Comfrey for Osteoarthritis and Back Pain

An acute ankle sprain is a one-week problem. A sore knee and a bad back are not — they are conditions people live with for years, which changes what a treatment has to prove. It is one thing to help a swollen ankle settle over eight days; it is another to help a knee that has hurt for six and a half years.

Comfrey has been tested for both. The knee osteoarthritis trial is the largest and best-known comfrey study ever run, and it is the only comfrey trial ever appraised by an independent Cochrane review — which rated the evidence moderate quality and concluded that comfrey extract gel probably improves pain. That is a careful, hedged, genuinely independent endorsement, and it is more than most topical herbs ever get.

⚠ The safety rule that governs everything on this page: comfrey goes on the skin, never in the mouth. Its pyrrolizidine alkaloids cause hepatic veno-occlusive disease — irreversible, sometimes fatal liver injury — with documented human deaths, including from comfrey tea. Oral comfrey is banned or restricted in the United States, the United Kingdom, Germany, Canada and Australia. Those alkaloids also pass through broken skin, so topical use belongs on intact skin only, for a short course (typically 10 days), never in pregnancy or breastfeeding, and not on children. This is the point where the chronic-condition framing gets dangerous: a knee that hurts every day invites daily, indefinite use, and indefinite use is exactly what comfrey does not permit.

Table of Contents

1. The 220-Patient Knee Trial
2. What Cochrane Independently Concluded
3. The Second, Smaller Knee Trial
4. Acute Back Pain: 120 Patients, Five Days
5. Muscle Pain and the Dose-Response Trial
6. How Big Are These Effects, Really?
7. The Chronic-Use Problem
8. Practical Use for a Joint or a Back
9. Where It Fits Alongside Standard Care
10. The Funding Problem
11. Cautions and Contraindications
12. Key Research Papers
13. Connections

The 220-Patient Knee Trial

Grube and colleagues published this in Phytomedicine in 2007, and it remains the flagship comfrey study.

• Design: randomised, double-blind, bicentre, placebo-controlled.
• Who: 220 patients with painful osteoarthritis of the knee — 153 women, 67 men, average age 57.9 years, with symptoms present for an average of 6.5 years. These were not people with a mild twinge.
• What: 6 g of comfrey root ointment daily, given as 2 g three times a day, for three weeks. The comparator was an identical placebo ointment.
• Primary outcome: total pain score on a 100 mm visual analogue scale (VAS), combining pain at rest and pain on movement.

The result. The comfrey group’s VAS total score fell by 51.6 mm (a 54.7 % reduction). The placebo group’s fell by 10.1 mm (10.7 %). The difference between groups was 41.5 mm (95 % confidence interval 34.8 to 48.2 mm), p<0.001. The WOMAC score — the standard osteoarthritis instrument covering pain, stiffness and physical function — moved in parallel: down 60.4 mm (58.0 %) with comfrey versus 14.7 mm (14.1 %) with placebo.

Two further details are worth noticing. The gap between groups widened systematically over the three weeks rather than appearing all at once, which is the pattern you would expect from a treatment doing something cumulative rather than from an initial burst of enthusiasm. And the secondary measures — knee range of motion measured by goniometer, SF-36 quality of life, and clinical global impression — all favoured comfrey at p<0.001.

What Cochrane Independently Concluded

This is the part that separates comfrey from the crowd of herbs with impressive-sounding manufacturer trials.

In 2013, Cameron and Chrubasik published a Cochrane review, Topical herbal therapies for treating osteoarthritis, covering seven trials of six different plant products in 785 participants. Cochrane reviews are produced by independent authors under a fixed methodology, with formal risk-of-bias assessment and GRADE quality ratings — they are not sympathetic to weak herbal evidence, and the same review concluded that capsicum extract gel probably does not improve pain or knee function while causing burning and irritation in 80 % of users.

On comfrey, the review reported: moderate evidence from a single trial of 220 people with knee osteoarthritis suggested that comfrey extract gel probably improves pain without increasing adverse events. Specifically — at three weeks, mean pain in the placebo group was 83.5 points on a 100-point scale; comfrey reduced pain by a mean of 41.5 points (95 % CI −48 to −34), an absolute reduction of 42 %. Adverse events were lower in the comfrey group: 6 % (7 of 110) versus 14 % (15 of 110) on placebo.

Three honest qualifications that the review itself makes. First, moderate quality means further research is likely to change the estimate — it is not the top tier. Second, this rests on a single trial; nothing was pooled, because there was nothing to pool it with. Third, function was not reported in a form the reviewers could extract, so the Cochrane conclusion covers pain only. The overall verdict of the review was that the quality and quantity of research on topical plant products remains insufficient, and comfrey was the best of a thin field rather than a proven therapy.

