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Comfrey Alkaloids: Variations and How to Lessen
I sell live Comfrey roots, seeds, and dried comfrey.
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Alkaloids Vary by Season, Age, Plant Type

Seasonal Variation
"The alkaloid content can also vary from season to season. The amount of alkaloids in Russian comfrey (S. uplandicum) leaves can vary up to 16 times depending on the time of year and the size of the leaf."
(A.R. Mattocks, Lancet, November 22nd 1980 as cited in Botanical Medicine,

Climate, Season, Soil
"It is pertinent to note that the alkaloid content in different parts of the plant (e.g., roots, leaves, stalks, flowers, and buds) varies and is subject to fluctuations according to the climate, soil conditions, and time of harvesting. (Danninger et al., 1983; Hartmann & Zimmer, 1986)."
(World Health Organization, International Programme on Chemical Safety, Environmental Health Criteria 80, Pyrrolizidine Alkaloids, ehc/ehc080.htm.)

Climate, Season, Age, Part/Type of Plant
"Both the composition and concentration of PAs may fluctuate according to climatic and environmental conditions, the age and part of the plant and the variety (genotype/chemotype). The same species growing in different locations or in different seasons may contain different alkaloids."
(European Medicines Agency, document_library/ Public_statement/2012/10/ WC500134311.pdf.)

Alkaloids- More in Root than Leaf, More in Young than Mature Growth

Young leaves have higher Alkaloids than larger, older leaves (and probably more beneficial Allantoin).
Young roots have more than older roots (and probably more Allantion).
Roots have more Alkaloids and Allantoin than leaves.

See my page Comfrey and Healing for more about how roots seem like concentrated leaves, with more bad Alkaloids and good Allantoin. Read the section 'Does More Alkaloids Mean More Allantoin?'.

Mature Leaves Have Fewer Alkaloids.

"It is clear that there are wide differences between concentrations of alkaloids in young and older comfrey leaves."
(FDA Poisonous Plant Database, FDA #: F01188, Symphytum sp., plantox/detail.cfm?id=962.)

"The comments of Mattocks should at least be noted: 'People who consider the benefit of comfrey to outweigh the (perhaps slight) risk involved may like to know that large, mature leaves carry the lowest concentration of toxic alkaloids.'"
(FDA Poisonous Plant Database, plantox/detail.cfm?id=962)

Roots Have More Alkalloids

"Comfrey contains potentially dangerous compounds known as pyrrolizidine alkaloids. The roots contain higher levels of these compounds and mature leaves contain very little, if any, of these alkaloids. Fresh young leaves contain higher amounts (up to 16 times more than mature leaves) and should be avoided."
(K.A. Winship, Toxicity of Comfrey, Adverse Drug Reactions and Toxicological Reviews, 1991;10:47-59, cited by University of Michigan Health System, health-library/hn-2073000.)

Consult your health care provider for advice.

Alkaloids: True vs Russian Comfrey

True Comfrey Has Fewer Alkaloids than Russian

"As expected PA levels in S. officiale (True) were found to be lower than in S. uplandicum (Russian), and small, young leaves contained higher levels of PAs than large, older leaves. Root was found to contain considerably higher content of PAs than leaves."
(Feasibility of Producing Comfrey- Symphytum spp.- Pellet as a Feed Supplement, 1999,

Russian Comfrey (spp.?)

"Mattocks (1980) demonstrated that the alkaloid content of the leaves of Symphytum spp. (Russian comfrey), which are used as an item of food, varies with their maturity. The toxic PA content is highest at the beginning of the vegetative period and declines as the leaves mature. The PA content of the roots is much higher than that of the leaves, and dried leaves contain a higher concentration than fresh leaves (Mattocks, 1986)."
(World Health Organization, International Programme on Chemical Safety, Environmental Health Criteria 80, Pyrrolizidine Alkaloids, ehc/ehc/ehc080.htm.)

