H. procumbens are mainly found in the eastern and south eastern parts of Namibia, Southern Botswana and the Kalahari region of the Northern Cape, South Africa. H. Zeyheri is found in the northern parts of Namibia (Ovamboland) and southern Angola. The active ingredient is harpagoside (structure at PubChem [1]) with values ranging in both species from 1.0% to 3.3%.

The name "devil's claw" is also used for several species of North American plants in the genus Proboscidea, as well as Urtica dioica and certain species of Pisonia.

The constituents thought to be responsible for the anti-inflammatory effects of Devil's Claw (dried secondary tubers) are iridoid glycosides, particularly harpagoside (trans-cinnamoyl harpagide) including small amounts of trans-coumaroyl harpagide, procumbide and plant sterols.^[1] The British Herbal Pharmacopoeia recognises Devil's Claw as having analgesic, sedative and diuretic properties. Most studies involve chronic use, rather than acute treatment of pain. This herbal drug is also official in the European Pharmacopoeia and a component of a number of OTC preparations and dietary supplements for its claimed anti-rheumatic effects.

Several studies have been performed using Doloteffin, a standardized preparation of Devil's Claw. Due to the natural variability of herbal extracts, the results of studies using different products and preparations are difficult to compare. A series of small-scale studies completed in Germany found that H. procumbens was comparable to Vioxx in the treatment of chronic low back pain,^[2] and was well-tolerated after more than four years of treatment with H. procumbens alone.^[3] H. procumbens also seems efficacious in the treatment of arthritis-caused hip and knee pain. An author involved in several studies on Devil's Claw and pain relief had the general conclusion that a minimum 50 mg per dose standardized extract was an alternative to synthetic analgesics with a low risk of adverse events.^[4] A separate 2006 systematic review of herbal medications for low back pain reached the conclusion that a standardized daily dose between 50 and 100 mg of harpagoside performed better than a placebo, and an unspecified dose of harpagoside demonstrated relative equivalence to 12.5 mg per day of Vioxx.^[5]