Herbal Monograph
Comfrey
Symphytum officinale L.
Boraginaceae
Potent topical vulnerary and anti-inflammatory for musculoskeletal injuries —...
Overview
Plant Description
Robust, coarse, clump-forming perennial herb, 30-120 cm tall, with a stout, erect, branching, angular stem that is winged (decurrent leaf bases) and densely covered in stiff, bristly hairs. Basal leaves large, up to 25-40 cm long and 10-15 cm wide, ovate-lanceolate, with a distinctly decurrent petiole that forms wings along the stem; upper leaves sessile and strongly decurrent. All leaves are covered on both surfaces with rough, bristly trichomes giving a characteristic sandpaper-like texture. Root system consists of a thick, fleshy, branching taproot with a black to dark brown exterior and white, mucilaginous interior; roots are extremely tenacious and regenerative — even small root fragments can produce new plants. Flowers are borne in terminal, scorpioid (coiled) cymes that unfurl as blooms open, a characteristic inflorescence of the Boraginaceae. Individual flowers are tubular-campanulate (bell-shaped), 12-18 mm long, nodding, with five fused petals, typically purple-violet, pink, or cream-white depending on variety. Fruits consist of four smooth, shiny, dark brown to black nutlets (schizocarps) at the base of the persistent calyx.
Habitat
Prefers moist to wet, fertile soils in partial shade to full sun. Naturally occurs along riverbanks, stream margins, ditches, moist meadows, damp roadsides, and in fenland habitats. Thrives in heavy clay soils with high moisture content. Tolerant of periodic flooding. pH tolerance is broad (5.0-8.0) but performs best in slightly alkaline to neutral soils. Once established, extremely difficult to eradicate due to deep, regenerative root system — any root fragment left in soil will produce a new plant.
Distribution
Native to Europe and western Asia, from the British Isles and Scandinavia south to the Mediterranean and east through the Caucasus to western Siberia. Widely naturalized in North America (particularly the northeastern United States and Pacific Northwest), parts of South America, southern Africa, Australia, and New Zealand. Commonly cultivated in temperate regions worldwide as a medicinal, compost, and fodder plant. Major commercial cultivation for pharmaceutical use occurs in Germany, Hungary, and eastern Europe.
Parts Used
Root (Symphyti radix)
Preferred: Dried root for ointment/cream preparations; fresh root poultice for traditional external application. All uses TOPICAL ONLY.
The root is the primary medicinal part recognized in the Commission E monograph, the EMA/HMPC monograph, ESCOP, and the European Pharmacopoeia. Contains the highest concentrations of allantoin (0.6-4.7%), mucilage polysaccharides (up to 29%), and rosmarinic acid, but also contains pyrrolizidine alkaloids (0.02-0.07% in S. officinale roots, higher in other species). APPROVED FOR EXTERNAL USE ONLY. The EMA monograph specifies 'Symphyti radix' — the dried, whole or cut root of Symphytum officinale L. The thick, fleshy root with its mucilaginous, white interior is the basis of most commercial comfrey preparations (Kytta-Salbe and similar products).
Leaf (Symphyti folium)
Preferred: Fresh leaf poultice (traditional); dried leaf for external wash or compress. All uses TOPICAL ONLY.
Leaves contain lower concentrations of allantoin and pyrrolizidine alkaloids compared to the root, though PA levels vary significantly with growing conditions and are not negligible. Leaves are used in folk tradition as fresh poultices applied directly to bruises, sprains, and swellings. Some commercial preparations use leaf extracts. The EMA monograph covers root only; leaves are not included in the official monograph. AHPA classifies both root and leaf as external use only. Historical internal use of comfrey leaf tea (as a demulcent for coughs and gastrointestinal inflammation) is now CONTRAINDICATED due to PA content.
Key Constituents
Pyrrolizidine alkaloids (PAs)
SAFETY-CRITICAL CONSTITUENTS — PAs are NOT therapeutically beneficial. They are the primary safety concern for all comfrey products. PAs are hepatotoxic, potentially genotoxic, and possibly carcinogenic. The 1,2-unsaturated PAs undergo hepatic bioactivation to reactive pyrrolic intermediates that cause sinusoidal obstruction syndrome (hepatic veno-occlusive disease — VOD), hepatocyte necrosis, and DNA cross-linking. IARC has classified certain PAs (lasiocarpine, riddelliine) as Group 2B (possibly carcinogenic to humans). The German BfArM limits topical PA exposure to a maximum of 100 micrograms unsaturated PAs per day, for no more than 4-6 weeks per year. Modern pharmaceutical comfrey preparations (e.g., Kytta-Salbe) use manufacturing processes to reduce or remove PA content. All internal use is contraindicated due to first-pass hepatic metabolism maximizing PA activation.
