Comfrey

Comfrey’s country names reflect its use: knitbone, boneset, bruisewort, blackwort.

The root is the stronger part. Grated or pounded into a wet paste and bound over a set fracture, it stiffens as it dries and helps to hold the limb.

The mucilaginous leaf is the gentler preparation. It is laid as a poultice over bruises, swellings and inflamed joints, or infused into oil for a salve.

Its traditional indications are injuries: fractures, sprains, strains, bruises, pulled muscles, inflamed joints and slow-healing grazes.

Comfrey was also eaten as a vegetable and drunk as a tea for more than 2,000 years ^{22Reference 22Mei et al. · 2010ReviewMetabolism, genotoxicity, and carcinogenicity of comfrey — reviewView study →}. It was taken internally for coughs and digestive complaints. That use has been abandoned because of the plant’s liver-toxic pyrrolizidine alkaloids, and regulators now recommend it for external use only ^{26Reference 26Brown et al. · 2016AnimalComparative toxicity of a reduced comfrey alkaloid extract and pure lycopsamine and intermedine in chicks — animal modelView study →}.

Acute ankle sprain is comfrey’s best-studied use. In a double-blind, placebo-controlled RCT (n=142, mean age 31.8), comfrey root ointment (Kytta-Salbe f) applied four times a day for 8 days clearly beat placebo on pain under pressure (p<0.0001) and on ankle swelling measured by the figure-of-eight method (p=0.0001). No adverse drug reactions were reported ^{3Reference 3Koll et al. · 2004RCTEfficacy and tolerance of a comfrey root extract in the treatment of ankle distortions — randomised, placebo-controlled, double-blindView study →}.

A multicentre, observer-blind trial (n=164) compared the same ointment with diclofenac gel in ankle sprain, applied four times a day for about a week. It was designed to show that comfrey was no worse than diclofenac, and it did ^{4Reference 4Predel et al. · 2005RCTEfficacy of a comfrey root extract ointment in comparison to a diclofenac gel in ankle distortions — randomised, multicenterView study →}. A later re-analysis of the same data for superiority found comfrey better than diclofenac on the primary tenderness measure (95% CI for the difference 19.08–103.09 h·N/cm²), with excellent tolerability in both groups ^{5Reference 5D’Anchise et al. · 2007RCTComfrey extract ointment in comparison to diclofenac gel in acute ankle sprains — randomised (superiority re-analysis)View study →}.

In a double-blind trial (n=203), a cream containing 10% of a fresh-herb concentrate of Russian comfrey (Traumaplant, S. × uplandicum) beat a 1% cream on pain and function at days 3–4 and day 7, and on swelling at days 3–4 ^{6Reference 6Kucera et al. · 2004RCTEfficacy and safety of topically applied Symphytum herb extract cream in ankle distortion — randomised, controlled, double-blindView study →}.

Clinical reviews also support its use for blunt injuries ^{1,30Reference 1Staiger · 2012ReviewComfrey: a clinical overview — reviewView study →Reference 30Staiger · 2013Clinical trialComfrey root: from tradition to modern clinical trials — reviewView study →}.

Gap: the trials tested two specific standardised products. A home-made salve or a generic comfrey cream of unknown strength is not the same thing.

Two randomised trials support topical comfrey root extract for acute back pain. In a double-blind, placebo-controlled, multicentre trial (n=120), patients applied 4 g of comfrey root ointment three times a day for 5 days. Pain on standardised movement fell by a median of about 95% with comfrey and about 38% with placebo, and the results agreed across all primary and secondary measures, including the Oswestry disability index ^{7Reference 7Giannetti et al. · 2010RCTComfrey root extract ointment for acute upper or lower back pain — double-blind, randomised, placebo-controlled, multicentreView study →}.

A three-arm RCT (n=379) tested a cream of 35% comfrey root extract plus 1.2% methyl nicotinate, a warming rubefacient, against methyl nicotinate alone and placebo. The combination beat both (p<0.0001) ^{8Reference 8Pabst et al. · 2013RCTComfrey root extract plus methyl nicotinate in acute back pain — randomised, placebo-controlled, three-armView study →}.

The 2014 Cochrane review of herbal medicine for low-back pain found low-quality evidence that the comfrey ointment is better than placebo for short-term pain ^{28Reference 28Oltean et al. · 2014Meta-analysisHerbal medicine for low-back pain — systematic review and meta-analysis (Cochrane)View study →}.

The trials ran for five days and tested acute pain only. There is no evidence for chronic back pain, and the three-arm trial combined comfrey with a counter-irritant.

In a double-blind, placebo-controlled RCT (n=220), comfrey root ointment 6 g/day for 3 weeks reduced the VAS pain score by 54.7%, against 10.7% with placebo (p<0.001). The WOMAC index improved in parallel ^{9Reference 9Grube et al. · 2007RCTComfrey root extract ointment in painful osteoarthritis of the knee — double-blind, randomised, placebo-controlledView study →}. The 2013 Cochrane review of topical herbal treatments for osteoarthritis judged, from this single trial, that comfrey probably improves pain, with no more side effects than placebo ^{29Reference 29Cameron et al. · 2013Systematic reviewTopical herbal therapies for treating osteoarthritis — systematic review (Cochrane)View study →}.

