Is Comfrey Edible?

Is Comfrey Safe to Eat?

Common and Russian comfrey

Common comfrey (left) with cream flowers and Russian comfrey (right) with pink flowers.

Common comfrey is a wild-growing herb that has a long tradition as both an edible and a medicinal species. It is a nutritious plant, being very high in Vitamin A, riboflavin, potassium, manganese and dietary fibre, and also a source of other vitamins and minerals such as magnesium and selenium needed by our bodies. It isn’t eaten a lot, as it has a slightly hairy, rough texture as the leaves age, but the young leaves and buds are very tender and delicious in recipes such as Comfrey Leaf Lemonade Fritters. The leaves are used a lot as a herbal tea.

In herbal medicine, comfrey is often used to repair damaged joints, broken bones and torn tendons. This is because comfrey is very high in both vitamin K and vitamin K2 which promote fracture healing (Hodges, 1995). The name comfrey comes from the Latin ‘confera’ which means to knit together, hence the old country name for comfrey of Knitbone. Comfrey root ointment is used to treat painful osteoarthritis of the knee. A clinical trial showed that the ointment works significantly better than a placebo ointment, with five times the effect in pain reduction and four times improvement in quality of life (Grube, Grünwald, Krug & Staiger, 2007).

Napiers Comfrey Salve

Comfrey is often used in ointments such as this Napiers Organic Comfrey and Hypericum Soothing Salve

It is also used in cosmetics because comfrey contains substances that help skin regrow, including allantoin, rosmarinic acid and tannins.

Although herbal medicines are widely considered by the scientific community to be of lower risk than synthetic drugs, they can still sometimes cause toxicity or side effects (De Smet, 2004).

What are pyrrolizidine alkaloids (PAs)?

You may have found  warnings or restrictions on the internal use of comfrey on the internet. This is because comfrey contains pyrrolizidine alkaloids (PAs). Pyrrolizidine alkaloids are a group of 660 phytochemicals found in over 6,000 plants. PAs can also found in honey, grains, milk, offal and eggs. In the case of some species of comfrey, a particular PA called echimidine has caused concern as it is toxic to the liver in animals. Due to this, medicinal or food products for internal use containing comfrey root, are restricted in many countries, with a few also restricting comfrey leaf, although it contains far fewer alkaloids.

The species really matters!

Comfrey Leaf Fritters

My homemade Comfrey Leaf Fritters made from common comfrey (Symphytum officinale).

There are several species of comfrey plant. I only eat common comfrey,  Symphytum officinale (leaf not root) which does not contain echimidine. Symphytum officinale is allowed in over-the-counter preparations in the USA, UK, Canada, Germany. Canada’s Food and Drug Regulations prohibits the sale, for medicinal purposes, of any products containing echimidine (Canada Gazette, 30 March 1988). Canada’s Cosmetic Regulations ban Symphytum species EXCEPT for Symphytum officinale which is allowed. Echimidine, considered to be the most toxic of the PAs found in comfrey (Brauchli-Theotokis 1987), is rarely found in most samples of common comfrey (Symphytum officinale L.) (Couet et al. 1996; Roitman 1981).

Look at the photo at the top of this post – it shows the difference between common comfrey and Russian comfrey. Here in Scotland, common comfrey is predominantly cream flowered which helps with identification but in other areas both have pink-purple flowers and greater car is needed in identification, especially as they do cross-breed. As you’ve read, it is critically important to specify the comfrey species.

I eat, and British herbalists use, common comfrey Symphytum officinale. Please see the following excerpt from American Botanical Council research in 1994 when the first concerns were raised.

“The first Canadian action was taken in 1982, when the Health Protection Branch of Health and Welfare Canada introduced an amendment to Canada’s Food and Drug Regulations which prohibits the sale, for medicinal purposes, of any products containing echimidine (Canada Gazette, 30 March 1988).

