4.6 Plants as medicines

Plants are already a major source of medicines. In 1990, sales in the USA of prescriptions where material of plant origin was the active ingredient totalled US$141500 million. For many centuries, people around the world have relied on herbal remedies of various kinds in the prevention and cure of ailments and diseases. There are over 211000 medicinal plants named by the World Health Organisation. Although there is some duplication where plants are known by different names in different places, there will be other plants that have not yet found their way on to this list. This is a huge resource, but the value of the majority of these plants has yet to be tested scientifically. One of the cultures where there is a great deal of written information on herbal lore is found within the Indian subcontinent. The Ayurvedic system of medicine traces its written origins back to texts known as the Vedas that were written about 41000 years ago. Ayurveda is a way of life and not just a curative system. Its philosophy embodies an holistic approach to medicine. Diet and behaviour are given equal prominence when health issues are contemplated. The individual is viewed within the framework of society, importance being attached to the well-being of both. Thus, a need for medication is seen as an unfortunate last resort. The theoretical grounding of Ayurvedic medicine is very like Western medicine, in that the principle of homeostasis is very much to the fore. Health is maintained through a dynamic balance of three fundamental elements, a theory that initially sounds alien to Western ears. It turns out that these elements embody the physiological processes as we understand them; they are merely categorized in a different way. Where Ayurveda differs from the Western approach to health is that it has always given the mind, soul and body equal importance. Not only must the body be in physiological balance for health, but it must also be in a healthy balance with mind and soul. The individual's physiological, psychological and religious states must all be in good health because they are inextricably linked. Strict religious codes have ensured that adequate attention is given to hygiene and diet.

Within this tradition, there are around 11,000 plants that have been named and their medicinal properties described. Only now are we beginning to assess the values of these plants in a scientific way. One such study involves collaboration between the Centre for Ageing Research in India and the University of Illinois in the USA. They will clinically test Ayurvedic herbs listed in ancient literature as cures for smritirhransh, the Ayurvedic name for loss of memory. It is thought that this might be Alzheimer's disease, a condition that is causing much concern in India (and elsewhere). In a society that largely lacks benefits such as pensions, individuals must keep working. India has a high population growth rate (2.1% per annum). With a current (1997) population of around 950 million and a projected population of 1680 million by 2050 there is concern about the ability to generate sufficient wealth to maintain current living standards. Alzheimer's is a neurodegenerative disease, the major symptoms of which are loss of memory and altered perception. People with Alzheimer's are not only unable to contribute to the economy, but they also need active nursing. Alzheimer's disease and the very similar senile dementias affect 15% of the population who are over 65 years of age. So the fact that humanity as a whole is ageing, together with India's high population growth rate, make this a particularly urgent area of research for that country. Investigating the properties of traditional remedies has been fruitful in the past, as can be seen in Table 3 below.

Table 3 Some pharmaceuticals derived from plants and fungi.

Drug Use Plant source Plant's native range
bromelain controls tissue inflammation pineapple (Ananas comosus) tropical America
caffeine stimulant, central nervous system tea (Camellia sinensis) South and East Asia
cocaine local anaesthetic coca (Erythroxylon coca) East Andes
codeine, morphine analgesics opium poppy (Papaver somniferum) Western Mediterranean
digitoxin cardiac stimulant foxgloves (Digitalis species) Europe, Mediterranean
diosgenin source of female contraceptive wild yams (Dioscorea species) tropics
L-Dopa Parkinson's disease suppressant velvet bean (Mucuna deeringiana) tropics
gossypol male contraceptive cotton (Gossypium species) warm temperate and topics
Monocrotaline anti-cancer (externally applied) Crotalaria sessiliflora tropics and subtropics
penicillin general antibiotic penicillin fungi (especially Penicillium chrysogenum)
quinine anti-malarial yellow cinchona (Cinchona ledgeriana) Andes to Costa Rica
reserpine reduces high blood pressure Indian snakeroot (Rauvolfia serpentina) Tropics
scopolamine sedative thornapple (Datura metel) South and North America, but widely naturalized
D-tubocurarine active component of curare; surgical muscle relaxant Chondrodendron and Strychnos species Tropics
vinblastine, vincristine anti-cancer, especially childhood leukaemia Madagascar periwinkle (Catharanthus roseus) Madagascar

In addition to the re-discovery of medicinal plants we continue to discover novel compounds from plant sources. The yew, Taxus baccata, has long been used to provide beautiful veneers for high-quality furniture but country people are wary of its leaves because they are extremely poisonous to all livestock. Who would have thought that in the 1990s these same leaves would be used to extract taxol, a powerful new drug used in the treatment of breast and ovarian cancer? What other useful substances lie waiting for us in the familiar plants of the countryside?

The reasons for wishing to preserve biodiversity (species and habitat diversity) are not purely pragmatic. A recent (1995) UK government steering group established the principle that

… we should hand on to the next generation an environment no less rich than the one we ourselves have inherited.

To this end, costed plans were published to reverse the decline of 116 of Britain's fastest disappearing plants and animals. Part of the plan involves the protection of certain habitats such as hedgerows and coastal lagoons. Despite the fact that the World Charter for Nature, adopted by the United Nations in 1982, expressed absolute support for the principle of conserving biodiversity, the UK's plans are the first to be published by any of the countries that signed the UN convention.