Two further RCTs tested comfrey in combination products. A standardised comfrey extract with pharmaceutical tannic acid (“4Jointz”, n=133, 12 weeks) reduced knee pain modestly versus placebo but did not change inflammatory (IL-6) or cartilage-breakdown (CTX-2) markers. Local rash was more frequent on the active cream (21% vs 1.6%) ^{10Reference 10Laslett et al. · 2012RCTLaslett, L. L., et al. (2012). 4Jointz (comfrey extract + tannic acid) reduces knee pain over 12 weeks in clinical knee osteoarthritis — randomised, placebo-controlled. Osteoarthritis and Cartilage. https://pubmed.ncbi.nlm.nih.gov/22863612/View study →}.

Creams of 10% and 20% comfrey root extract with tannic acid and eucalyptus (n=43, 6 weeks) beat a eucalyptus reference cream on WOMAC pain, stiffness and function ^{11Reference 11Smith et al. · 2011RCTComfrey root extract and tannic acid creams in osteoarthritis of the knee — randomised, placebo-controlled, double-blindView study →}.

Gap: the two combination trials cannot separate comfrey’s own contribution from the tannic acid, and the effect in the longer 12-week trial was modest.

The wound-healing trials compared a 10% cream with a 1% cream rather than with placebo. In a double-blind study of 108 children aged 3–12 with fresh abrasions, the 10% aerial-part concentrate reached 50% healing about 0.9 days sooner than the 1% cream (p=0.0002) ^{13Reference 13Barna et al. · 2012RCTWound-healing effects of a Symphytum herb extract cream in children — randomised, controlled, double-blindView study →}. A larger trial (n=278) found a faster early reduction in wound size (49% vs 29% per day) and complete healing in 4.08 days against 7.05 days ^{14Reference 14Barna et al. · 2007RCTWound-healing effects of a Symphytum herb extract cream — randomised, controlled, double-blindView study →}.

In an in-vitro skin model, comfrey cream sped up regrowth of the outer skin layer over days 4–7 ^{15Reference 15Dähnhardt et al. · 2020In vitroEpidermal regeneration induced by comfrey extract — in vitro (light and electron microscopy)View study →}, and in rats comfrey extract creams increased collagen deposition and reduced inflammation ^{16,17Reference 16Mârza et al. · 2024AnimalHealing of skin wounds in rats using creams based on Symphytum officinale extract — animal modelView study →Reference 17Araújo et al. · 2012AnimalIn vivo wound-healing effects of Symphytum officinale leaves extract — animal modelView study →}.

Allantoin and rosmarinic acid are the presumed active compounds ^{16Reference 16Mârza et al. · 2024AnimalHealing of skin wounds in rats using creams based on Symphytum officinale extract — animal modelView study →}.

Gap: this use applies only to clean, superficial grazes, not to deep or open wounds, and the EU monograph advises against applying comfrey root to broken or irritated skin ^{31Reference 31Committee on Herbal Medicinal Products ( · 2015ReviewEuropean Union herbal monograph on Symphytum officinale L., radix (EMA/HMPC/572846/2009 Corr1) — regulatory monographView study →}. Because the comparator was a weaker comfrey cream, part of the measured benefit is a dose effect.

A double-blind, randomised, multicentre trial (n=215) tested a 10% fresh-comfrey aerial concentrate against a 1% reference cream in patients with upper- and lower-back muscle pain ^{12Reference 12Kucera et al. · 2005RCTTopical Symphytum herb concentrate cream against myalgia — randomised, controlled, double-blindView study →}.

The stronger cream gave significantly greater relief of pain on movement (p<5×10⁻⁹), pain at rest and pain on pressure, with a number needed to treat of 3.2 and a faster onset. Tolerability was good to excellent ^{12Reference 12Kucera et al. · 2005RCTTopical Symphytum herb concentrate cream against myalgia — randomised, controlled, double-blindView study →}.

It is one trial, with a low-dose comparator rather than placebo, and it has not been replicated.

In primary human endothelial cells, a hydroalcoholic comfrey root extract blocked interleukin-1-induced expression of the pro-inflammatory markers E-selectin, VCAM-1, ICAM-1 and COX-2 in a dose-dependent way. It inhibited NF-κB signalling at two separate steps ^{18Reference 18Seigner et al. · 2019In vitroA Symphytum officinale root extract exerts anti-inflammatory properties by affecting two distinct steps of NF-κB signaling — in vitroView study →}.

The mucilage-depleted fraction was the more active, which points to the phenolics rather than the soothing polysaccharides ^{18Reference 18Seigner et al. · 2019In vitroA Symphytum officinale root extract exerts anti-inflammatory properties by affecting two distinct steps of NF-κB signaling — in vitroView study →}.

A review of the genus collects further preclinical anti-inflammatory data across Symphytum species, and attributes the activity to rosmarinic acid and related polyphenols alongside allantoin ^{21Reference 21Mahmoudzadeh et al. · 2022ReviewAnti-inflammatory properties of the genus Symphytum L. — reviewView study →}.