Echimidine, considered to be the most toxic of comfrey PAs (Brauchli-Theotokis 1987), is not found in common comfrey (Symphytum officinale L.). However, it is present in prickly comfrey (S. asperum Lepechin) and its hybrids with S. officinale (Huizing, Gadella, and Kliphuis 1982), including Russian comfrey (S. x uplandicum Nyman), which is the most commonly encountered commercial comfrey in Britain (Clapham, Tutin and Warburg 1962).

The intent of this legislation is to have more careful attention paid to identification of botanical species by the herbal industry, and to alert the Canadian public to the potential danger of PA consumption. There was no intent to underestimate the relative potential danger of echimidine-free S. officinale. Both root and leaf of Symphytum officinale have been shown to be carcinogenic in rats (Hirono et al. 1978), though here again there is species confusion because the authors equate common comfrey and Russian comfrey!”

Animal testing – is it like for like?

These theoretical dangers quoted above in Hirono et al. 1978 are not without controversy. Dangerous actions are sometimes attributed to herbs because of in vitro or animal studies. And yet many papers which demonstrate that in vitro or animal actions cannot always be replicated in vivo. Animals and humans are not the same. In the Hirono study, the researchers found that forcing baby rats to eat huge quantities of ground comfrey leaves and roots did them no good at all. Of note, out of 28 rats fed 8% of diet as dry weight comfrey, one showed a liver tumour at 600 days (a long life for a rat!). The average adult human would need to ingest 20,000 comfrey leaves to produce a comparative dose. Assuming 3 dried leaves of comfrey per cup of leaf tea, this equates to drinking 6,666 cups of tea. If you drank a cup of comfrey leaf tea every single day, it would take you over 18 years to reach this level of consumption!

The part of the plant also matters – leaf not root

“Health and Welfare Canada has for many years refused to register comfrey root products for any medicinal application, in recognition of the much greater risk presented by root material as compared to leaf. Comfrey root has been consistently observed to contain roughly ten times the concentration of PA found in leaves (Mattocks 1986, Roitman 1981). Manufacturers have been advised that the inclusion of comfrey root in herbal preparations is no longer acceptable.” Again, this refers to the root not the leaf.

Research can be contradictory

Comfrey was banned in Australia because of a paper called, The Structure and toxicity of the alkaloids of Russian comfrey (S. x uplandicum) a medicinal herb and item of human diet by Dr. C. Culvenor, et al, Australia, 1980. Although Culvenor and his associates identified eight alkaloids in comfrey, four being new to science; there does seem to be inaccuracy, when he quoted the results of Pederson (1975 ). Quotes indicated that he found a 9% concentration of alkaloids in leaves, when Pederson’s actual figures were 0.9 parts per thousand when estimated by titration, and 1.9 parts per thousand when estimated gravimetrically.

Theoretical dangers are often attributed to herbs because of the singular action of one constituent, although herbs are a complex blend of hundreds of phytochemicals whose combined beneficial and protective action negate this. For example, meadowsweet contains salicylic acid (naturally) which is what aspirin is made of (chemically). Aspirin can upset stomachs yet meadowsweet is used by medical herbalists to treat stomach ulcers. Meadowsweet, unlike aspirin, contains many other phytochemicals which have a soothing effect.

Read more here about the use of comfrey in creams and ointments.

Using comfrey in pregnancy

Warnings about use in pregnancy, breast-feeding and children found on medicinal/drug advice websites will always caution against use in these conditions without the advice of a doctor unless specific clinical trials have been done on children or pregnant women – which they rarely are! So this is a default warning. To be quite honest very few doctors would even know the answer as without specific genotox/clinical trials this information does not exist. To be on the safe side, pregnant or breastfeeding women should not eat or drink comfrey. Externally, the tiny amount used in a cosmetic cream would be negligible.

Reported side effects

There have been some side effects reported from:
• taking comfrey medication (species not recorded) – a woman (1985) taking two comfrey medicines, one for four months and one for six months, and 2 women (1987) who took comfrey-pepsin tablets for 6 months.
• drinking comfrey tea (species not recorded) – a boy with Crohn’s disease (1987) who regularly drank comfrey tea and a woman (1989) who drank 10 cups of comfrey tea daily for 4 years
• eating comfrey  (species not recorded) – one single case of a man (1990) who ate 4-5 cooked comfrey leaves a day for 2 weeks  where comfrey may have contributed to his death by liver failure.

