People have long been amazed by the benefits of comfrey and its ability to heal wounds and broken bones. In the 17th century, herbalist John Parkinson said that comfrey was so amazing for knitting together flesh that if you put two pieces of severed flesh in a pot with comfrey, they would be joined together again. While I doubt this, I have no doubt that comfrey is a powerful wound healer – I’ve seen it work with my own eyes.
However, before we dive into the benefits of comfrey, I have to address the comfrey controversy…
Mention comfrey in a room full of herbalists and you’ll most likely be front seat to a heated discussion. Everyone’s got an opinion regarding the safety of comfrey, and most herbalists aren’t shy about expressing it.
For years, I’ve watched the comfrey debate from afar, and noted that many herbalists will refer to someone else when justifying their opinions: “So and so says comfrey is safe, so it must be true.” “Well, this other person says it’s not safe so that must be true.”
While I have no doubt the comfrey debate will continue to rage on for a long time, I want to address this issue as objectively as possible by looking at what evidence we have of its safety and what evidence we have of its potential for harm. My hope is that people will have a better understanding of the complexities of this herb, rather than a “he said, she said” contest.
Comfrey has been shown to contain pyrrolizidine alkaloids (PAs), which are substances that we know are potentially toxic to humans by causing liver damage. There are over 600 different PAs that have been identified in over 6,000 plants.1 Many PAs are harmless, but those that are harmful take quite a toll on the liver, causing veno-occlusive liver disease and/or liver cancer. PAs are found in the borage, aster, orchid and pea families and are a plant’s defense against being eaten by herbivores.
While rats that are unethically fed large amounts of comfrey leaves have been shown to develop liver cancer, the main concern in humans is veno-occlusive disease (VOD). This condition happens when the very small (microscopic) veins of the liver are obstructed, preventing normal liver function and causing a backup of blood in the liver, leading to engorgement, portal vein pressure, fluid buildup in the abdomen (ascites), enlarged spleen, and liver scarring (cirrhosis). Symptoms occur very quickly. About one-fourth of the people diagnosed with hepatic VOD die.2
Contrary to some herbalists' claims, we know without a doubt that all species of comfrey contain varying levels of several different types of PAs.3
The two most often discussed species of comfrey are Symphytum officinale (common comfrey) and Symphytum x uplandicum (Russian comfrey, a hybrid). We know that Symphytum x uplandicum contains more PAs than Symphytum officinale.4 However, because plants can easily hybridize within the genus, it’s hard to say whether a given plant has a certain level of PAs unless that exact plant has been tested.
One set of tests done in 1980 showed that there were significantly lower levels of PAs in Symphytum officinale leaves after the plant had matured and gone to flower. Studies also show that the leaves reliably have fewer PAs than the roots.5
I’ve also heard herbalists claim that water extractions (such as teas) do not contain PAs. However, in one analysis of herbal teas made from the leaves of comfrey (Symphytum officinale), we see that there are PAs present in the tea.6
As a rule, I avoid citing unethical animal studies in my articles. There have unfortunately been a number of studies of comfrey involving rats. I will not cite them here, but only acknowledge they exist and that when you feed rats large amounts of comfrey, they will get a liver tumor.
I have heard herbalists point out the flaws of using these studies (e.g., rats are not humans, the dosage was insanely high) and then claim that since these studies are flawed, then comfrey must be safe. The reality is, even if you completely disregard these animals studies, there is still evidence that comfrey is potentially harmful to humans. In the same light, using only these flawed studies to proclaim comfrey dangerous is misleading.
To date, there have been no human clinical trials regarding comfrey ingestion. Since there are concerns about comfrey toxicity, you can imagine the ethical considerations a human clinical trial would raise.
One author suggests that we study people already using comfrey regularly. “Perhaps the most direct approach to assessing the benefits and attendant risks of the therapeutic use of comfrey would be to screen the current population of comfrey users. A direct determination of risk would offer the greatest protection to individuals currently consuming comfrey, and provide the information required for placebo-controlled prospective clinical studies designed to determine efficacy and define safe use.”7
I found four case studies implicating comfrey ingestion in VOD. In all of these case studies, comfrey does appear to have caused problems, but there are also multiple confounding factors, such as concomitant use of hepato-toxic drugs and malnutrition.8,9,10,11
You can read more about these case studies here.
So far I have done my best to report what we know about comfrey from scientific tests and case studies. I would like to briefly summarize the debate about comfrey amongst herbalists.
On one side, we see herbalists claiming there is potential for harm when taking comfrey internally, and therefore it must be avoided. Some herbalists recommend comfrey with precautions, such as only using the mature leaf internally (never the root) and for short periods of time.
