What is Devil's Claw?

Sources
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Chrubasik S et al. "Effectiveness of Harpagophytum extract WS 1531 in the treatment of exacerbation of low back pain: a randomized, placebo-controlled, double-blind study." European Journal of Anaesthesiology. 16.2 (1999):118-29.

Dougados M et al. "Evaluation of the structure-modifying effects of diacerein in hip osteoarthritis: ECHODIAH, a three-year, placebo-controlled trial. Evaluation of the Chondromodulating Effect of Diacerein in OA of the Hip." Arthritis and Rheumatism. 44.11 (2001):2539-47.

Gagnier JJ et al. "Herbal medicine for low back pain." Cochrane Database of Systematic Reviews. 19.2 (2006):CD004504.

Gobel H et al. "Effects of Harpagophytum procumbens LI 174 (devil's claw) on sensory, motor und vascular muscle reagibility in the treatment of unspecific back pain." Schmerz. 15.1 (2001):10-8.

Huang TH et al. "Harpagoside suppresses lipopolysaccharide-induced iNOS and COX-2 expression through inhibition of NF-kappaB activation." Journal of Ethnopharmacology. 104.1-2 (2006):149-55.

Leblan D et al. "Harpagophytum procumbens in the treatment of knee and hip osteoarthritis. Four-month results of a prospective, multicenter, double-blind trial versus diacerhein." Joint Bone Spine. 67.5 (2000):462-7.

Mahomed IM and Ojewole JA. "Anticonvulsant activity of Harpagophytum procumbens DC [Pedaliaceae] secondary root aqueous extract in mice." Brain Research Bulletin. 69.1 (2006):57-62.

Mahomed IM and Ojewole JA. "Analgesic, antiinflammatory and antidiabetic properties of Harpagophytum procumbens DC (Pedaliaceae) secondary root aqueous extract." Phytotherapy Research. 18.12 (2004):982-9.

Stewart KM and Cole D. "The commercial harvest of devil's claw (Harpagophytum spp.) in southern Africa: the devil's in the details Journal of Ethnopharmacology. 100.3 (2005):225-36.

Wegener T and Lupke NP. "Treatment of patients with arthrosis of hip or knee with an aqueous extract of devil's claw (Harpagophytum procumbens DC.)." Phytotherapy Research. 17.10 (2003):1165-72.