The major active constituent is considered to be the bitter iridoid glucoside, harpagoside, which should constitute not less than 1.2% of the dried herb. Other iridoid glycosides include harpagide and procumbide. About 50% of the herb consists of sugars. There are also triterpenes, phytosterols, plant phenolic acids, flavonol glycosides and phenolic glycosides. Harpagophytum zeyheri, which has a lower level of active compounds, may be partially substituted for H. procumbens in some commercial preparations (Stewart & Cole 2005). The extraction solvent (e.g. water, ethanol) has a major impact on the active principle of the products (Chrubasik 2004a)
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