On the other hand, some herbalists claim that they have either taken or recommended comfrey internally for extended periods of time with no problems, and therefore their experience tells them comfrey is safe.
Unfortunately, due to the nature of VOD, it is very difficult to link PA-containing plants to the symptoms. PAs could be called a “silent killer,” since very few of their victims will recognize the cause of their liver disease. As Paul Bergner points out, “Pyrrolizidine alkaloid poisoning was only discovered in 1954. It is insidious, and can take from 2-13 weeks for onset of symptoms, even after stopping ingestion. In the various epidemics and single cases around the world, none of those who consumed them suspected the plants as the cause. Note that these cases have involved plants used in Ayurvedic medicine, traditional Chinese medicine, traditional African medicine, and folk medicines of Jamaica and Mexico. The Eclectic doctors – careful clinicians – never noted the toxic effects of Senecio spp., now acknowledged by scientists and herbalists alike.”12
Why thanks for asking! To echo Paul Bergner, I feel there is a rare, but real, risk when using comfrey leaves internally. But beyond my opinion, the scientific evidence and case studies seem to confirm that the risk is real.
There are herbalists, like Susun Weed, who have been using and recommending comfrey leaf infusions internally for decades, so we know that some people can use it without developing liver disease – or at least that liver disease is not yet visible. Yet there are many unknowns. What if someone happens to use leaves from a plant that is very high in toxic PAs? What if someone has preexisting unknown (or known) liver issues and the comfrey puts them over the edge into liver disease? What if comfrey’s PAs interact with certain circumstances or genetics to cause more damage than they otherwise would?
Without a doubt, neither comfrey root nor leaf should be used during pregnancy, breastfeeding, or in small children with developing livers. However, as a clinical herbalist I do not feel that it is ethical to recommend to anyone a plant that has the potential for serious problems, at least not until we know more.
As far as we know, it is entirely safe to use comfrey externally.13 There luckily are many topical applications where comfrey is very useful. Now that we’ve looked at the controversy, let’s spend some time looking at the many benefits of comfrey.
[Comfrey] simply is the best herb for healing external wounds, broken bones, and treating knocks and falls.
Thomas Avery Garran
Western Herbs in Chinese Medicine: Methodology and Materia Medica
Above all, comfrey is a supreme healer of the body’s connective tissues: the skin and bones. It works amazingly well for everything, from little scratches and rashes and boo-boos, to more serious cases such as eczema, skin ulcers, sprains, broken bones, rheumatic complaints, and healing from surgery.
Most herbalists have amazing comfrey tales to tell and I’ve racked up a few of my own over the years. I’ve seen my mother-in-law avoid knee surgery (to the amazement of her doctor), a second-degree burn on my thumb that was immediately soothed and then completely healed within 24 hours, and countless minor cuts and bruises restored in record time.
But you don’t just have to take my word for it – there are multiple clinical trials validating comfrey’s wound healing abilities. In one randomized double-blind clinical study, 278 patients used either a comfrey cream or a placebo on fresh abrasions. Those using the comfrey cream healed almost three days faster than those using the placebo.14 Comfrey has also been shown to work well for healing bruises and contusions in children.15
How does it work? Comfrey is a cell proliferant. It increases cell growth and rejuvenation (granulation), thus propelling the healing action of the body. Many herbalists cite its chemical constituent, allantoin, a known cell proliferant, for this ability. However, one study compared the healing abilities of a water extract of comfrey root vs. pure allantoin and concluded that, “the biological activity of the comfrey root extract cannot be attributed only to allantoin, but is also likely the result of the interaction of different compounds present in AECR [aqueous extract of the comfrey (Symphytum officinale L.) root].”16
Comfrey can also powerfully heal burns. I first learned about using comfrey root on burns from Kimberly Gallagher. I would never want to be without it, as it has soothed many of my own minor burns since. She takes the fresh root and blends it with a bit of water in a blender or food processor. The resulting slurry is put into a cardboard juice concentrate container and stored in the freezer. When it’s needed, you simply peel back the cardboard and cut off a bit of the frozen root with a sharp knife. Apply that to the burned area, replacing it with more frozen root as needed. Prepare to “ooh” and “ahh” as the comfrey root magically stops the burning pain and heals the skin quickly.
I’ve also seen the topical use of comfrey significantly address swelling. An acquaintance of mine was stung by a wasp and, as a result, her arm had significant swelling. By the time she asked for my advice, it had been swollen for days. She ended up using comfrey as a bath for her arm, and the swelling reduced almost immediately.
