Comfrey

Metadata

Approved Indications

German Commission E

• Positive monograph for EXTERNAL use only:
  • Bruises (contusions)
  • Strains (distortions)
  • Sprains
• Negative monograph for INTERNAL use: Prohibited due to pyrrolizidine alkaloid content
• Duration limit: Not longer than 4-6 weeks per year; not for children/adolescents under 18

ESCOP

External use for:

• Pain and swelling of muscles and joints
• Arthritis of joints
• Acute back pain
• Muscle strains, contusions, and sprains
• Epicondylitis (tennis elbow)
• Tenosynovitis (tendon sheath inflammation)
• Periarthritis

EMA/HMPC

• Restricts use to external application only and for short periods
• Duration limits enforced due to PA content even in topical products

Agreement/Disagreement Among Authorities

• Strong agreement: All authorities prohibit internal use; all recognize external use for sprains, strains, and bruises
• ESCOP is broadest: Includes arthritis, back pain, epicondylitis, tenosynovitis — reflecting the stronger clinical trial evidence accumulated since the Commission E monograph
• Duration limits vary: Commission E states max 4-6 weeks/year; some authorities are less specific
• PA thresholds: EMA has set limits on PA content in topical products; modern products must be PA-depleted

Conditions Treated

Primary (Evidence-Supported, Topical)

• Ankle sprains/distortions — strongest evidence (multiple RCTs, including vs. diclofenac)
• Knee osteoarthritis — large placebo-controlled RCT (Grube 2007)
• Acute back pain (upper and lower) — placebo-controlled RCT
• Muscle strains and contusions — supported by trials

Secondary (ESCOP-Recognized, Topical)

• Epicondylitis (tennis elbow)
• Tenosynovitis
• Periarthritis
• General myalgia

ABSOLUTELY NOT INDICATED

• Any internal/oral use — hepatotoxic, potentially carcinogenic pyrrolizidine alkaloids
• No internal preparations should ever be used, regardless of the PA content claimed

Mechanism of Action

Key Active Compounds

• Allantoin: Cell proliferant; promotes wound healing, tissue regeneration, and callus formation; 0.6-4.7% in root
• Rosmarinic acid: Anti-inflammatory (inhibits complement cascade and prostaglandin synthesis); antioxidant
• Mucopolysaccharides (mucilage): Provide emollient and anti-inflammatory effects; aid in skin penetration of other actives
• Choline: Precursor for phospholipid synthesis; supports cell membrane repair
• Tannins: Astringent, mild anti-inflammatory
• Pyrrolizidine alkaloids (PAs): TOXIC COMPOUNDS (not therapeutic) — including symphytine, echimidine, lycopsamine; responsible for hepatotoxicity

Pharmacological Mechanisms

1. Anti-inflammatory: Rosmarinic acid inhibits complement C3 convertase and reduces prostaglandin synthesis; comfrey root extract inhibits NF-kB signaling at two distinct steps [Source: Sowa et al., 2019]
2. Cell proliferation and tissue repair: Allantoin stimulates cell division and promotes granulation tissue formation (“knitbone” traditional name reflects this)
3. Analgesic: Mechanism not fully elucidated; likely combination of anti-inflammatory effect reduction of pain-generating mediators and direct soothing of irritated tissue
4. Anti-edema: Mucilage components reduce swelling at injury sites
5. Callus formation promotion: Commission E recognizes this specific action for bone healing support

Penetration and Bioavailability

Modern formulations (ointments, creams) are designed to optimize dermal penetration of allantoin and rosmarinic acid. The PA lycopsamine has been shown to be poorly absorbed through intact human skin [Source: Staiger et al., 2020], which is one basis for the acceptable safety profile of PA-depleted topical products.

Clinical Evidence Summary

Key Clinical Trials (Kytta-Salbe Program)

The German product Kytta-Salbe f (comfrey root fluid extract ointment, manufactured by Merck) has the most extensive clinical trial program of any comfrey product:

Ankle Sprains

Knee Osteoarthritis

This is an exceptionally large effect size for a topical treatment and represents some of the strongest evidence for any herbal topical product.

Back Pain

Blunt Injuries (Comprehensive)

Effect Sizes

• Knee OA: 54.7% pain reduction vs. 10.7% placebo — NNT estimated ~2 for clinically meaningful response
• Ankle sprains: Comfrey outperformed diclofenac gel — this is a notable finding given diclofenac’s well-established efficacy
• Back pain: Significant effect within 5 days

Alternative Comfrey Product: Traumaplant

• Traumaplant uses an extract from Symphytum x uplandicum (Russian comfrey hybrid) leaves
• Contains 10% comfrey leaf extract
• Marketed as pyrrolizidine alkaloid-free
• Also studied in clinical trials for sprains and blunt injuries
• Available in the US market (Terry Naturally brand)

European vs. US/Anglophone Consensus

Key insight: The US narrative around comfrey focuses almost exclusively on the PA toxicity risk (which is real for internal use), while overlooking the genuinely strong clinical trial evidence for PA-depleted topical preparations. This represents a case where legitimate safety concerns about one route of administration have unfairly discredited another.

