- Side Effects
- Drug Interactions
- Pregnancy & Breastfeeding
- What Else to Know
Generic Name: comfrey
Other Names: black root, blackwort, bruisewort, common comfrey, gum plant, healing herb, knitbone, prickly comfrey, salsify, slippery root, Symphytum officinale, wallwort
Drug Class: Herbals
What is comfrey, and what is it used for?
Comfrey is a plant, Symphytum officinale, native to Europe and Western Asia, now also grown in North America.
Comfrey leaves, roots, and rhizomes have been traditionally used for varied medicinal purposes such as local application for skin ulcers, joint and muscle pains, fractures, and osteoarthritis. Comfrey has also been taken orally as herbal teas, root powders, and capsules for gastrointestinal conditions, menstrual disorders, cough, and bronchitis.
The medicinal effect of comfrey is from some of the substances it contains such as allantoin, rosmarinic acid, and tannins, which may help regeneration of skin and reduce pain and inflammation. Comfrey, however, also contains pyrrolizidine alkaloids, toxic compounds that can cause severe liver damage, cancer, and death. Pyrrolizidine alkaloids damage the endothelial cells that line the blood vessels in the liver, and cause liver injury and blockage of the liver’s veins (veno-occlusive disease).
Topical comfrey may reduce inflammation and pain from bruises, and muscle and joint pain, but systemic absorption from topical application can also lead to toxicity and serious adverse effects. There is little scientific evidence to support any of comfrey’s uses, topical or oral, especially considering the risk of potentially serious side effects. There have also been instances of comfrey being confused with similar-looking leaves of foxglove, another poisonous plant, which resulted in heart damage from glycoside poisoning and death in one case.
In 2001, The FDA, along with the Center for Food Safety and Applied Nutrition, released an advisory recommending the removal of all comfrey products from the market. Oral comfrey is banned or restricted in most countries, although topical comfrey is still available in cream and ointment formulations.
Comfrey has been used for:
- Skin ulcers
- Wound healing
- Rheumatoid arthritis
- Muscle and joint pains
- Varicose veins
- Peptic ulcers
- Heavy menstrual periods
- Bronchial inflammation (bronchitis)
- Persistent cough
- Gum disease and sore throat (gargle)
- Never take comfrey orally, it contains toxic alkaloids that can damage the liver.
- Never administer comfrey to a child, orally or topically.
- Do not apply on broken or damaged skin, it can increase the risk of systemic absorption and consequent toxicity.
- Do not use comfrey if you have liver disease.
What are the side effects of comfrey?
Common side effects of comfrey include:
- Liver damage
- Liver enlargement
- Veno-occlusive disease
- Decrease in urine output
- Abdominal pain
- Abdominal distension
- Loss of appetite (anorexia)
Call your doctor immediately if you experience any of the following symptoms or serious side effects while using this drug:
- Serious heart symptoms include fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness;
- Severe headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady;
- Severe nervous system reaction with very stiff muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, and feeling like you might pass out; or
- Serious eye symptoms include blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.
This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.
What are the dosages of comfrey?
- Not recommended for internal or limited topical use because of the content of hepatotoxic pyrrolizidine alkaloids
- Historically, daily doses of leaf ranged from 5 to 30 g
- Comfrey contains toxic compounds that can cause liver and lung injury, resulting in damage to the veins and blockage of blood flow (veno-occlusive disease), and cancer. Treatment may include symptomatic and supportive care.
What drugs interact with comfrey?
Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.
- Comfrey has no known severe or serious interactions with any other drugs.
- Moderate interactions of comfrey include:
- Comfrey has no known mild interactions with any other drugs.
The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.
It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.
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Pregnancy and breastfeeding
- Comfrey contains toxic alkaloids. Do not take orally or apply topically if you are pregnant or breastfeeding.
What else should I know about comfrey?
- Do not take comfrey orally, it is toxic and can damage the liver. The FDA has recommended removal of all oral comfrey products from the market.
- Systemic absorption from the topical application can also be toxic and likely unsafe. If you use topical comfrey products:
- Follow manufacturer’s directions exactly
- Use only small amounts for no longer than 10 days at a time
- Do not use for more than 4 to 6 total weeks in one calendar year
- Store safely out of reach of children
- Seek medical help or contact Poison Control in case of overdose
- Check with your healthcare provider before using any herbal product.
- Herbal products do not undergo rigorous evaluation by the FDA for safety and efficacy. Products may differ in formulations and strengths, and labels may not always match contents. Exercise caution.
Comfrey leaves, roots, and rhizomes have been traditionally used for varied medicinal purposes such as local application for skin ulcers, joint and muscle pains, fractures, and osteoarthritis. Common side effects of comfrey include liver damage, liver enlargement, veno-occlusive disease, decrease in urine output, lethargy, abdominal pain, abdominal distension, and loss of appetite (anorexia). Comfrey contains toxic compounds that can cause liver and lung injury. Do not take if pregnant or breastfeeding.
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