Comfrey’s ability to modulate inflammation and decrease pain in musculoskeletal injuries and general pain dysfunction has also been well studied. In one randomized, controlled, double-blind clinical study, a topical cream made with comfrey was used for patients with general back myalgia (muscle pain). Those using the concentrated comfrey cream had decreased pain on active motion during rest and palpation, and healed faster than those using the reference product.17
In another clinical trial with patients who had low back pain, 95.2% of those using a topical comfrey cream had decreased pain, as opposed to 37.8% of those using the placebo cream.18
Comfrey has been shown to decrease pain and swelling in acute trauma. In one controlled, double-blind, randomized multicenter study, 203 patients with ankle sprains were given either a comfrey cream or a placebo cream to use topically. Patients using the comfrey cream saw a highly significant decrease in pain and swelling by days three and four.19
Comfrey root has been shown to be effective for patients with osteoarthritis of the knee. One randomized, double-blind, bicenter, placebo-controlled clinical trial followed arthritis patients who used a comfrey cream daily for three weeks. Those using the comfrey cream had significant improvements over those using the placebo. They concluded that, “The results suggest that the comfrey root extract ointment is well suited for the treatment of osteoarthritis of the knee. Pain is reduced, mobility of the knee improved, and quality of life increased.”20
Both the leaves and the root of comfrey are demulcent, although the root has a much stronger action. If you moisten some powdered root with water, you will immediately feel the slimy, mucilagenous quality.
Before the potential for toxicity was known, comfrey root was used internally for many hot conditions, such as dry, irritated lungs. It was also used for internal bleeding of the lungs and digestive tract, such as ulcers and hemorrhoids.
Comfrey leaves are high in vitamins, minerals, and even protein. Susun
Weed recommends drinking a nourishing herbal infusion made with up to an
ounce of the leaves as a way to enjoy the nutritional benefits. This
practice is highly controversial because of the toxicity concerns. The
leaves of this plant were also once widely eaten as a wild green food,
but this is also discouraged.
Comfrey has been made popular in permaculture practices. The leaves can be used as a mulch, added to the compost pile, or fermented down to a dense green liquid to be used as a potent fertilizer. Comfrey is also being explored as a nutritive forage food for animals.
Comfrey is native to Europe and Asia and likes to grow in sunny moist areas. There are many species of comfrey in the Symphytum genus.
Symphytum officinale (common comfrey) is most often used as medicine. Symphytum x uplandicum (Russian comfrey, a hybrid) is more often used as a garden fertilizer and animal feed. This section describes Symphytum officinale.
Comfrey is a hardy perennial with a strong root base. This plant is practically impossible to kill in temperate regions. You can hack away all of its leaves and even part of its root and it will still grow back.
The leaves are oblong and coarsely textured, with smooth margins.
It flowers in the late spring to summer, with flowers ranging from pink to blue to purple. The flowers are small and bell-shaped, typical of the Borage family. Bees love the flowers.
It can grow up to four feet in height.
Comfrey is easily grown from seed or root cutting in temperate zones. Once you have comfrey in your garden prepare to always have comfrey in your garden.
The safest way to use comfrey is with external applications, including poultices, salves, and fomentations/washes. These preparations are ideally made from the fresh leaves and/or roots.
Comfrey leaves and roots can be preserved in the freezer so that you always have access to it, should a need arise outside of the growing season. To prepare comfrey leaves, place a large amount of chopped leaves in a blender with a bit of water and process to form a thick slurry. Spread this slurry onto an old t-shirt or over several layers of cheesecloth. Cover with another layer of fabric. Place this in a ziplock bag and lay it flat in the freezer. It can then be taken out of the freezer and used as needed. (I recommend using it warm with a hot water bottle placed over it.)
Comfrey can also be extracted into oil. I like to wilt the leaves first and use a hot water bath method to infuse the oil. If you are using fresh leaves in cold oil, check on it daily to push down the plant material beneath the surface of the oil to avoid spoilage. The infused oil can be made into a salve or lotion.
The root can be used when dried. I prefer buying it in a powder and mixing it with water to form a plaster for external use. Preparing frozen comfrey roots is explained above. I don’t recommend using the root internally.
Comfrey is an abundant European plant that may be one of the best herbs for the healing of wounds and addressing a wide range of musculoskeletal complaints, from broken bones to arthritis. Although we are still searching for definitive answers in regards to its toxicity when taken internally, comfrey can still be a powerful ally when used topically.
Special thanks to Thomas Easley for compiling these resources on comfrey.
Rosalee is an herbalist and author of the bestselling book Alchemy of Herbs: Transform Everyday Ingredients Into Foods & Remedies That Heal and co-author of the bestselling book Wild Remedies: How to Forage Healing Foods and Craft Your Own Herbal Medicine. She's a registered herbalist with the American Herbalist Guild and the Education Director for LearningHerbs. Read about how Rosalee went from having a terminal illness to being a bestselling author in her full story here.