Purine derivatives
Allantoin is the primary therapeutically active cell-proliferant compound. It stimulates fibroblast proliferation, promotes granulation tissue formation, and accelerates epithelial regeneration. These actions underpin comfrey's traditional reputation as a bone-knitting and wound-healing herb. Commission E acknowledged comfrey's 'promotion of callus formation' as a documented action. Allantoin is also used as a standalone ingredient in many commercial wound-care and skin-care products outside of herbal medicine.
Phenolic acids and polyphenols
The phenolic acid fraction — particularly rosmarinic acid and caffeic acid oligomers — is the primary driver of comfrey's anti-inflammatory activity. Rosmarinic acid inhibits multiple inflammatory pathways including complement activation, prostaglandin biosynthesis, and NF-kB signaling. This anti-inflammatory action complements the cell-proliferant activity of allantoin, providing a dual mechanism for wound healing: reducing inflammation while simultaneously promoting tissue repair.
Mucilage polysaccharides
The high mucilage content provides significant demulcent and emollient properties to topical preparations. The mucilage creates a protective, moisture-retaining film over wounds and inflamed skin, which supports the wound-healing environment and enhances the delivery and activity of allantoin and rosmarinic acid. This accounts for the superior wound-healing properties of fresh root poultices compared to dry extracts.
Triterpene saponins and sterols
Minor contribution to anti-inflammatory activity. Not considered primary drivers of comfrey's therapeutic effects.
Other constituents
Tannins provide astringent and hemostatic properties that complement the vulnerary action. Silicic acid may contribute to connective tissue and bone support. These constituents provide ancillary therapeutic effects in the context of topical wound healing.
Herbal Actions
Comfrey's most established and historically important action. Allantoin stimulates cell division in fibroblasts, promotes granulation tissue formation, and accelerates epithelialization. Commission E recognized comfrey's 'promotion of callus formation' as a documented pharmacological action. The vulnerary effect is the basis for the traditional name 'knitbone' and the long history of use for fracture healing. IMPORTANT: The cell-proliferant action means comfrey should NOT be applied to deep, puncture, or heavily infected wounds, as it can cause the surface to heal over a pocket of infection (premature wound closure). EXTERNAL USE ONLY.
[1, 2, 4, 14]Reduces inflammation
Demonstrated in clinical trials and attributed primarily to rosmarinic acid and caffeic acid oligomers. Rosmarinic acid inhibits complement activation, prostaglandin synthesis, and NF-kB signaling. Clinical trials of topical comfrey root extract ointment demonstrated anti-inflammatory efficacy comparable to diclofenac gel in ankle sprains. A Symphytum officinale root extract was shown to affect two distinct steps of NF-kB signaling. EXTERNAL USE ONLY.
[1, 2, 10, 16]The exceptionally high mucilage content (up to 29% of dried root) provides significant emollient and protective properties when applied topically. Creates a soothing, moisture-retaining film over irritated or wounded skin. This property enhances the wound-healing environment and the delivery of allantoin and rosmarinic acid.
[4, 5]Clinical trials have demonstrated significant pain reduction with topical comfrey preparations in ankle sprains, knee osteoarthritis, and back pain. The analgesic effect is likely mediated through the anti-inflammatory activity (rosmarinic acid reducing prostaglandin-mediated pain signaling) rather than a direct analgesic mechanism. EXTERNAL USE ONLY.
[10, 12, 13]Therapeutic Indications
Musculoskeletal System
Ankle sprains and distortions (topical)
Commission E approved indication (bruises, sprains, strains — external use). Multiple RCTs support this indication. Koll et al. (2004): RCT of 142 patients showed comfrey root extract ointment (Kytta-Salbe f) was significantly superior to placebo for pain reduction (p<0.0001) and ankle edema reduction (p=0.0001). Predel et al. (2005): observer-blind RCT of 164 patients demonstrated comfrey ointment was non-inferior to diclofenac 1% gel for ankle distortions, with some outcome measures favoring comfrey. D'Anchise et al. (2007) confirmed non-inferiority to diclofenac gel. TOPICAL APPLICATION ONLY — apply ointment/cream to intact skin over the injured area 2-4 times daily.
