WHO has published guidelines for good agricultural and collection practices for medicinal plants intended for national governments, to ensure production of herbal medicines is of good quality, safe, sustainable and poses no threat to people or the environment.
Herbal medicines are the natural answer to many ailments and are often locally available. For this reason, their use remains widespread and they are popular in many countries. Because of improved monitoring, reports of patients experiencing adverse reactions with use of herbal medicines are on the rise. Major causes of adverse events can be directly linked to poor quality, particularly of raw medicinal plant materials, or to the wrong identification of plant species. Cultivating, collecting and classifying plants correctly is therefore important.
In addition to patient safety issues, there is the risk that a growing herbal market might pose a threat to biodiversity through over-harvesting of raw materials needed in herbal and traditional medicines and other natural health care products. If not controlled, these practices may lead to the extinction of endangered species and the destruction of natural habitats and resources.
The WHO guidelines on good agricultural and collection practices (GACP) for medicinal plants are an important initial step to ensuring provision of good quality, safe herbal medicines and ecologically sound cultivation practices for future generations. The Guidelines cover the spectrum of cultivation and collection activities, including site selection, climate and soil considerations and identification of seeds and plants. Guidance is also given on the main post-harvest operations and includes legal issues such as national and regional laws on quality standards, patent status and benefit sharing.
The safety and quality of raw medicinal plant materials and finished products depend on genetic or external factors, including environment, collection methods, cultivation, harvest, postharvest processing, transport and storage practices. Inadvertent contamination by microbial or chemical agents during any of the production stages can also 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. Examples of this are:
Digitalis: Cases of serious cardiac arrhythmias were reported in the USA in 1997 following the accidental substitution of plantain as a dietary supplement with Digitalis lanata, generally used for heart conditions. Subsequent investigations revealed that large quantities of mislabelled plantain had been shipped to more than 150 manufacturers, distributors and retailers over a two-year period.
Podophyllum: Fourteen cases of Podophyllum poisoning were reported from Hong Kong, China following the inadvertent use of Podophyllum hexandrum root instead of Gentiana and Clematis species, for their antiviral qualities. This accidental substitution arose through the apparent similarity in morphology of the root.
Aconitum: Cases of cardiotoxicity resulting from the ingestion of Aconitum species used in complementary medicine for acute infections and panic attacks have been reported. Aconitum rootstocks are processed by soaking or boiling in water to hydrolyse the aconite alkaloids into a less toxic, aconine derivative. Toxicity can result when such processes are mismanaged. In the United Kingdom, the internal use of aconite is restricted to prescription only.
Endangered medicinal plants
The wild type of ginseng (Panax ginseng), used to address digestive conditions resulting from nervous disorders, is currently reported to be rapidly declining due to increasing demand and collection. While wild American ginseng, goldenseal, echinacea, black cohosh, slippery elm and kava kava top the “at-risk list” of endangered species of medicinal plants.
Cultivation has replaced wild collection for the supply of some essential drugs used in modern medicine. The Madagascar rosy periwinkle, Catharanthus roseus, is widely cultivated in Spain and the United States for its properties for treating childhood leukaemia and Hodgkin disease.
Demand is also greater than supply for the bark of Pygeum (Prunus africana), a popular natural remedy for prostate disorders in European countries which is harvested from wild trees growing in the mountain forests of continental Africa and Madagascar. Demand is currently unsustainable.
Devil’s Claw (Harpagophytum procumbens) is also unsustainably harvested and may become extinct in the wild under current practices. It is used as a tonic, treatment for arthritis and rheumatism, to reduce fever, ease sore muscles, reduce cholesterol, and externally the ointment is used to treat sores, boils, and ulcers. It is also used to cleanse the lymphatic system, and to remove toxins from the blood.
Reference: WHO Note for the Press No. 3,10 February 2004