These case studies do support that underlying illness, poor nutrition and the concurrent use of hepatotoxic drugs, increase the likelihood that veno-occlusive (liver) disease may develop when using PA-containing drugs or eating PA-containing plants (Rode, 2002).

To put this in perspective, according to the Office for National Statistics, between 1993 and 2011 around 23,630 people have died in the UK from drug-related poisoning not including drug misuse! (The total deaths if you include drug misuse being 52,732.) Where the cause of death is mentioned on the death certificate, this includes:
• 8606 deaths due to paracetamol poisoning
• 8324 deaths due to antidepressants
• 4611 deaths due to benzodiazepines (Diazepam (Valium), Temazepam and Nitrazepam
• 3079 deaths due to Tramadol
• 872 deaths due to aspirin

Note for people taking medication

An obvious recommendation with comfrey is not to eat or drink it excessively. I would add that you should definitely not eat it if you already take a drug that is known to harm the liver. This includes: acetaminophen (Tylenol and others), amiodarone (Cordarone), carbamazepine (Tegretol), isoniazid (INH), methotrexate (Rheumatrex), methyldopa (Aldomet), fluconazole (Diflucan), itraconazole (Sporanox), erythromycin (Erythrocin, Ilosone, others), phenytoin (Dilantin), lovastatin (Mevacor), pravastatin (Pravachol), simvastatin (Zocor), and many others. If you are on other medication, especially carbamazepine (Tegretol), phenobarbital, phenytoin (Dilantin), rifampin, or rifabutin (Mycobutin), speak to your doctor or medical herbalist before using comfrey, as like other herbs, it may compete with the drug in your liver, the combination of which can cause side-effects.

Why I eat comfrey

There are many issues with the way that research is reported on the internet and many people scare themselves by reading badly referenced and poorly interpreted reports. I eat comfrey personally because I cannot find a single published case history of a healthy human actually experiencing (as opposed to theoretically being at risk from) liver damage from eating identified common comfrey. Nor do I intend to ever consume 20,000 leaves nor drink a cup a day for 18 years.

I’m not saying that comfrey is totally safe or denying the presence of PAs. That would be to discredit science and just be ignorant! However, it is all a question of perspective. I believe that I will be doing less harm to my body by occasionally eating or using comfrey than I would from, for example,  drinking caffeinated drinks daily, eating processed foods full of chemicals, eating non-organic food sprayed with pesticides, breathing in fragrance chemicals from electric “air fresheners”, traffic fumes, pharmaceutical drug side-effects… the list goes on.

Significantly, a trial by Dr. Clare Anderson, from the Laboratory of Pharmakinetics and Toxicology, School of Medicine, University College, London, tested forty long-term comfrey consumers, who then submitted for liver function tests (Anderson, 1981). This was a small group for a clinical trial but with prolonged consumption of comfrey leaf (0.5–25 g day for 1–30 years). All were found to have perfectly fit livers!

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Author

Monica Wilde, 2014Monica Wilde works at Napiers the Herbalists. She is a Research Herbalist with a Masters Degree from UCLAN and an advocate for quality, safety and research in herbal medicine. Her special interest is researching drug-herb interactions. At weekends, Monica runs foraging courses and events specialising in wild food and wild medicine.

Podcast

Robin Harford of Eatweeds.co.uk has recorded a Podcast interview with Monica speaking about comfrey. Click here to listen. It is the second interview on the Podcast.