[1, 9, 10, 11]Bruises and contusions (topical)
Commission E approved indication. EMA traditional use monograph: 'for the relief of minor sprains and bruises.' The anti-inflammatory and cell-proliferant actions promote resolution of bruising and associated pain and swelling. Apply topical preparations to intact skin over the bruised area. EXTERNAL USE ONLY.
[1, 2]Osteoarthritis of the knee (topical)
Grube et al. (2007): double-blind, randomized, placebo-controlled trial of 220 patients with painful knee OA found that comfrey root extract ointment (6g applied 3 times daily for 3 weeks) reduced VAS pain scores by 54.7% vs 10.7% in placebo group (difference 41.5 mm, p<0.001), with significant improvements in knee mobility (WOMAC) and quality of life. Giannetti et al. (2010): RCT confirmed benefit of comfrey-tannic acid cream blend for knee OA. ESCOP includes osteoarthritis among indications. TOPICAL APPLICATION ONLY.
[3, 12, 13]Acute upper and lower back pain (topical)
Giannetti et al. (2010): multicentre RCT of 379 patients with acute upper or low back pain demonstrated superiority of topical comfrey root extract plus methyl nicotinate over placebo. Staiger (2012) clinical overview confirmed evidence of benefit for back pain. TOPICAL APPLICATION ONLY.
[13, 14]Epicondylitis, tendovaginitis, and periarthritis (topical)
ESCOP monograph lists these conditions among indications supported by clinical experience. Anti-inflammatory and analgesic properties provide rationale for use in tendon and joint inflammation. Clinical evidence is limited compared to ankle sprain and knee OA studies. TOPICAL APPLICATION ONLY.
[3, 14]Skin / Integumentary
Minor wounds, abrasions, and superficial lacerations (topical)
Traditional vulnerary use supported by allantoin's cell-proliferant activity. Commission E recognized wound-healing as a traditional action. IMPORTANT CAUTION: Comfrey's powerful cell-proliferant action means it must NOT be applied to deep wounds, puncture wounds, or heavily infected wounds — premature surface closure can trap infection underneath. Apply only to minor, clean, superficial wounds. Do NOT apply to broken skin where significant PA absorption could occur. EXTERNAL USE ONLY.
[1, 2, 4]Fracture healing support (topical, adjunctive)
The traditional use that gives comfrey its name 'knitbone.' Commission E acknowledged 'promotion of callus formation' as a documented action. Allantoin stimulates osteoblast proliferation and may support fracture callus formation when applied topically over the fracture site (through intact skin). Clinical evidence is limited to traditional reports and preliminary studies. This application is adjunctive to standard orthopedic management, not a replacement. TOPICAL APPLICATION ONLY.
[1, 4, 7]Energetics
Temperature
cool
Moisture
moist
Taste
Tissue States
hot/excitation, dry/atrophy, wind/tension
Comfrey is cooling and moistening in Western energetic assessment. Its copious mucilage gives a distinctly slimy, moistening quality that soothes hot, dry, irritated tissues — the hallmark of a demulcent herb. The cooling nature addresses inflammatory heat in injured tissues, while the moistening quality supports tissue repair in conditions of dryness and atrophy. The mild astringency from tannins adds a subtle toning dimension. Indicated for hot, dry, inflamed tissue states — the opposite of the cold, damp, congestive picture where warming stimulants are needed. Hoffmann describes comfrey as having a particular affinity for bone, connective tissue, and mucous membranes. In historical Western energetics (pre-PA safety concerns), comfrey was considered a supreme tissue healer for its ability to 'knit together' damaged tissues through its cooling, moistening, nourishing, and cell-proliferating properties.
Traditional Uses
European traditional herbalism (historical — MANY USES NOW CONTRAINDICATED)
- External poultice of root or leaf for fractures, sprains, and dislocations ('knitbone')
- External application for bruises, swellings, and contusions
- External root poultice for wound healing and ulcers
- HISTORICAL internal use as demulcent tea for gastric ulcers and gastritis (NOW CONTRAINDICATED due to PA content)
- HISTORICAL internal use for coughs, bronchitis, and pleurisy (NOW CONTRAINDICATED)
- HISTORICAL internal use for internal hemorrhage and bleeding (NOW CONTRAINDICATED)
- HISTORICAL internal leaf decoction as a general tonic (NOW CONTRAINDICATED)
"Hoffmann (2003): 'Comfrey is a powerful healing agent for wounds, sprains, fractures, and bruises. The root contains allantoin, which is responsible for its remarkable ability to promote tissue repair. Comfrey is a potent cell proliferant, causing rapid growth of cells. The plant has a long history of use as a bone-knitting herb, hence the name knitbone... However, the presence of pyrrolizidine alkaloids in comfrey limits its use to external applications only. Internal use cannot be recommended.' Hoffmann explicitly recommends EXTERNAL USE ONLY due to PA concerns, while acknowledging the historical internal uses."