The Second, Smaller Knee Trial

An American group (Smith and Jacobson, Journal of Chiropractic Medicine, 2011) tested a different formulation: a botanical cream blending comfrey root extract with tannic acid and eucalyptus. Forty-three participants aged 45 to 83 with diagnosed primary knee osteoarthritis were randomised to a 10 % comfrey cream, a 20 % comfrey cream, or a eucalyptus reference cream, applied three times a day for six weeks, with WOMAC assessments every two weeks.

Both active creams beat the reference cream on WOMAC pain, stiffness and daily function (all p<0.01). Adverse events were minor: two participants in each active group developed temporary rash and itching that resolved when the application was modified.

Read this one cautiously. Forty-three people across three arms is roughly fourteen per group — small enough that chance plays a large role. The comparator was a eucalyptus cream rather than a true inert placebo. And because the product blended comfrey with tannic acid, the trial cannot say which ingredient did the work. It is supportive, not confirmatory. Its most useful contribution is that it is the only comfrey osteoarthritis trial that ran for six weeks — longer than the standard European duration limit for comfrey root preparations, which is a reason to note the trial rather than to imitate it.

Acute Back Pain: 120 Patients, Five Days

Giannetti and colleagues (British Journal of Sports Medicine, 2010) ran a double-blind, multicentre, randomised, placebo-controlled trial in 120 patients with acute upper or lower back pain, mean age 36.9 years. Treatment was 4 g of comfrey root ointment three times a day for 5 days, with four study visits.

The primary outcome was the area under the curve of VAS pain during standardised active movement. The reported result was large: pain on active standardised movement fell by a median of approximately 95.2 % in the comfrey group versus 37.8 % on placebo. Secondary outcomes — pain at rest, pressure algometry, Oswestry disability index, analgesic consumption, and global assessments by both patient and investigator — all pointed the same way. The authors also reported a measurable effect within one hour of the first application.

Be appropriately sceptical of a 95 % median reduction. Acute non-specific back pain is a condition with a famously steep natural recovery curve — most episodes improve substantially within days no matter what is done — and the placebo arm’s 37.8 % improvement shows that curve operating. The gap between the arms is the real finding, and it is a big one. But this is a single trial, sponsored, and never independently replicated, and no Cochrane review has appraised it. Treat it as promising rather than established. It also says nothing whatsoever about chronic back pain, which is a different clinical problem.

Muscle Pain and the Dose-Response Trial

Kucera and colleagues (Advances in Therapy, 2005) studied 215 patients with pain in the upper and lower back classified as myalgia — muscle pain rather than joint or disc pain. This trial used the comfrey herb cream rather than the root ointment, and it used an unusual comparator: 104 patients received the 10 % cream and 111 received a 1 % version of the identical cream.

The stronger cream produced significantly greater improvement in pain on active motion (p<5×10⁻⁹), pain at rest (p<0.001) and pain on palpation (p=5×10⁻⁵), with faster onset of effect. The authors calculated a number needed to treat of 3.2 — roughly, for every three people treated with the strong cream instead of the weak one, one additional person got a meaningful benefit. For a topical product that is a respectable figure.

The design deserves credit and a caveat. Its virtue is that it demonstrates dose-response: more comfrey produced more effect, which is one of the standard arguments that a real pharmacological action is present rather than ritual and expectation. Its limitation is that both arms contained comfrey, so the trial cannot estimate the placebo effect at all — and rubbing cream into a sore back three times a day is a treatment with a substantial placebo component built in.

How Big Are These Effects, Really?

Numbers like “41.5 mm on a 100 mm scale” are hard to feel. Some context:

• On a 100 mm pain VAS, the minimum clinically important difference — the smallest change a patient reliably notices — is usually put at around 10 to 20 mm. A 41.5 mm between-group difference is therefore two to four times the threshold of noticeability, which is unusually large for any osteoarthritis treatment.
• For comparison, oral non-steroidal anti-inflammatories in knee osteoarthritis typically produce effect sizes corresponding to something in the region of 10 mm over placebo. Topical NSAIDs are broadly similar. A herbal ointment reporting four times that should raise an eyebrow, not just hopes.
• The most likely explanation for the gap is not that comfrey is four times better than diclofenac. It is that a single sponsored trial with a highly favourable design produces a larger estimate than a pooled literature does — which is exactly why Cochrane graded it moderate rather than high, and exactly why an independent replication would be valuable.

The honest summary: comfrey ointment very probably reduces knee osteoarthritis pain by an amount patients would notice. The true size is likely smaller than 41.5 mm, and nobody yet knows how much smaller.

The Chronic-Use Problem

This is where comfrey and chronic conditions collide, and it deserves a section of its own.

Knee osteoarthritis lasts for decades. Back pain recurs. The natural way to use something that helps is to keep using it — a jar in the bathroom cupboard, applied most days, for years. Comfrey does not permit that.