References

Anderson, C. (1981) Comfrey in Perspective. The Lancet, 1(8235): 1424
Couet, C., Crews, C. & Hanley, A. (1996) Analysis, separation, and bioassay of pyrrolizidine alkaloids from comfrey (Symphytum officinale). Nat Toxins. 4(4):163-7. PubMed PMID: 8887946.
De Smet, P. (2004) Health risks of herbal remedies: an update. Clin. Pharmacol. Ther., 76: 1–17
Grube, J., Grünwald, L., Krug, C. & Staiger. (2007) Efficacy of a comfrey root (Symphyti offic. radix) extract ointment in the treatment of patients with painful osteoarthritis of the knee: Results of a double-blind, randomised, bicenter, placebo-controlled trial. Phytomedicine, 14: 2-10
Hodges, S., (1995) Comfrey root & bone healing.Bone, 16(3): 405
Pedersen (1975) Arch. Pharm. Chem. Sc. Ed. 3: 55-64
Rode, D. (2002). Comfrey toxicity revisited. Trends in Pharmacological Sciences, 23(11): 497-499
Roitman JN. (1981) Comfrey and liver damage. Lancet. 1(8226):944. PubMed PMID: 6112346.

23 Comments

      • I have a comfrey question I’ve not been able to find the answer to: My bees love comfrey nectar, but is it making their honey unsafe for me to eat?

        • Honey already contains PAs but we’ve been eating it for hundreds of thousands of years so I wouldn’t worry. According to Wikipedia: “It has been estimated that 3% of the world’s flowering plants [circa 6,000] contain pyrrolizidine alkaloids. Honey can contain pyrrolizidine alkaloids, as can grains, milk, offal and eggs.” Reductionist science doesn’t always work with plant effects as they contain numerous protective biochemicals as well.

  1. lesley swain

    A well researched and thought through piece.
    I’ve been eating comfrey leaf frittatas since I was a tiny kid and I’ve made it to 50+ with a proven healthy liver (due to a brush with viral hep I’ve had plenty of liver function tests and biopsies and my liver is fine!!!). As you say, it’s crucial to recognise common comfrey (Russian comfrey is rare outside gardens in the UK) and also – I would add – to know about preparation and possible s/e’s.

    • Thanks Lesley, and cheers for letting me know about your liver 🙂 Russian comfrey is starting to make more of an appearance, and it does hybridise so needs to be kept an eye out for. Actually I think that there is more trouble with people mistaking foxglove for comfrey and getting ill from foxglove poisoning, than there are reports of comfrey side effects on the liver!

      • lesley swain

        Any hybridisation I see is usually very close to gardens………but I’d agree that – certainly in the UK – there are more poisonings reported due to consumption of foxglove (accidental or otherwise) than there are reports of even mild hepotoxicity from comfrey consumption. In my limited experience it’s often the case with actual reports of such that the linking of Comfrey consumption and concurrent toxic hepatitis is a paper exercise with comfrey being assumed to be the cause since little else can be found……….locally there was a rash of reports of milk thistle affecting liver function tests in the mid 90s, but it later transpired that the consumption of milk thistle was DUE to folk seeking relief from liver-based symptoms (hep c) rather than the causal agent. I sometimes wonder how many links are erroneously formed between many medications – herbal or otherwise – and clinical symptoms simply because the consumption of one is present during the experiencing of the other…..
        Having said that I’d like to see more scientific and fact based evidence on comfrey.

  2. Is the flower colour an absolute in telling the two apart. Also the common comfrey leaf shape seems rounder the russian more spear shaped, is this a reliable trait to use when the flowers aren’t out (if this is so I think the russian is also spreading along river banks – i guess an accelerated vector from back gardens. Finally is the relative pricklyness useful in IDing? Many thanks for the article

    • Yes the flower colour is an absolute in telling the two apart… except in hybrids! Look up the Symphytums here http://www.ukwildflowers.com/Web_pages_intros_indexes/latin_index.htm#S though because there are also a few other comfreys (caucasian comfrey – blue flowers) (tuberous comfrey = creamflowers/brown tip) that you need to be aware of it only using flowers as ID. The common comfrey leaf shape is rounder, also paler, livelier green with cream decurrent veins while the Russian is more spear shaped, darker, more blue-green with dark veins. Common is shorter and a friendlier looking plant, Russian is bigger, bullish and bristlier (your ‘relative prickleyness’). Luckily even if you have a few meals out of the ‘wrong’ comfrey, you will be fine!