[4]
Ancient Greek and Roman medicine (historical)
- Treatment of fractures and broken bones (external poultice)
- Wound healing and hemorrhage control
- Respiratory complaints (internal — NOW CONTRAINDICATED)
"The genus name Symphytum derives from the Greek 'sympho' (to make grow together) and 'phyton' (plant), directly referencing the bone-knitting use. Dioscorides (De Materia Medica, 1st century CE) prescribed comfrey root poultices for fractures, wounds, and respiratory ailments. Pliny the Elder (Naturalis Historia) described how boiling comfrey roots in water produced a sticky paste so adhesive it could glue pieces of meat together — an observation reflecting the high mucilage content."
[14]
English herbalism (16th-17th century — historical)
- External application for bone fractures and tissue repair
- HISTORICAL internal use for wounds, hemorrhage, and respiratory complaints (NOW CONTRAINDICATED)
- Poultice for gout and joint inflammation
"Nicholas Culpeper (The English Physitian, 1652): 'The root boiled in water or wine, and the decoction drank, helpeth all inward hurts, bruises, wounds, and ulcers of the lungs, and causeth the phlegm that oppresseth them to be easily spit forth. It is said to be so powerful to consolidate and knit together that if they be boyled with dissevered pieces of flesh in a pot, it will join them together again.' John Gerard (The Herball, 1597): 'The slimie substance of the roote made in a possett of ale' was recommended for back pains. NOTE: The internal uses described by Culpeper and Gerard are NOW CONTRAINDICATED due to pyrrolizidine alkaloid hepatotoxicity."
[14]
German phytotherapy (Commission E / ESCOP / EMA)
- External: Bruises, sprains, strains (Commission E approved)
- External: Blunt injuries (Commission E approved)
- External: Osteoarthritis, epicondylitis, tendovaginitis (ESCOP)
- External: Relief of symptoms of minor sprains and bruises (EMA traditional use)
"Commission E (1990) approved comfrey root for external use in bruises, pulled muscles and ligaments, and sprains, acknowledging anti-inflammatory, antimitotic, and callus-promoting actions. ESCOP (2009) expanded indications to include osteoarthritis, epicondylitis, tendovaginitis, and periarthritis. The EMA/HMPC (2015) established a traditional use monograph for 'the relief of symptoms of minor sprains and bruises,' specifying external use for a maximum duration of 10 days."
British Herbal Pharmacopoeia
- External: Fractures, bruises, sprains
- HISTORICAL internal: Gastric and duodenal ulcers, colitis (NOW CONTRAINDICATED)
"BHP (1983) listed comfrey root for fractures, bruises, and sprains (external) and historically for gastrointestinal conditions (internal). Subsequent editions and the modern British understanding restrict use to external application only due to PA safety concerns."
[7]
Modern Research
Topical treatment of ankle sprains — placebo-controlled RCT
Multicenter, randomized, double-blind, placebo-controlled trial of comfrey root extract ointment for acute ankle sprains.
Findings: Koll et al. (2004) randomized 142 patients with acute unilateral ankle sprains to comfrey root extract ointment (Kytta-Salbe f) or placebo, applied 4 times daily for 8 days. The comfrey group showed significantly greater reduction in pain on active movement (p<0.0001), reduction in ankle edema (p=0.0001), and improvement in ankle mobility compared to placebo. Global efficacy assessments by both investigators and patients significantly favored the active treatment.
Limitations: Relatively short treatment duration (8 days). Single commercial preparation tested (Kytta-Salbe f). Results may not be generalizable to all comfrey products. Moderate sample size.
[9]
Comfrey vs. diclofenac gel for ankle sprains — active comparator RCT
Observer-blind, randomized, multicenter trial comparing comfrey root extract ointment to diclofenac 1% gel for acute ankle distortions.
