It said that one of the major causes of herbal-related adverse events is directly linked to the poor quality of herbal medicines, including raw medicinal plant materials, and to the wrong identification of plant species. Adverse event reports are on the rise, along with use and consumer demand for natural, plant-based remedies.
The industry is currently estimated to be worth more than US$60 billion.
The guidelines also cover protection of biodiversity, currently being debated at a summit in Kuala Lumpur, Malaysia. The boom in herbal medicines threatens to lead to over-harvesting of raw materials, most of which are harvested from the wild and not replaced through sustainable resources.
The European Commission, meeting other parties to the 2002 Biodiversity Convention this week, is hoping to reach agreement on the establishment of a global network of protected areas, indicators to measure biodiversity and strengthening access to genetic resources and equitable sharing of the benefits arising from their use.
Such measures cannot come too soon, according to a report recently published by the UK conservation group Plantlife International. It estimates that some 1300 medicinal plants found in Europe are used commercially, with up to 90 per cent collected from the wild. And at the moment, wasteful harvesting techniques are commonplace.
The WHO guidelines on good agricultural and collection practices (GACP) for medicinal plants list a number of species at risk of being wiped out.
Wild American ginseng, goldenseal, echinacea, black cohosh, slippery elm and kava kava top the 'at-risk list' while the bark from the African tree Pygeum (Prunus africana), a very popular natural remedy for prostate disorders in some European countries such as Spain, is harvested from wild trees growing in the mountain forests of continental Africa and in Madagascar and is unsustainable under current practices.
Devil's Claw, Harpagophytum procumbens, is another popular remedy that is unsustainably harvested and may become extinct in the wild under current practices, says the WHO.
Just under 200 tonnes were exported from Namibia, one of the biggest exporters, between January and August 2000. Between 10,000 and 15,000 harvesters rely on sales from its collection as their only source of cash. However, current prices are not a true reflection of the real value of their work: over the last 24 years the price has dropped by as much as 85 per cent, says the WHO.
But a sustainably harvested Devil's Claw project set up in 1988 on one resettlement farm in Namibia has rapidly expanded, providing local people with a sustainable product at a guaranteed and fair price. This could be the way forward, provided that users of Devil's Claw demand that suppliers stock only certified products.
The guidelines also try to illustrate how inadvertent contamination by microbial or chemical agents during any of the production stages can lead to deterioration in safety and quality. Medicinal plants collected in the wild may be contaminated by other species or plant parts through misidentification, accidental contamination or intentional adulteration, all of which may have unsafe consequences.
A number of adverse event reports have been linked to such practices. Cases of serious cardiac arrhythmias were reported in the USA in 1997 following the accidental substitution of plantain, to be used as a dietary supplement, with Digitalis lanata, generally used for heart conditions. Subsequent investigations were reported to reveal that large quantities of the misidentified plantain had been shipped to more than 150 manufacturers, distributors and retailers over a two-year period.
Fourteen cases of Podophyllum poisoning have been reported from Hong Kong Special Administrative Region of China following the inadvertent use of the roots Podophyllum hexandrum instead of the Gentiana and Clematis species for their antiviral qualities. It is reported that this accidental substitution arose because of the apparent similarity in the morphology of the roots.
The guidelines can be obtained from the WHO website.