • Excessive fatigue
  • Extreme widespread itchiness
  • Nausea, vomiting or diarrhea
  • Pain or swelling in the upper right part of the abdomen
  • Yellowing of the skin or the white parts of the eyes

Less Severe Side Effects

People who have used topical comfrey for long periods of time or in high amounts have reported:

  • Abdominal pain
  • Loss of appetite
  • Unusual tiredness

Handling or coming in contact with the fuzzy leaves of the comfrey plant can cause skin irritation for some people.

What interactions should I watch for?

In laboratory studies, the drug phenobarbital may have caused comfrey to break down into toxic chemicals faster or more completely. Although no reports of an interaction between comfrey and phenobarbital have been reported in humans, one may be possible. Phenobarbital may be used to treat insomnia or to control seizures.

Several other herbal products, including borage, boneset, kava, pennyroyal oil, scullcap, uva ursi, and valerian, have been known to cause liver damage in humans. If comfrey is taken or applied at the same time as another herbal that may cause liver damage, the risk of liver damage could increase. Before using comfrey with other herbal products, check with your pharmacist to verify the ingredients.

Some interactions between herbal products and medications can be more severe than others. The best way for you to avoid harmful interactions is to tell your doctor and/or pharmacist what medications you are currently taking, including any over-the-counter products, vitamins, and herbals. For specific information on how comfrey interacts with drugs, other herbals, and foods and the severity of those interactions, please use our Drug Interactions Checker to check for possible interactions.

Should I take it?

Believed to have originated in Asia and Europe, comfrey now thrives in most temperate climates, At various times in history, it has been cultivated, but currently it most often grows wild in marshy areas or grassy meadows. A shrubby perennial plant that can reach 2 to 5 feet in height, it can be a nuisance – choking out crops and ornamental plants, if it is not controlled. Comfrey has thick, fuzzy stems, long lower leaves, and purple or blue bell-shaped flowers that bloom throughout the summer months. In some parts of the world, comfrey leaves were eaten as a vegetable, the roots were dried and roasted for a coffee substitute, and animal feed was made from the whole plant. In the summer of 2001, the FDA required the manufacturers of oral dietary supplements for humans to stop including comfrey. Since then, comfrey has also been removed from commercial animal feeds.

The leaves, rhizomes, and roots of comfrey have all been used in medicine. Rhizomes are fleshy extensions of plant stems that run along or under the ground and often produce shoots and roots for new plants. Until the 1960s when their pyrrolizidine alkaloid content was discovered, oral forms of comfrey were taken to treat digestive and respiratory conditions. More effective and safer oral products are now on the market. Although oral forms of comfrey still may be available in the United States and other countries, taking comfrey by mouth is not recommended due to rare but severe side effects potentially caused by pyrrolizidine alkaloids it contains. In general, the underground parts of comfrey (roots and rhizomes) contain much more of the pyrrolizidine alkaloids than the leaves; and the small, new leaves have more than larger, older leaves. Comfrey may be added to creams, gels, salves, or ointments to treat conditions such as acne and psoriasis, as long as the skin is intact and not raw. It is also included in soaps, cosmetics, dry skin lotions, and lip balms.

Dosage and Administration

Due to the possibility that it may cause liver damage, comfrey is not recommended for oral use.

Topical preparations that include comfrey, such as diaper creams or chapped-lip ointments, usually contain between 5% and 20% of an extract made from the leaves or roots of comfrey. The pyrrolizidine alkaloids that make comfrey unsuitable for oral use are also absorbed through the skin. How much is absorbed is not known. Therefore, only small amounts of comfrey-containing products should be applied per day for a maximum of 10 days at a time. The use of topical comfrey preparations should be limited to a total of 6 weeks or less per year.


Applied to unbroken skin, comfrey can help relieve inflammation and soreness caused by soft tissue injuries like bruises and by minor skin irritation. It should not be applied to deep cuts or for long periods of time and it should not be taken orally.


When taken by mouth, comfrey has been reported to cause liver damage — including liver cancer in animals and rare cases of veno-occlusive disease (obstructed blood vessels in the liver or lungs) in humans. While comfrey poisoning is extremely rare, it is also unpredictable. Comfrey should never be taken orally.

When comfrey products are applied to the skin, variable amounts of pyrrolizidine alkaloids may be absorbed into the body. Topical comfrey should be used in small amounts for a maximum of 10 days at a time for a total annual use of 6 weeks or less. Pregnant and breast-feeding women, children, the elderly, individuals with chronic illnesses, and individuals with known or suspected alcoholism or liver diseases should avoid using it.

Side Effects

When applied to the skin for long periods or in high amounts, comfrey may be associated with abdominal pain, loss of appetite, and tiredness.

Handling the leaves of the comfrey plant may result in irritation of the hands.


Reportedly, phenobarbital may accelerate and/or increase the formation of toxic chemicals from comfrey under laboratory conditions.

If comfrey is used at the same time as other herbals that could cause liver damage, the risk of liver damage may be increased.


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(Note: The above information is not intended to replace the advice of your physician, pharmacist, or other healthcare professional. It is not meant to indicate that the use of the product is safe, appropriate, or effective for you.)

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