Findings: Predel et al. (2005) randomized 164 outpatients with acute unilateral ankle sprains to comfrey root extract ointment or diclofenac 1% gel, applied 4 times daily for 7 days. Comfrey ointment was demonstrated to be non-inferior to diclofenac gel. The 95% confidence interval for the treatment difference was completely above the pre-defined non-inferiority margin. Some secondary endpoints suggested superiority of the comfrey preparation. D'Anchise et al. (2007) independently confirmed non-inferiority of comfrey to diclofenac gel in a subsequent trial.
Limitations: Observer-blind rather than fully double-blind (ointment vs. gel formulations are distinguishable). Non-inferiority design limits conclusions about superiority. Both trials used the same proprietary PA-reduced preparation.
Knee osteoarthritis — placebo-controlled RCT
Double-blind, randomized, placebo-controlled trial of comfrey root extract ointment for painful osteoarthritis of the knee.
Findings: Grube et al. (2007) randomized 220 patients with painful knee OA to comfrey root extract ointment (6g applied 3 times daily) or placebo for 3 weeks. The comfrey group showed a 54.7% reduction in VAS pain score compared to 10.7% in the placebo group — a highly significant difference of 41.5 mm (p<0.001). Significant improvements were also observed in WOMAC total scores, knee mobility, and quality of life. The magnitude of the treatment effect was clinically meaningful.
Limitations: 3-week treatment duration may not reflect long-term efficacy or safety for a chronic condition. Long-term topical PA exposure with repeated use requires monitoring. Proprietary PA-reduced preparation used.
[12]
Back pain — placebo-controlled RCT
Multicenter, double-blind, randomized, placebo-controlled trial of topical comfrey root extract combination for acute back pain.
Findings: Giannetti et al. (2010) randomized 379 patients with acute upper or lower back pain to a topical combination of 35% comfrey root extract plus 1.2% methyl nicotinate versus placebo. The active treatment showed significant superiority over placebo in reducing pain and improving back mobility. The combination preparation was well tolerated with no serious adverse effects reported.
Limitations: The preparation included methyl nicotinate (a rubefacient) in addition to comfrey extract, making it difficult to attribute effects solely to comfrey. Acute back pain only — chronic back pain not studied.
[13]
Pyrrolizidine alkaloid hepatotoxicity — toxicology review
Review of PA toxicity mechanisms, documented hepatic veno-occlusive disease cases, genotoxicity, and carcinogenicity data for comfrey.
Findings: Multiple case reports document hepatic veno-occlusive disease (sinusoidal obstruction syndrome) following internal comfrey use. A systematic review through 2017 identified 8 documented cases of adverse hepatic reactions attributable to comfrey ingestion, including at least one fatality (a 23-year-old male who consumed comfrey preparations). PAs are bioactivated hepatically via CYP3A4 to reactive dehydro-pyrrolizidine metabolites that form DNA and protein adducts. Animal studies confirm hepatotoxicity, genotoxicity, and carcinogenicity. The NTP (National Toxicology Program) found 'clear evidence of carcinogenic activity' of comfrey in rats and mice (liver hemangiosarcoma and hepatocellular adenoma/carcinoma). IARC has classified certain PAs as Group 2B (possibly carcinogenic to humans).
Limitations: Human case reports are limited in number and often involve confounding factors (concurrent medications, underlying liver disease, uncertain species identification, or unclear dosing). Animal carcinogenicity data involved high-dose oral exposure over prolonged periods. Dermal PA absorption is minimal (lycopsamine is poorly absorbed through human skin), supporting the relative safety of topical use.
Dermal absorption of pyrrolizidine alkaloids — safety of topical use
Investigation of whether PAs in topical comfrey preparations are absorbed through intact human skin in clinically relevant amounts.
Findings: Schenk et al. (2020) investigated dermal absorption of the PA lycopsamine (the predominant PA in S. officinale) through human skin using Franz diffusion cell methodology. The study found that lycopsamine is poorly absorbed through intact human skin — permeation was minimal and well below levels of toxicological concern. This supports the safety rationale for topical comfrey use with PA-containing preparations, provided skin is intact and application duration is limited. The authors concluded that the risk from topical exposure to PAs in comfrey cream preparations applied to intact skin is very low.
Limitations: In vitro study using excised human skin. Does not account for compromised skin barrier (wounds, abrasions, eczema), which could increase PA absorption. Only lycopsamine was tested; other PAs may have different permeation characteristics.
[15]
Anti-inflammatory mechanism — NF-kB pathway
Investigation of the anti-inflammatory mechanism of Symphytum officinale root extract through NF-kB signaling modulation.