Safety Profile

CRITICAL SAFETY WARNING: PYRROLIZIDINE ALKALOIDS (PAs)

Internal/oral use of comfrey in any form is ABSOLUTELY CONTRAINDICATED.

Pyrrolizidine alkaloids (symphytine, echimidine, lycopsamine, and others) in comfrey are:

• Hepatotoxic: Cause hepatic veno-occlusive disease (sinusoidal obstruction syndrome)
• Potentially carcinogenic: Classified as possibly carcinogenic in animal studies
• Genotoxic: Mutagenic in standard assays

Case reports of liver failure and death have been associated with internal comfrey use.

Contraindications (Topical Use)

• Pregnancy: Contraindicated (PAs have abortifacient effects; even low dermal absorption is a concern)
• Lactation: Contraindicated (alkaloids detected in breast milk in animal studies)
• Children/adolescents under 18: Commission E contraindicates
• Open wounds or damaged skin: PA absorption increases with compromised skin barrier
• Liver disease: Even topical use should be avoided in patients with pre-existing hepatic impairment
• Duration: Maximum 4-6 weeks per year of continuous use (Commission E)

Drug Interactions

• No significant drug interactions reported for topical use
• Internal use (which should never occur) would interact with hepatotoxic medications

Side Effects (Topical)

• Generally well-tolerated
• Occasional local skin irritation
• Allergic contact dermatitis (uncommon)
• Systemic PA exposure from topical use: Studies show that lycopsamine (the dominant PA in comfrey) is poorly absorbed through intact human skin. Modern PA-depleted products further minimize this risk. However, applying to large skin areas, broken skin, or for extended periods increases theoretical risk

Pregnancy and Lactation

• Pregnancy: CONTRAINDICATED for both internal and topical use. PAs cross the placenta and have teratogenic/abortifacient potential
• Lactation: CONTRAINDICATED. PAs detected in breast milk in animal models. If topical use is considered absolutely necessary, apply only to small intact skin areas away from the breast for minimal duration

Clinical Dosage

Recommended Forms and Doses

Key Dosing Principles

1. EXTERNAL USE ONLY — never internal
2. Duration limit: Maximum 4-6 weeks per year of continuous use (Commission E guideline)
3. Apply to INTACT SKIN only — not on open wounds, cuts, or abrasions
4. PA-depleted products preferred: Modern pharmaceutical products (Kytta-Salbe, Traumaplant) have controlled PA levels
5. Frequency: 2-4 applications daily for acute conditions; 2-3x daily for chronic conditions (OA)
6. Massage technique: Rub thoroughly into affected area for optimal dermal penetration

Key European Products

• Kytta-Salbe f (Merck, Germany) — comfrey root fluid extract ointment; most-studied product
• Traumaplant (Harras Pharma, Germany; Terry Naturally, US) — S. x uplandicum leaf extract cream; PA-free
• Kytta-Balsam (Germany) — related product
• Multiple German pharmacy comfrey preparations available

Sources

• Grube B et al. Efficacy of a comfrey root extract cream in the treatment of osteoarthritis of the knee. Phytomedicine. 2007;14:2-10.
• Predel HG et al. Efficacy of a comfrey root extract ointment in comparison to a diclofenac gel in the treatment of ankle distortions. Phytomedicine. 2005;12(10):707-714.
• Koll R et al. Efficacy and tolerance of a comfrey root extract in the treatment of ankle distortions. Phytomedicine. 2004;11(6):470-477.
• Giannetti BM et al. Efficacy and safety of comfrey root extract ointment in the treatment of acute upper or lower back pain. Arzneimittelforschung. 2010;60(3):106-113.
• Staiger C. Comfrey root: from tradition to modern clinical trials. Wien Med Wochenschr. 2013;163(3-4):58-64.
• Sowa I et al. A Symphytum officinale root extract exerts anti-inflammatory properties by affecting two distinct steps of NF-kB signaling. Front Pharmacol. 2019;10:289.
• Safety of medicinal comfrey cream preparations: The pyrrolizidine alkaloid lycopsamine is poorly absorbed through human skin. Regul Toxicol Pharmacol. 2020.
• German Commission E. Symphyti radix Monograph.
• ESCOP. Symphyti radix (Comfrey Root) Monograph.

Connections

• Compare with Arnica — both topical; comfrey has stronger RCT evidence for sprains/OA
• Compare with Capsicum — different topical mechanism; capsaicin for neuropathic component