Comfrey

Comfrey, also known as knitbone, is used externally for speeding up the healing of clean wounds, broken bones, pulled ligaments and sprains, varicose veins, burns, hernias and for fostering proper scar formation. Author of Medical Herbalism, David Hoffmann, says care should be taken with very deep wounds as external application of comfrey can cause tissue to form over the wound, before it is healed deeper down, which can lead to abscess. In the 17th century Nicholas Culpeper mentioned comfrey in his enlarged version of The English Physician in 1656. He stated: “It is said to be so powerful to consolidate and knit together… outward Wounds and Sores in the Fleshy or Sinewy part of the Body whatsoever.” Today this historical statement is widely supported by modern clinical data. Multiple randomised controlled trials have demonstrated the efficacy and safety of comfrey preparations for the topical treatment of pain, inflammation and swelling of muscles and joints in degenerative arthritis, acute myalgia in the back, sprains, contusions and strains after sports injuries and accidents, also in children aged three and over.

One double-blind, multicentre, randomised clinical trial, in patients with acute upper or lower back pain, showed that comfrey root extract has a remarkably potent and clinically relevant effect in reducing acute back pain. In the study, conducted over five days, 120 patients were treated with 4g of comfrey or placebo ointment three times a day. In the course of the trial the pain intensity on active standardised movement decreased on average approximately 95.2% in the comfrey group and 37.8% in the placebo group.

In the past comfrey was used internally in bronchitis and irritable cough, to soothe and reduce irritation while promoting expectoration, however it is now for external use only after being surrounded by controversy. Comfrey contains varying amounts of pyrrolizidine alkaloids (PAs) which are substances that are potentially toxic to humans by causing liver damage. Long term studies in rats, which were unethically fed large amounts of comfrey, demonstrated that PAs were hepatotoxic, carcinogenic and mutagenic however there have been no human clinical trials regarding comfrey ingestion. There are four case studies implicating comfrey ingestion in veno-occlusive disease in the liver however there are also multiple confounding factors in these case studies, such as concomitant use of hepatotoxic drugs and malnutrition. It is due to these potential risks that comfrey is recommended for external use only.

References

Hoffmann D. Medical Herbalism. Rochester: Healing Arts Press. 2003. p. 586

Staiger C. Comfrey: a clinical overview. Phytother Res. 2012 Oct;26(10):1441-8. doi: 10.1002/ptr.4612. Epub 2012 Feb 23. PMID: 22359388; PMCID: PMC3491633.

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 Medicin. 2010;44:637-641.

[iv] de la Forêt R. Comfrey Monograph. Herb Mentor c2022 Learningherbs.com  (updated 31 Jul 2017; accessed 2 Sep 2022). Available from https://herbmentor.learningherbs.com/herb/comfrey/