Common Names
- Slippery root
- Knitbone
- Blackwort
- Bruisewort
For Patients & Caregivers
How It Works
Comfrey has not been shown to treat or prevent cancer. Cases of liver toxicity have been reported with its use.
Comfrey leaves and roots have been used for many centuries to treat several ailments, but studies are very limited. Comfrey contains two substances that have been found to be biologically active in laboratory tests: allantoin causes cells to increase the rate at which they divide, and rosmarinic acid reduces inflammation and prevents injury to the small blood vessels in the lungs. Other lab experiments suggest wound healing with a topical formula. However, these effects have not been confirmed in humans through clinical trials.
Many cases of liver toxicity have been reported with use of comfrey. Comfrey has also been confused with foxglove, a poisonous plant, which has resulted in several cases of accidental poisoning.
Purported Uses
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To treat bronchitis
There is no scientific evidence to support this claim. -
To treat pain
A review of herbal medicine for low back pain did not find sufficient evidence for topical use of comfrey. -
To treat cancer
This claim is not backed by research. -
To treat peptic ulcers
There is no scientific evidence to support this. -
To improve wound healing
Laboratory studies show that comfrey leaves have wound healing effects. Human data are lacking.
Patient Warnings
- In 2001 the U.S. Food and Drug Administration, along with the Center for Food Safety and Applied Nutrition, advised all dietary supplement manufacturers to remove products containing comfrey from the market.
- Comfrey contains compounds that are toxic to the liver and can cause liver cancer.
- Comfrey has been confused with foxglove, a poisonous plant, which has similar leaves. Consequently, several cases of accidental ingestion of what was thought to be comfrey herbal tea occurred, resulting in accidental poisoning and death in one case.
For Healthcare Professionals
Clinical Summary
Comfrey is a fast-growing plant whose leaves and roots have been used for centuries to treat many ailments, especially for wound healing. Preclinical studies suggest that oral comfrey has antiproliferative effects (13), and a topical formulation showed wound healing properties (16).
Studies in humans are very limited. Topical formulations of comfrey root extract may relieve acute back pain (14) (17) and knee osteoarthritis (18), but a Cochrane Review of herbal medicine for low back pain did not find sufficient evidence for its use (21).
Comfrey contains pyrrolizidine alkaloids that are both hepatotoxic and carcinogenic (13), and there is extensive literature concerning hepatotoxicity with use of oral comfrey (5) (6) (7) (8) (9) (10). In addition, several cases of ingestion of what was thought to be comfrey herbal tea resulted in cardiac glycoside poisoning due to misidentification with foxglove as the leaves of both plants look similar (15) (22) (23). The risk of systemic absorption following the use of topical comfrey preparations is not known.
Comfrey was used since the 1930s for animal feed, but has been prohibited in Australia and New Zealand. In June 2001, the FDA asked all manufacturers to remove products containing comfrey from the market (12).
Mechanism of Action
The mechanism of action has not been elucidated, but the therapeutic properties of comfrey are thought to be based on its anti-inflammatory and analgesic properties. Comfrey was shown to stimulate granulation and tissue regeneration, and support callus formation (18). Allantoin and rosmarinic acid, two important components, are believed responsible for cell proliferation and anti-inflammatory effects (20).
Warnings
- In 2001, the U.S. Food and Drug Administration along with the Center for Food Safety and Applied Nutrition, advised all dietary supplement manufacturers to remove products containing comfrey from the market (12).
- Comfrey contains unsaturated pyrrolizidine alkaloids, which are hepatotoxic and hepatocarcinogenic (12).
- Comfrey has been confused with foxglove, a poisonous plant, which has similar leaves. Consequently, several cases of accidental ingestion of what was thought to be comfrey herbal tea occurred, resulting in cardiac glycoside poisoning and death in one case (15) (22) (23).