Findings: Trifan et al. (2019) demonstrated that a S. officinale root extract exerts anti-inflammatory properties by affecting two distinct steps of NF-kB signaling: inhibition of IKK-beta phosphorylation (upstream) and inhibition of NF-kB p65 nuclear translocation (downstream). Rosmarinic acid and caffeic acid derivatives were identified as the primary contributors to this activity. The extract also reduced pro-inflammatory cytokine release (TNF-alpha, IL-6, IL-1beta) in stimulated macrophages.
Limitations: In vitro study in cell culture. Concentrations tested may not reflect achievable tissue concentrations from topical application. Clinical relevance needs confirmation.
[16]
Clinical overview and evidence synthesis
Comprehensive clinical review of comfrey's efficacy and safety across all studied indications.
Findings: Staiger (2012) published a clinical overview synthesizing evidence from multiple RCTs. Individual clinical trials showed evidence of benefit for ankle distortion (sprains), back pain, abrasion wounds, and osteoarthritis. The review confirmed that topical preparations of comfrey root extract are effective for the treatment of pain, inflammation, and swelling in musculoskeletal conditions. The PA safety concern is adequately managed by restricting use to topical application of standardized, PA-reduced preparations, applied to intact skin for limited durations.
Limitations: Narrative review rather than systematic review/meta-analysis. All major RCTs used the same commercial preparation (Kytta-Salbe f or variants), limiting generalizability to other comfrey products. Industry funding for several included studies.
[14]
Preparations & Dosage
topical
Strength: Commercial preparations: typically 10-35% comfrey root extract in ointment base. Extemporaneous: 1:5 infused oil (dried root:carrier oil by weight).
Ointment/cream: Commercial standardized preparations (e.g., Kytta-Salbe f containing 35% comfrey root extract) are preferred due to controlled PA content. Apply a generous layer (approximately 6g per application for knee OA; 3-4g for ankle sprains) to the affected area 2-4 times daily. Massage gently into intact skin. Cover with a clean bandage if desired. For extemporaneous preparations: infuse comfrey root in a carrier oil (olive oil, coconut oil) by gentle heat method (40-50C for 4-8 hours) or cold maceration (4-6 weeks), strain, and combine with beeswax (approximately 1 part beeswax to 4 parts infused oil) to form an ointment.
Apply to affected area 2-4 times daily. Commercial preparations typically applied in 3-6g amounts per application.
2-4 times daily
Maximum 10 days per treatment episode (EMA recommendation). German BfArM limits total annual topical PA exposure to 4-6 weeks per year. Do not exceed these limits.
Topical use may be appropriate for children aged 3 years and older under practitioner supervision. Limit duration and frequency. Not recommended for children under 3 years.
CRITICAL: Topical application to INTACT SKIN ONLY. Do NOT apply to open wounds, broken skin, or large abrasion areas where dermal absorption of PAs could be significant. Duration limits must be observed. Standardized, PA-reduced commercial preparations are strongly preferred over extemporaneous preparations, as PA content in crude comfrey material is variable and potentially high. Wash hands after application.
Poultice
Strength: Fresh root grated directly, or dried powdered root mixed with warm water to paste consistency
Traditional fresh root poultice: Grate or pulp fresh comfrey root to produce a mucilaginous paste. Alternatively, mix dried, powdered comfrey root with warm water to form a thick paste. Spread the paste 3-5 mm thick on a clean cloth, apply the cloth paste-side-down to the affected area, and secure with a bandage. Leave in place for 1-4 hours. Replace as needed. Fresh leaf poultice: Bruise or lightly blanch fresh comfrey leaves and apply directly to the affected area; secure with a bandage.
Sufficient quantity to cover the affected area. Apply 1-2 times daily.
1-2 times daily
Use for a maximum of 10 consecutive days per episode. Total annual use should not exceed 4-6 weeks.
May be used for children aged 3 years and older under practitioner supervision. Limit duration.
The traditional poultice is the oldest form of comfrey application. Fresh root poultice delivers maximum mucilage and allantoin content. APPLY TO INTACT SKIN ONLY — do not apply over open wounds or broken skin. PA content in fresh root is uncontrolled; observe strict duration limits. Despite traditional historical use of comfrey poultices directly on open wounds, modern safety guidelines restrict application to intact skin only due to PA absorption risk.
compress
Strength: 50-100g dried root per 500 mL water (decoction)
Prepare a strong decoction by simmering 50-100g dried comfrey root in 500 mL water for 10-15 minutes. Strain. Soak a clean cloth in the warm decoction, wring out excess, and apply to the affected area. Reapply when the cloth cools. Continue for 20-30 minutes per session.
