Does the Synergy Argument in Herbal Medicine Add Up?
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COMMENTARY
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Does the Synergy Argument in Herbal Medicine Add Up? Peter H. Canter Complementary Medicine, Peninsula Medical School, Universities of Exeter & Plymouth, Exeter, UK
Herbal medicines are usually ingested in the form of wholeplant extracts containing many hundreds of different compounds that remain unknown or are only partially characterised regarding type and concentration. Typically, extracts are standardised by controlling the concentrations of one or a few major components. There may be one, or several, known bioactive components but very often the bioactive compounds have not been identified at all. Similarly, while some whole-plant extracts have known toxic components, the concentrations of which are kept within safe limits (e.g. ginkgolic acid in Ginkgo biloba), the partial characterisation of plant extracts means that potentially harmful compounds may remain undetected or occur at unpredictable concentrations.[1] The chemical constitution of plant extracts varies with genetic differences between ecotypes, phenotypic differences arising from different growth environments and seasonal and developmental changes during the life-cycle of the plant.[2] The resulting uncertainty about exactly what is being ingested when a herbal medicine is used is increased further by the possibility of species misidentification,[3,4] contamination or adulteration,[4-6] unreliable standardisation[7] and instability of extracts. The variability in extracts also means that any evidence for efficacy and safety obtained from clinical trials or other scientific studies may be specific to the particular sample tested and may not be generalisable to all extracts from the same species. Indeed, it is not unusual for manufacturers to use this variability as a marketing tool by making specific claims for their particular ecotype or extract. It has been previously argued that one way to reduce these uncertainties and the attendant risks is to bring medicinal plant species into cultivation so that careful control can be exerted over both genotypic and phenotypic variation and potential sources of environmental contamination such as the soil and water.[2] It could also be argued that, instead, we should aim to identify, isolate and purify salient bioactive components in medicinal plant extracts in order to ensure standardisation, optimum therapeutic potency and safety. While in some cases this approach may currently be too expensive or technically impossible, it is unlikely to remain so
with the advances being made in rapid screening of organic compounds, chemical and biological synthesis of target molecules, and the increasingly sophisticated understanding of metabolic pathways and potential drug targets. If it is accepted that these are technical difficulties that will eventually be overcome, then the only remaining justification for continuing to use whole-plant extracts would be that different components present in the extract act synergistically to increase effectiveness o
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