Scientific Name(s): Harpagophytum procumbens, subsp. procumbens DC. ex Meisn.
Common Name(s): Devil's claw, Grapple plant, Grapple vine, Radix Harpagophyti, Wood spider, Xwate
Devil's claw grows naturally in the Kalahari Desert and Namibian steppes of southwest Africa. The plant is a weedy perennial bearing small, claw-like protrusions on the fruit and a strong central taproot growing up to 2 m deep. The secondary roots are used in decoctions and teas. The plant's leaves are large and grey-green in color, and it produces pink, red, or purple, trumpet-shaped flowers.1, 2 Devil's claw is also known as Uncaria procumbens and Harpagophytum burchellii Decne.
Devil's claw has been widely used among indigenous people of South Africa as a folk remedy for diseases ranging from liver and kidney disorders to allergies, headaches, and most commonly, rheumatism. Devil's claw was reportedly introduced to Europe by a German soldier in the mid-1900s, and thereafter its popularity increased among British, Canadian, and European herbalists. Devil's claw is marketed in Canada and Europe as a home remedy for the relief of arthritic diseases.1, 2, 3
The major chemical component thought to be responsible for the anti-inflammatory activity of devil's claw is harpagoside, a monoterpene glucoside. Other iridoid glycosides include procumbide, harpagide, 8-para-coumaroyl-harpagide, and verbascoside. Harpagoside is found primarily in the roots; secondary tubers contain twice as much glucoside as the primary roots. Flowers, stems, and ripe fruits are essentially devoid of the compound, while traces have been isolated from the leaves. Harpagoside can be progressively hydrolyzed to harpagid and harpagogenin. Commercial sources of devil's claw extract contain 1.4% to 2% of harpagoside.
Other constituents include carbohydrates, flavonoids (kaempferol, luteolin), aromatic acids, phytosterols, and triterpenes. High-performance liquid chromatography methods for identification have been reported.2, 4, 5
Uses and Pharmacology
In vitro studies are largely supportive of anti-inflammatory action. Mechanisms elucidated include inhibition of COX-2 enzymes and other proinflammatory enzymes, antioxidant activity, reductions in expression of prostaglandin PGE2, and inhibition of cysteinyl-leukotrienes.3, 4, 6, 7, 8, 9
Most animal studies support the anti-inflammatory and analgesic effects of devil's claw extracts. Studies have included oral, intraperitoneal, and intraduodenal routes of administration, with oral use having the most negative findings. Inhibition of carrageenin-induced paw edema by devil's claw was comparable with that of phenylbutazone, indomethacin, and acetyl salicylic acid. A dose-dependent effect has also been described.3, 4, 10, 11, 12, 13, 14
Reviews of clinical trials have focused primarily on arthritic conditions (hip and knee) and low back pain. A meta-analysis of available data has not been conducted, possibly because of diverse methodologies.3, 4, 15, 16, 39
Few quality double-blind, placebo-controlled, or comparator randomized trials have been conducted in osteoarthritis; however, there is general support for evidence of effect in pain reduction. Other clinical studies (open-label) are also supportive. Well-designed, adequately powered studies are required before definitive statements regarding optimal dose, efficacy, and duration of therapy can be made.15, 16 The use of devil's claw in treating low back pain has been reviewed by a Cochrane group who found evidence to support a short-term reduction in pain greater than that of placebo, based on 2 low quality clinical trials.15, 39 Positive results from other less well-designed trials have been published.3, 4
Older animal studies demonstrated cardiac effects of extracts of H. procumbens, including dose-dependent reduction in blood pressure, decreased heart rate, and anti-arrhythmic activity, with mixed results or inotropic and chronotropic effects for different iridoids.17, 18, 19 Clinical studies are lacking.
Central nervous system
A study in rats showed anticonvulsant effects of an extract of H. procumbens, possibly via CNS depression and gamma aminobutyric acid neurotransmission.20 Anticholinesterase activity has also been described.21
Devil's claw has been studied for low back pain, muscle pain, and osteoarthritis using daily doses of crude tuber up to 9 g daily, 1 to 3 g of extract, and harpagoside 50 to 100 mg.3, 22, 23 Commercial preparations are inconsistent in the composition of iridoid glycosides, with some products likely to be more effective than others. Harpagoside is considered the key ingredient for anti-inflammatory effect.23
Devil's claw is not recommended for use in children due to lack of safety or clinical trial data.3 It is also not recommended for long-term use (more than 3 to 4 months) because of a lack of data.3, 24
Pregnancy / Lactation
Avoid use. Oxytocic adverse effects have been documented.2, 3 H. procumbens extract produced rhythmic contractions in isolated rat uterine tissue.25 Case reports indicate the potential to stimulate uterine contractions.26
A poorly documented case report of an interaction with warfarin manifesting as purpura exists.3, 27, 28 However, devil's claw does not affect blood eicosanoid production.29 Use with antiarrhythmic, chronotropic, or inotropic medicines is contraindicated because of decreased heart rate observed in rats and mild positive inotropic effects in rabbits in older studies.3, 18, 19, 30 Devil's claw may also potentiate antidiabetic therapy.2, 3, 4
Based on pharmacologic activity, may alter hemostasis and may be contraindicated in individuals with active bleeding (eg, peptic ulcer, intracranial bleeding). Use with caution in individuals with a history of bleeding, hemostatic disorders, or drug-related hemostatic problems; or in individuals taking anticoagulant medications, including warfarin, aspirin, aspirin-containing products, NSAIDs, or antiplatelet agents (eg, ticlopidine, clopidogrel, dipyridamole).28, 40
Screening studies report that H. procumbens is unable to inhibit cytochrome P450 enzymes and is unlikely to have any clinically relevant effect on the cytochrome system.4, 31 It is possible that devil's claw may affect multidrug P-glycoprotein (P-gp) drug transporter.32
Rare, GI-related adverse effects have been reported in clinical trials, including mild GI upset, anorexia, and loss of taste. Rarely, unspecified serious GI events have been reported. Headache and tinnitus have been reported.33, 34, 38 Cardiovascular adverse events are theoretically possible based on older studies in rodents.34 A case of symptomatic hypertension has been documented in a 62-year-old healthy woman who consumed 500 mg/day of a product containing Devil’s claw. Blood pressure returned to normal and complaints of headache and dizziness subsided in the 2 weeks following discontinuation of the product.37
Anecdotal reports suggest devil's claw may increase stomach pH due to its bitter taste, so it should be avoided in people with gastric or duodenal ulcers.3, 35 Devil's claw should also be used with caution in patients with gallstones.2, 3 Unsubstantiated reports of possible hypoglycemic effects should be considered for diabetic patients.3 Nephrotoxicity is rare, but devil’s claw may impede P-gp excretion of toxins, which could contribute to kidney injury.36
Harpagoside has been found to be of low toxicity, with a median lethal dose of more than 13.5 g/kg in mice. Although no long-term toxicity studies have been reported, rats given oral doses of harpagoside 7.5 g/kg/day showed no clinical, hematologic, or gross pathologic changes.3, 35
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