• Balagué F, Mannion AF, Pellisé F, Cedraschi C. 2012. Non-specific low back pain. Lancet 379: 482491.
  • Committee for Proprietary Medicinal Products (CPMP). 2002. Note for guidance on clinical investigation of medicinal products for treatment of nociceptive pain. CPMP/EWP/612/00., accessed Nov 4, 2011.
  • D'Anchise R, Bulitta M, Giannetti B. 2007. Comfrey extract ointment in comparison to a diclofenac gel in the treatment of acute unilateral ankle sprains (distortions). Arzneim-Forsch Drug Res 57: 712716.
  • Devogelaer JP, Dreiser RL, Abadie E, et al. 2003. Guidelines for clinical studies assessing the efficacy of drugs for the management of acute low back pain. Clin Exp Rheumatol 21: 691694.
  • Englert K, Mayer JG, Staiger C. 2005. Symphytum officinale L. Der “Beinwell“ in der europäischen Pharmazie- und Medizingeschichte. Z Phytother 26: 158168.
  • European Scientific Cooperative on Phytotherapy (ESCOP). 2009. Symphyti radix, Comfrey root. In ESCOP Monographs: The Scientific Foundation for Herbal Medicinal Products (2nd ed. Suppl 2009). Thieme Verlag: Stuttgart; 249254.
  • Giannetti BM, Staiger C, Bulitta M, Predel HG. 2010. Efficacy and safety of a comfrey root extract ointment in the treatment of acute upper or lower back pain: results of a double-blind, randomised, placebo controlled, multicentre trial. Br J Sport Med 44: 637641.
  • Grube B, Grünwald J, Krug L, Staiger C. 2007. 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 14: 210.
  • Klingenburg S. 2004. Wärmendes Topikum mit Symphytum officinale. Erfahrungsheilkunde 53: 350354.
  • Koll R, Buhr M, Dieter R, et al. 2004. Efficacy and tolerance of a comfrey root extract (Extr. Rad. Symphyti) in the treatment of ankle distortions: results of a multicenter, randomized, placebo-controlled, double-blind study. Phytomedicine 11: 470477.
  • Lenhart P, Seibert W. 2001. Funktionelles Bewegungstraining (6th ed.) Urban Fischer Verlag: Jena; 3043.
  • McCarberg BH. 2010. Acute back pain: benefi ts and risks of current treatments. Curr Med Res Opin 26: 179190.
  • Petersen G, Lorkowski G, Kasper FR, Gottwald R, Lücker PW. 1993. Anti-inflammatory activity of a pyrrolizidine alkaloid-free extract of roots of Symphytum officinale in humans. Planta Med 59(Suppl.): A703A704.
  • Predel HG, Giannetti B, Koll R, Bulitta M, Staiger C. 2005. Efficacy of a comfrey root extract ointment in comparison to a diclofenac gel in treatment of ankle distortions: results of an observer-blind, randomized, multicenter study. Phytomedicine 12: 707714.
  • Smith DB, Jacobson BH. 2011. 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. J Chiropr Med 10: 147156.
  • Staiger C. 2005. Beinwell – eine moderne Arzneipflanze. Z Phytother 26: 169173.
  • Staiger C. 2007. Beinwell – Stand der klinischen Forschung. Z Phytother 28: 110114.
  • Staiger C. 2012. Comfrey: A Clinical Overview. Phytother Res. doi: 10.1002/ptr.4612 [Epub ahead of print]