Apply warm compresses to affected area for 20-30 minutes, 2-3 times daily
2-3 times daily
Maximum 10 days per treatment episode
May be used for children aged 3 years and older with appropriate temperature precautions
Warm compresses provide the soothing demulcent quality of the mucilage along with anti-inflammatory and cell-proliferant activity. APPLY OVER INTACT SKIN ONLY. This preparation delivers PA-containing liquid to the skin; observe duration limits strictly.
[4]
Safety & Interactions
Class 2b
Not to be used during lactation (AHPA Botanical Safety Handbook)
Contraindications
ALL internal use of comfrey is CONTRAINDICATED. Comfrey contains 1,2-unsaturated pyrrolizidine alkaloids (PAs) that are hepatotoxic, potentially genotoxic, and possibly carcinogenic. PAs are bioactivated by hepatic CYP3A4 to reactive dehydro-pyrrolizidine metabolites that cause sinusoidal obstruction syndrome (hepatic veno-occlusive disease), hepatocyte necrosis, and DNA adduct formation. Documented case reports include hepatic VOD, liver failure, and at least one fatality following comfrey ingestion. The NTP found 'clear evidence of carcinogenic activity' in rodents. Internal use is BANNED or restricted by regulatory agencies worldwide: FDA (USA, 2001), TGA (Australia, 2001), EMA (EU), BfArM (Germany), and Health Canada. AHPA classification: Class 2b (not to be used during pregnancy) and 2c (not to be used while nursing), with the overriding recommendation that comfrey is for external use only.
Do NOT apply comfrey preparations to open wounds, broken skin, deep wounds, or extensive abrasion areas. Although dermal absorption of PAs through intact skin is minimal (Schenk et al., 2020), compromised skin barrier significantly increases the potential for systemic PA absorption. Furthermore, comfrey's powerful cell-proliferant action (allantoin) can cause premature wound surface closure, trapping infection underneath in deep or contaminated wounds. The EMA monograph specifies 'cutaneous use on intact skin only.'
AHPA Class 2b — not to be used during pregnancy. PA exposure during pregnancy poses potential hepatotoxic and genotoxic risk to the developing fetus. No adequate human safety data. Even topical use during pregnancy is not recommended as a precaution due to the theoretical (though likely very low) risk of transdermal PA absorption. The EMA monograph explicitly contraindicates use during pregnancy.
AHPA Class 2c — not to be used during nursing. PAs and their metabolites may be transferred via breast milk, posing a hepatotoxic risk to the nursing infant whose hepatic detoxification capacity is immature. Even topical use is not recommended during breastfeeding as a precaution. The EMA monograph contraindicates use during lactation.
Patients with hepatic impairment, liver disease, or a history of hepatic veno-occlusive disease must not use comfrey in any form (internal or topical). Compromised hepatic function reduces the ability to detoxify any PAs that may be absorbed, increasing vulnerability to hepatotoxic effects.
The EMA monograph does not recommend use in children under 3 years. Immature hepatic function in young children increases vulnerability to any absorbed PAs. The risk-benefit assessment does not support use in this age group.
Drug Interactions
| Drug / Class | Severity | Mechanism |
|---|---|---|
| Hepatotoxic drugs (Hepatotoxic agents (acetaminophen/paracetamol, certain statins, methotrexate, isoniazid, etc.)) | theoretical | Any PAs absorbed through the skin could theoretically compound hepatotoxic burden in patients taking other hepatotoxic medications. PAs are metabolized by CYP3A4; concurrent use with drugs that inhibit CYP3A4 could theoretically alter PA metabolism. |
| CYP3A4 inhibitors (CYP3A4 inhibitors (ketoconazole, erythromycin, grapefruit juice, etc.)) | theoretical | CYP3A4 is responsible for the bioactivation of PAs to toxic pyrrolic metabolites. Inhibition of CYP3A4 could theoretically reduce PA bioactivation. However, this interaction is only relevant if PAs reach the liver (i.e., with internal use or significant dermal absorption through compromised skin). |
Pregnancy & Lactation
Pregnancy
unsafe
Lactation
unsafe
AHPA Class 2b (not to be used during pregnancy) and 2c (not to be used during nursing). The EMA monograph explicitly contraindicates use during pregnancy and lactation. Pyrrolizidine alkaloids are potentially teratogenic and genotoxic. PAs and their metabolites may cross the placenta and may be transferred via breast milk. Even topical use is not recommended during pregnancy or lactation as a precaution, despite the low dermal absorption of PAs through intact skin. The immature hepatic enzyme systems of the fetus and nursing infant increase vulnerability to any PA exposure. No adequate human safety data exist to support use during pregnancy or lactation.