The mechanism has been shown in cultured human cells rather than inflamed human tissue. The one trial that measured IL-6 saw no change ^{10Reference 10Laslett et al. · 2012RCTLaslett, L. L., et al. (2012). 4Jointz (comfrey extract + tannic acid) reduces knee pain over 12 weeks in clinical knee osteoarthritis — randomised, placebo-controlled. Osteoarthritis and Cartilage. https://pubmed.ncbi.nlm.nih.gov/22863612/View study →}.

Comfrey root and leaf extracts show consistent antioxidant activity in laboratory assays. A root extract scavenged DPPH and ABTS radicals and inhibited 15-lipoxygenase. Rosmarinic acid was the main phenolic (7.55 mg/g extract), and caffeic-acid oligomers, isomers of salvianolic acid A, B and C, were quantified for the first time ^{20Reference 20Trifan et al. · 2018In vitroSalvianolic acids among antioxidant polyphenols in comfrey root — in vitroView study →}.

A separate study found that a root extract rich in rosmarinic, caffeic, chlorogenic and p-coumaric acids was non-toxic to human skin fibroblasts, increased their growth, and showed high DPPH/FRAP antioxidant capacity ^{19Reference 19Sowa et al. · 2018In vitroProliferative and antioxidant activity of Symphytum officinale root extract — in vitroView study →}.

This is entirely in vitro, with no human endpoint.

Internal use. Comfrey contains as many as 14 pyrrolizidine alkaloids, including symphytine, echimidine, lycopsamine and intermedine. Their metabolites bind DNA in liver cells, and comfrey is mutagenic in the liver and causes tumours in experimental animals ^{22Reference 22Mei et al. · 2010ReviewMetabolism, genotoxicity, and carcinogenicity of comfrey — reviewView study →}. Rats fed a diet of 8% comfrey root for 12 weeks showed cancer-related gene changes in the liver similar to those caused by riddelliine, a known carcinogenic alkaloid ^{23Reference 23Guo et al. · 2007AnimalComparison of gene expression profiles altered by comfrey and riddelliine in rat liver — animal modelView study →}. In people, eating comfrey leaves or drinking comfrey tea has been linked to veno-occlusive liver disease, including a fatal case in a 23-year-old man ^{24,25Reference 24Yeong et al. · 1990Case reportHepatic veno-occlusive disease associated with comfrey ingestion — case reportView study →Reference 25Ridker et al. · 1989Case reportHepatotoxicity due to comfrey herb tea — case reportView study →}.

Regulation. Regulators and international health bodies recommend comfrey for external use only ^{26Reference 26Brown et al. · 2016AnimalComparative toxicity of a reduced comfrey alkaloid extract and pure lycopsamine and intermedine in chicks — animal modelView study →}. The EU herbal monograph accepts comfrey root only as a traditional topical remedy for minor sprains and bruises ^{31Reference 31Committee on Herbal Medicinal Products ( · 2015ReviewEuropean Union herbal monograph on Symphytum officinale L., radix (EMA/HMPC/572846/2009 Corr1) — regulatory monographView study →}.

Use on the skin. Little is known about how much alkaloid passes through the skin ^{31Reference 31Committee on Herbal Medicinal Products ( · 2015ReviewEuropean Union herbal monograph on Symphytum officinale L., radix (EMA/HMPC/572846/2009 Corr1) — regulatory monographView study →}. The EU monograph limits the alkaloid content of a comfrey root product to less than 1 µg a day, rules out broken or irritated skin and contact with the eyes, and sets a maximum of 10 days per course ^{31Reference 31Committee on Herbal Medicinal Products ( · 2015ReviewEuropean Union herbal monograph on Symphytum officinale L., radix (EMA/HMPC/572846/2009 Corr1) — regulatory monographView study →}. In traditional practice, use is also kept to a few weeks a year.

Root and leaf. The root carries far more pyrrolizidine alkaloid than the leaf, and root content varies widely between sources. Some roots on the Polish market exceeded the daily amount considered safe ^{27Reference 27Kimel et al. · 2023LC-MS/MS evaluation of pyrrolizidine alkaloids in comfrey roots and leaves — analyticalView study →}. Leaf-based preparations, which carry less alkaloid, are preferred ^{27Reference 27Kimel et al. · 2023LC-MS/MS evaluation of pyrrolizidine alkaloids in comfrey roots and leaves — analyticalView study →}, as are extracts with the alkaloids reduced.

Deep and open wounds. Comfrey is kept for closed injuries and clean, superficial grazes. On a deep or dirty wound it may close the skin over tissue that has not healed underneath, trapping infection.

Who should not use it. Comfrey is not recommended in pregnancy or breastfeeding, or for anyone under 18 ^{31Reference 31Committee on Herbal Medicinal Products ( · 2015ReviewEuropean Union herbal monograph on Symphytum officinale L., radix (EMA/HMPC/572846/2009 Corr1) — regulatory monographView study →}. People with liver disease should avoid it.