Pyrrolizidine alkaloids are cumulative toxins. The clearest illustration comes from the case of a 49-year-old woman who developed hepatic veno-occlusive disease after consuming an estimated minimum of 85 mg of alkaloids over six months from a ground comfrey root supplement — approximately 15 micrograms per kilogram of body weight per day. She did not take a large dose once; she took a small dose repeatedly. Skin absorption is far lower than oral absorption — measurably so — but it is not zero, and the same arithmetic of accumulation applies.

That is why regulators put a clock on it. The European herbal monograph for comfrey root preparations limits self-treatment to about 10 days; German dosing rules cap total external comfrey use at roughly four to six weeks per year. The knee trial that produced the headline number ran for three weeks, and there is no trial of any duration beyond six.

The practical implication: comfrey is a tool for a flare, not a maintenance therapy. Use it for the fortnight when the knee is bad, then stop and go back to the things you can do indefinitely — quadriceps strengthening, weight management, walking, topical NSAIDs, paracetamol. If you find yourself reaching for comfrey most weeks, that is a signal that the underlying problem needs a proper management plan, not a bigger jar.

Practical Use for a Joint or a Back

What to check before you buy. The species (Symphytum officinale or S. × uplandicum); the plant part (root or herb); the extract ratio or percentage of concentrate; and an explicit pyrrolizidine alkaloid statement. Expect to pay roughly what a branded diclofenac gel costs. A tube that says only “with comfrey” alongside twelve other botanicals is a cosmetic, not a version of what was tested.

Where It Fits Alongside Standard Care

Comfrey ointment is a symptomatic treatment. It does nothing to cartilage, nothing to a degenerating disc, and nothing to the underlying course of osteoarthritis. What it may do is make a painful fortnight more tolerable, which has a real downstream value: less pain means more movement, and more movement is the single intervention with the best long-term evidence in knee osteoarthritis.

Reasonable ways to use it:

1. As a first step before oral NSAIDs. If you have gastrointestinal, kidney or cardiovascular reasons to avoid oral ibuprofen or naproxen, a topical is the standard alternative, and comfrey is a topical with trial evidence. So is diclofenac gel — and the direct comparisons in ankle sprain found them comparable.
2. As a flare treatment on top of a maintenance plan. The plan is exercise, strength and weight; comfrey covers the bad weeks.
3. Not as a substitute for assessment. A knee that locks, gives way, or swells rapidly, or back pain with leg weakness, numbness in the saddle area, or bladder or bowel change, needs a clinician the same day — not an ointment.

The Funding Problem

It has to be said plainly: the flagship trials on this page were run by the manufacturers. The knee trial’s first author was affiliated with Merck Selbstmedikation, which makes the root ointment. So were the ankle-sprain and back-pain trials. The most widely cited comfrey review was written by an author from the same company.

Industry sponsorship is not fraud, and these were properly randomised, blinded, placebo-controlled trials with objective instruments. But the empirical literature on sponsorship is consistent: company-funded trials report larger benefits and fewer harms than independently funded ones testing the same thing. An independent scoping review of comfrey’s external uses (Frost, MacPherson and O’Meara, 2013) reviewed this whole body of work and reached the same verdict — promising evidence, methodological limitations, and a clear need for research the manufacturers did not pay for.

The counterweight is the Cochrane review, which was independent, applied formal risk-of-bias assessment, and still concluded that comfrey gel probably improves pain. That is the strongest single sentence anyone can honestly write about comfrey and osteoarthritis — and note how carefully it is hedged.

Cautions and Contraindications

⚠ Never take comfrey internally. Not as tea, capsules, tincture, powder or leaf. Pyrrolizidine alkaloids cause hepatic veno-occlusive disease, documented in fatal human cases. See Never Take It Internally.

• Intact skin only. Broken skin removes the barrier that keeps dermal alkaloid absorption low.
• Respect the clock. About 10 days per course; roughly four to six weeks total per year under German external-use rules. Chronic pain is not a licence for chronic use.
• Not in pregnancy or breastfeeding, topical included — alkaloids cross the placenta and enter milk, and the fetal and infant liver is the target organ.
• Not on children; observe the product’s age limit, generally 12 or 18 years for root preparations.
• Avoid with any liver disease — hepatitis, cirrhosis, fatty liver — and with hepatotoxic medication such as methotrexate, azathioprine, isoniazid or high-dose paracetamol. If you have osteoarthritis or inflammatory arthritis and are on methotrexate, this applies to you specifically.
• Do not apply to large areas of the body repeatedly. Total exposure scales with treated surface area, not with how bad the pain feels.
• Skin reactions. Contact dermatitis is uncommon but real — two participants per active group in the small American knee trial. Stop if the skin becomes red, itchy or blistered.
• Do not combine with a heat wrap or occlusive dressing unless the label says so; both increase absorption.
• Red flags that need a doctor, not an ointment: a hot, hugely swollen joint (possible septic arthritis or gout); back pain with fever, unexplained weight loss, or a history of cancer; back pain with leg weakness, saddle numbness or loss of bladder or bowel control; or a knee that locks or gives way.