      • Interesting: trying to figure out based on this info why this site

        https://www.horizonherbs.com/product.asp?specific=1922

        is listing this plant as officinalis, and specifically “low in pyrrolizidine alkaloids” when the plant appears by most of your described identifiers to be russian comfrey and not common or true comfrey at all….

        any thoughts before I abandon the site as an unreliable source?

        • Here in Scotland the majority of common comfrey has cream flowers so is a really easy way of making sure you don’t have Russian comfrey. However, it’s not the same everywhere. I know down in Dorset they are mainly pink-purple flowered. I would guess this is the same in the USA. It makes positive ID much trickier especially as russian comfrey, being a hybrid between officinalis and asperum, is variable. Rough comfrey (S. asperum) is also blue-pink flowered.

    • Yes they are equivalent. The difference in strength varies because of growing season, area, conditions and the root is stronger than the leaf, more so taken internally. In a licensed medicine produced under GMP the plant strength is monitored and products produced consistently. In unlicensed products, cosmetics and home made products there will be fluctuation.

  3. Very interesting article, thank you. The American herbalist Susun Weed – who is an advocate of comfrey leaf use internally and externally – suggests that the Russian comfrey is actually the safe variety, because it has been hybridised and has had the PA levels lowered through selective breeding. She feels that the real issue is that most commercially-available dried comfrey is mislabelled (as officinale when it’s actually uplandicum).
    http://www.susunweed.com/herbal_ezine/June08/wisewoman.htm
    Can you clarify?

    • Hi. I read Susun’s article http://www.susunweed.com/herbal_ezine/June08/wisewoman.htm and have to disagree with her comments about common comfrey (S. officinale) which British herbalists use, based on the research I have had access to. She specifically talks about her experience with Russian comfrey (Symphytum uplandicum) – in the USA “Symphytum uplandica x” – used by American herbalists, which is both a hybrid between S. officinale and Rough Comfrey (Symphytum asperum) and to confuse matters further, also commonly hybridises itself. Echimidine is more likely passed on by S. asperum as this has also tested positive in the past.

      But the point Susun is making is very valid. When tested, the leaves she had were not found to contain any significant levels of PAs.

      However, we’re splitting hairs as even where comfrey leaves do contain PAs, biochemist Bruce Ames gives one cup of comfrey tea the same HERP carcinogenic risk factor (0.03%) as a peanut butter sandwich! Still lower than 1 bottle (354ml) beer at HERP 2.8% or 1 glass (250ml) of wine at HERP 4.7% (Science, 1987).

      The moral of the tale is that it is probably not wise to make comfrey, peanut butter sandwiches, beer or wine a “significant part” of your regular diet for an extended period of time.

      References
      Ames., BN., Magaw, R., & Gold, LS. (1987) Ranking possible carcinogenic hazards. Science, 17(236), 4799, 271-280. DOI: 10.1126/science.3563506
      http://toxnet.nlm.nih.gov/cpdb/pdfs/Science-Ranking.pdf

      • Thanks for the fast reply, Monica!

        Another example of the US and UK being divided by a common language, I guess – and made even more complicated where botanical terms are concerned. Reassuring information, however. I follow Susun’s recommendation of drinking herbal infusions daily and I probably have about 2 pints of comfrey infusion a week which means most days are comfrey-free, so I’ll relax and continue (especially since I don’t drink beer or eat peanut butter!).

        Thanks for the great site – I’m from Scotland originally, living in England now, but I’ll keep an eye on your course dates for the next time I’m up visiting the family…

  4. I consumed Comfrey tea to treat my Crohns, it was quite helpful and I didn’t get any side effects from drinking it.

  5. Hi Monica,

    Amazing article, thanks a lot for sharing your knowledge.

    I hope you don’t mind me asking questions about comfrey. I am planning to plant some in my garden, since I don’t want it spreading all over the place, I would like to use bocking 14, which I believe is seedless and therefore easier to control.

    I have been researching and it seems that bocking 14 is a hybrid between common and Russian comfrey. Would that be this hybrid low in alkaloids, and therefore safe for human consumption?

    Thanks a lot for your time, and regards from North Edinburgh!

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