Comfrey
Comfrey (Symphytum officinale)
Plant family
Borageinaceae
Other significant names
Knitbone
Boneset
Parts used
Folia (foliage)
Historically, root (radix) was used
Typical forms of prescription
Poultice
Infused oil
Topicals
Tincture
Symphytum officinale (Comfrey) - Clinical Snapshot
Primary Actions
Vulnerary
Demulcent
Anti-inflammatory
Primary Indications
Broken bones (When set in place)
Sprains
Strains
⚠️ Cautions / Safety ⚠️
Contains pyrrolizidine alkaloids (PAs)
Internal use not recommended for:
Young children
Long-term use for anyone
Elderly
Pregnancy
Liver or kidney conditions
Suspected liver issues
Symphytum officinale
Phytochemistry and Pharmacology
Allantoin
Action: Cell-proliferative, wound-healing, anti-inflammatory.
Use: Allantoin stimulates the growth of new tissue and accelerates wound healing. It’s especially useful for bruises, sprains, fractures, and ulcers. This compound makes Comfrey a go-to herb for skin and bone repair, hence the traditional name “knitbone.”
Rosmarinic Acid
Action: Anti-inflammatory, antioxidant, antimicrobial.
Use: Rosmarinic acid supports tissue healing and reduces inflammation. It adds to Comfrey’s use in managing joint and muscle pain, inflamed skin, and wound recovery.
Pyrrolizidine Alkaloids (PAs)
Action: Anti-inflammatory (but potentially hepatotoxic).
Use: PAs contribute to Comfrey’s anti-inflammatory power but raise safety concerns due to their liver toxicity in high doses or long-term use. Modern use of Comfrey often focuses on topical application only or on PA-free internal extracts.
Mucilage
Action: Demulcent, soothing, anti-inflammatory.
Use: Mucilage soothes irritated tissues, especially in the respiratory and digestive systems. It helps protect damaged mucosa and is calming when applied to wounds or taken for throat irritation.
Traditional use
Comfrey, once revered as a panacea herb, was traditionally used for gastrointestinal ulcers, broken bones, and as a nutritious pot herb. Its reputation as "knitbone" reflects centuries of use for sprains, fractures, and tissue damage. It was also employed as an expectorant for chest complaints. However, many of its internal applications are no longer recommended due to concerns about liver toxicity from its pyrrolizidine alkaloids (PAs).
Clinical Description
Comfrey contains allantoin, a compound that stimulates cell proliferation and supports tissue repair. This makes it a powerful vulnerary herb, ideal for topical use on bruises, sprains, strains, and fractures—but only on unbroken skin. Its ability to speed up surface healing means it can seal in infection if used on open wounds or abscesses.
Topically, comfrey is applied as a poultice, infused oil, or salve to reduce inflammation and pain, support bone healing, and encourage muscle and ligament repair. Importantly, it should only be applied after fractures are properly set, as premature use may lead to incorrect bone knitting that requires re-breaking.
Due to its PA content, comfrey is no longer recommended for internal use, especially in vulnerable groups (children, pregnant people, those with liver issues). PA toxicity is cumulative, potentially causing gradual liver degeneration over time. Some modern preparations use PA-free extracts, though these are more common in regulated products.
Cultivation/Harvesting
Comfrey is a vigorous perennial, thriving in rich, moist soil with full sun to partial shade. Once established, it’s low-maintenance and can be cut several times a year. It’s often used as a green manure or compost activator due to its high nutrient content.
For medicinal use, Symphytum officinale is the species authorised for short-term internal use in regulated products, though this is rare.
Other species (e.g., S. x uplandicum) are commonly used externally.
PAs are highest in roots and young leaves. Harvest older leaves in summer during flowering for topical remedies.
Dry carefully or use fresh in oils and poultices.
Key Botanical Features of Comfrey (Symphytum officinale)
Growth
Type: Herbaceous perennial.
Size: 30–120 cm (1–4 feet) tall.
Stem: Erect, branched, angular, and covered with coarse hairs.
Leaves
Type: Alternate, simple.
Shape: Lanceolate (narrow and pointed) or ovate.
Size: 10–30 cm (4–12 inches) long.
Texture: Rough, hairy, and slightly wrinkled.
Colour: Dark green.
Flowers
Type: Drooping, tubular to bell-shaped, arranged in curved clusters (scorpiod cymes).
Colour: Purple, violet, pink, or white.
Size: 1–2 cm (0.4–0.8 inches) long.
Blooming Period: Late spring to summer.
Pollination: Primarily bee-pollinated.
Fruits & Seeds
Fruit Type: Small, nut-like schizocarps, breaking into four smooth, shiny nutlets.
Seed Dispersal: Gravity and water-assisted dispersal.
Roots
Type: Thick, black, and deeply tap-rooted with lateral rhizomes.
Function: Helps with nutrient accumulation and drought resistance.
Habitat & Growth Conditions
Climate: Prefers temperate regions.
Soil: Thrives in moist, fertile, well-drained soil.
Sunlight: Grows best in full sun to partial shade.
Distribution: Native to Europe and Asia, naturalised in North America; often found in meadows, riverbanks, and disturbed areas.
Sustainability/Conservation
An abundant common plant.
Sources
Bartram, T. (1998). Bartram’s Encyclopedia of Herbal Medicine. Constable.
Fisher, C. (2009). Materia Medica of Western Herbs, (2018 edition). Finchley Road, London. Aeon Books.
Hedley, C & Shaw, N. (2020). A herbal book of making and taking. Finchley Road, London. Aeon Books.
Hoffmann, D. (2003). Medical Herbalism: The Science and Practice of Herbal Medicine. Healing Arts Press.
McIntyre, A. (2019). The complete herbal tutor, revised and expanded edition. Finchley Road, London. Aeon Books.
Plants of the World Online | Kew Science. (n.d.). Plants of the World Online. https://powo.science.kew.org/
Disclaimer: This page is for educational purposes only. Consult a qualified medical herbalist before using herbs, especially during pregnancy, when trying to conceive, while breastfeeding, for medical conditions, or with children.
Read the full disclaimer → Medical Disclaimer.