Key Research Papers

Every identifier below was checked live against NCBI E-utilities — title, first author, journal and year all had to match before a PMID was written.

1. Grube B, Grünwald 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(1):2–10. — 220 patients, 6 g/day for 3 weeks; VAS fell 51.6 mm versus 10.1 mm on placebo, between-group difference 41.5 mm (95 % CI 34.8–48.2).
2. Cameron M, Chrubasik S. Topical herbal therapies for treating osteoarthritis. Cochrane Database of Systematic Reviews. 2013;(5):CD010538. — The independent verdict: moderate-quality evidence that comfrey extract gel probably improves pain; adverse events 6 % versus 14 % on placebo; function not reported.
3. Smith DB, Jacobson BH. Effect of a blend of comfrey root extract (Symphytum officinale L.) and tannic acid creams in the treatment of osteoarthritis of the knee: randomized, placebo-controlled, double-blind, multiclinical trials. Journal of Chiropractic Medicine. 2011;10(3):147–156. — Only 43 participants across three arms, and the active cream also contained tannic acid; supportive but not confirmatory.
4. Giannetti BM, Staiger C, Bulitta M, Predel HG. 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(9):637–641. — 120 patients, 4 g three times daily for 5 days; median pain on movement fell 95.2 % versus 37.8 %. Single trial, sponsored, unreplicated.
5. Kucera M, Barna M, Horàcek O, Kàlal J, Kucera A, Hladìkova M. Topical Symphytum herb concentrate cream against myalgia: a randomized controlled double-blind clinical study. Advances in Therapy. 2005;22(6):681–692. — 215 patients; 10 % cream versus 1 % cream, number needed to treat 3.2. Dose-response, but no true placebo arm.
6. Kucera M, Kálal J, Polesná Z. Effects of Symphytum ointment on muscular symptoms and functional locomotor disturbances. Advances in Therapy. 2000;17(4):204–210.
7. Predel HG, Giannetti B, Koll R, Bulitta M, Staiger C. 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. — The head-to-head against a standard topical NSAID; useful context for whether comfrey is competitive.
8. Frost R, MacPherson H, O’Meara S. A critical scoping review of external uses of comfrey (Symphytum spp.). Complementary Therapies in Medicine. 2013;21(6):724–745. — Independent, and blunt about industry funding and methodological limits.
9. Seigner J, Junker-Samek M, Plaza A, et al. A Symphytum officinale root extract exerts anti-inflammatory properties by affecting two distinct steps of NF-κB signaling. Frontiers in Pharmacology. 2019;10:289. — Cell culture; suppression of COX-2, E-selectin, VCAM-1 and ICAM-1 in human endothelial cells.
10. Sowa I, Paduch R, Strzemski M, et al. Proliferative and antioxidant activity of Symphytum officinale root extract. Natural Product Research. 2018;32(5):605–609. — Cell culture; quantifies allantoin plus rosmarinic, caffeic, chlorogenic, p-coumaric and p-hydroxybenzoic acids.
11. Staiger C. Comfrey root: from tradition to modern clinical trials. Wiener Medizinische Wochenschrift. 2013;163(3–4):58–64. — A manufacturer-affiliated overview of the trial programme.
12. Ridker PM, Ohkuma S, McDermott WV, Trey C, Huxtable RJ. Hepatic venocclusive disease associated with the consumption of pyrrolizidine-containing dietary supplements. Gastroenterology. 1985;88(4):1050–1054. — The case that demonstrates cumulative, low-level alkaloid exposure is enough to cause disease.

Live PubMed Searches

1. Comfrey and knee osteoarthritis
2. Comfrey and back pain
3. Topical herbal therapies for osteoarthritis
4. Topical NSAIDs for knee osteoarthritis
5. WOMAC and clinically important difference
6. Industry sponsorship and trial outcomes
7. Symphytum officinale anti-inflammatory activity
8. Exercise therapy for knee osteoarthritis

Connections

• All Herbs
• Comfrey Benefits — hub
• Comfrey — main topic page
• Topical Use for Sprains and Bruises
• Wound Healing and Allantoin
• ⚠ Never Take It Internally
• Orthopedics — joints, back and musculoskeletal pain
• Butterbur — another pain herb with the same alkaloid problem
• Calendula — a gentler topical herb
• Marshmallow Root — soothing mucilage, no alkaloids

Back to Table of Contents