Adverse Effects
References
Monograph Sources
- [1] Blumenthal, M., Busse, W.R., Goldberg, A., et al.. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines — Symphyti radix (Comfrey root). American Botanical Council / Integrative Medicine Communications (1998) . ISBN: 978-0965555500
- [2] Committee on Herbal Medicinal Products (HMPC). European Union herbal monograph on Symphytum officinale L., radix. European Medicines Agency (2015)
- [3] ESCOP (European Scientific Cooperative on Phytotherapy). ESCOP Monographs: The Scientific Foundation for Herbal Medicinal Products — Symphyti radix (Comfrey root). ESCOP / Thieme (2009) . ISBN: 978-1901964264
- [4] Hoffmann, D.. Medical Herbalism: The Science and Practice of Herbal Medicine. Healing Arts Press (2003) . ISBN: 978-0892817498
- [5] Mills, S., Bone, K.. Principles and Practice of Phytotherapy: Modern Herbal Medicine (2nd edition). Churchill Livingstone / Elsevier (2013) . ISBN: 978-0443069925
- [6] Gardner, Z., McGuffin, M. (eds.). American Herbal Products Association's Botanical Safety Handbook (2nd edition). CRC Press (2013) . ISBN: 978-1466516946
- [7] British Herbal Medicine Association. British Herbal Pharmacopoeia. BHMA (1983)
- [8] Brinker, F.. Herbal Contraindications and Drug Interactions (4th edition). Eclectic Medical Publications (2010) . ISBN: 978-1888483147
Clinical Studies
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- [10] Predel, H.G., Giannetti, B., Koll, R., et al.. Efficacy of a comfrey root extract ointment in comparison to a diclofenac gel in the treatment of ankle distortions: results of an observer-blind, randomized, multicenter study. Phytomedicine (2005) ; 12 : 707-714 . DOI: 10.1016/j.phymed.2005.06.001 . PMID: 16323288
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- [12] Grube, B., Grunwald, J., Krug, L., Staiger, C.. 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 (2007) ; 14 : 2-10 . DOI: 10.1016/j.phymed.2006.11.005 . PMID: 17169543
- [13] Giannetti, B.M., Staiger, C., Bulitta, M., Predel, H.G.. Efficacy and safety of comfrey root extract ointment in the treatment of acute upper or lower back pain: results of a double-blind, randomised, placebo controlled, multicentre trial. British Journal of Sports Medicine (2010) ; 44 : 637-641 . DOI: 10.1136/bjsm.2009.058677 . PMID: 19460762
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- [15] Schenk, A., Siewert, B., Toff, S., Drewe, J.. Safety of medicinal comfrey cream preparations (Symphytum officinale s.l.): The pyrrolizidine alkaloid lycopsamine is poorly absorbed through human skin. Regulatory Toxicology and Pharmacology (2020) ; 117 : 104780 . DOI: 10.1016/j.yrtph.2020.104780 . PMID: 32941922
- [16] Trifan, A., Opitz, S.E.W., Joray, M.B., et al.. A Symphytum officinale Root Extract Exerts Anti-inflammatory Properties by Affecting Two Distinct Steps of NF-kB Signaling. Frontiers in Pharmacology (2019) ; 10 : 289 . DOI: 10.3389/fphar.2019.00289 . PMID: 30971929
- [17] Yeong, M.L., Swinburn, B., Kennedy, M., Nicholson, G.. Hepatic veno-occlusive disease associated with comfrey ingestion. Journal of Gastroenterology and Hepatology (1990) ; 5 : 513-516 . DOI: 10.1111/j.1440-1746.1990.tb01827.x . PMID: 2103401
- [18] National Toxicology Program (NTP). NTP Technical Report on the Toxicology and Carcinogenesis Studies of Comfrey (Symphytum officinale) in F344/N Rats and B6C3F1 Mice. National Institutes of Health, U.S. Department of Health and Human Services (2001)
Pharmacopeias & Reviews
- [19] European Pharmacopoeia Commission. European Pharmacopoeia — Symphyti radix (Comfrey root). Council of Europe / EDQM (2023)
Last updated: 2026-03-02 | Status: review
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