The above statement 'Symphytum spp. (Russian comfrey)' is confusing. In botany spp is defined as all species of the genus named (Symphytum). This includes True/Common, Russian, Prickly and many other Comfrey cultivars. It does not mean only Russian Comfrey. This is a common problem in research. Scientists lump one cultivar of comfrey with all the other comfrey cultivars. Yet each is different in constituents and properties.

The last sentence about dried vs fresh leaves contradicts other studies that state drying reduces alkaloids. I think drying would reduce alkaloids. Unless it meant based on weight since fresh leaves would contain a lot of water. Though this goes to show how confusing much research is because they are vague about comfrey cultivar, whether root/leaf, dried/fresh, etc.

The photos of the plates are dried/cut comfrey leaf and powdered comfrey root.

Reducing Alkaloids: Drying

1. Drying roots and leaves reduces alkaloids.

"When comfrey is dried, enzymes are released and much of the alkaloid is destroyed."
(Herbs Are Special, Australia, free-herb-information/comfrey.html)

"Drying the comfrey reduces the amounts of alkaloids."
(Permaculture Reflections, species-of-month-comfrey.html.)

Reducing Alkaloids: Cooking

2. Cooking lowers the alkaloids. Food in the Nightshade (Solanaceae) Family also contain alkaloids. These include tomatoes, peppers, eggplant, and white potatoes. Cooking them reduces their alkaloid content by 40-50%. So probably the same is true for Comfrey.

"The plant alkaloids are highly water-soluble; boiling or steaming the leaves in several changes of water may reduce toxicity."
(Georgetown University Medical Center, urbanherbs/Comfrey.htm.)

"In addition, cooking will ensure some of the soluble alkaloids are lost in the vegetable water."
(FDA Poisonous Plant Database, FDA #: F01188, Symphytum sp., plantox/detail.cfm?id=962.)

Reducing Alkaloids: Silage

3. Making silage out of comfrey decreases alkaloid content. Silage is made by compacting grass or other green fodder. Then storing it in an airtight container such as a silo, garbage bag, or plastic sheeting. It is not dried first. It ferments anaerobically (no oxygen). It is a good ruminant animal feed in winter.

"PAs are largely biodegraded when forages are conserved as silage. A rapid decline in PA concentrations under composting conditions was also observed."
(European Food Safety Authority, Scientific Opinion on Pyrrolizidine Alkaloids in Food and Feed, 2011, search/doc/2406.pdf)

Reducing Alkaloids: Storing

4. Storing for a long time lowers alkaloids. This includes hay and silage with comfrey in it. Also dried leaves and roots sold in bulk by the pound or in pill form.

"According to Danninger et al. (1983), in some species (Symphytum asperum= Rough/Prickly Comfrey), relatively long storage may lead to a reduction in the alkaloid content, presumably because enzymes are released during drying."

"Candrian et al. (1984b) studied the stability of PAs in hay and silage containing various amounts of Senecio alpinus (a plant high in alkaloids). The PA content of hay remained constant for several months, but the PAs in silage were mainly degraded. However, the degradation of PAs was much less complete in the lower concentration range."

(The above 2 paragraphs are from the World Health Organization, International Programme on Chemical Safety, Environmental Health Criteria 80, Pyrrolizidine Alkaloids, ehc/ehc/ehc080.htm)

Reducing Alkaloids: Cold

5. Time of harvest and climate affect alkaloid content. Cold winters reduce alkaloid levels.

"Leaves for medicinal use should be harvested during blooming due to lower alkaloid content."
(The Medicinal Herb Gardens at Ohio Northern University, garden/node/325)

"Some comfreys are more toxic than others. Russian comfrey (Symphytum x uplandicum) is one of the worst. And there's more hepatotoxic PAs in comfreys that are grown without a real winter, eg. in California."
(Henriettes Herbal, Henriette Kress,

Contact your health care specialist about comfrey and you.

Comfrey and Healing
Comfrey and Broken Bones
Comfrey Soap
Comfrey: Animals & Health
Comfrey Safety: Overview
Comfrey Safety: Processing
Comfrey Safety: Research
Comfrey: Need Studies

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