A medicinal plant is any plant which, in one or more of its organs, contains substances that can be used for therapeutic purposes, or which are precursors for chemo-pharmaceutical semi-synthesis. When a plant is designated as ‘medicinal’, it is implied that the said plant is useful as a drug or therapeutic agent or an active ingredient of a medicinal preparation. Medicinal plants may therefore be defined as a group of plants that possess some special properties or virtues that qualify them as articles of drugs and therapeutic agents, and are used for medicinal purposes.
History of Plant Based Traditional Medicine
Plants have formed the basis of sophisticated traditional medicine (TM) practices that have been used for thousands of years by people in China, India, and many other countries. Some of the earliest records of the usage of plants as drugs are found in the Artharvaveda, which is the basis for Ayurvedic medicine in India (dating back to 2000 BCE), the clay tablets in Mesopotamia (1700 BCE), and the Eber Papyrus in Egypt (1550 BCE). Other famous literature sources on medicinal plant include “De Materia Medica,” written by Dioscorides between CE 60 and 78, and “Pen Ts’ao Ching Classic of Materia Medica” (written around 200 CE).
Nowadays plants are still important sources of medicines, especially in developing countries that still use plant-based TM for their healthcare. In 1985, it was estimated in the Bulletin of the World Health Organization (WHO) that around 80 % of the world’s population relied on medicinal plants as their primary healthcare source. Even though a more recent figure is not available, the WHO has estimated that up to 80 % of the population in Africa and the majority of the populations in Asia and Latin America still use TM for their primary healthcare needs. In industrialized countries, plant-based traditional medicines or phytotherapeuticals are often termed complementary or alternative medicine (CAM), and their use has increased steadily over the last 10 years. In the USA alone, the total estimated “herbal” sales for 2005 was $4.4 billion, a significant increase from $2.5 billion in 1995. However, such “botanical dietary supplements” are regulated as foods rather than drugs by the United States Food and Drug Administration (US FDA).
Role of Plants in Human History
Plants have also been used in the production of stimulant beverages (e.g. tea, coffee, cocoa, and cola) and inebriants or intoxicants (e.g., wine, beer, kava) in many cultures since ancient times, and this trend continues till today. Tea (Camellia sinensis Kuntze) was first consumed in ancient China (the earliest reference is around CE 350), while coffee (Coffea arabica L.) was initially cultivated in Yemen for commercial purposes in the 9th century. The Aztec nobility used to consume bitter beverages containing raw cocoa beans (Theobroma cacao L.), red peppers, and various herbs. Nowadays, tea, coffee, and cocoa are important commodities and their consumption has spread worldwide. The active components of these stimulants are methylated xanthine derivatives, namely caffeine, theophylline, and theobromine, which are the main constituents of coffee, tea, and cocoa, respectively.
The most popular inebriants in society today are wine, beer, and liquor made from the fermentation of fruits and cereals. Wine was first fermented about 6000–8000 years ago in the Middle East, while the first beer was brewed around 5000–6000 BCE by the Babylonians. The intoxicating ingredient of these drinks is ethanol, a by-product of bacterial fermentation, rather than secondary plant metabolites. Recent studies have shown that a low to moderate consumption of red wine is associated with reduction of mortality due to cardiovascular disease and cancer.
Examples of Some Modern Medicine Discovered from Plants
Plants can provide biologically active molecules and lead structures for the development of modified derivatives with enhanced activity and reduced toxicity. The small fraction of flowering plants that have so far been investigated have yielded about 120 therapeutic agents of known structure from about 90 species of plants. Some of the useful plant drugs include vinblastine, vincristine, taxol, podophyllotoxin, camptothecin, digitoxigenin, gitoxigenin, digoxigenin, tubocurarine, morphine, codeine, aspirin, atropine, pilocarpine, capscicine, allicin, curcumin, artemesinin and ephedrine among others. In some cases, the crude extract of medicinal plants may be used as medicaments. About 121 (45 tropical and 76 subtropical) major plant drugs have been identified for which no synthetic one is currently available.
It has been estimated that more than 400 traditional plants or plant-derived products have been used for the management of type 2 diabetes across geographically. Galegine, a substance produced by the herb Galega officinalis, provides an excellent example of such a discovery. Experimental and clinical evaluations of galegine, provided the pharmacological and chemical basis for the discovery of metformin which is the foundation therapy for type 2 diabetes.
Plant derived agents are also being used for the treatment of cancer. Several anticancer agents including taxol, vinblastine, vincristine, the camptothecin derivatives, topotecan and irinotecan, and etoposide derived from epipodophyllotoxin are in clinical use all over the world.
In conclusion, plants have provided humans with many of their essential needs, including life-saving pharmaceutical agents. Recently the World Health Organization estimated that 80% people worldwide rely on herbal medicines for some aspect. Many developing countries have intensified their efforts in documenting the ethnomedical data and scientific research on medicinal plants. Natural products or natural product derivatives comprised 14 of the top 35 drugs in 2000 based on worldwide sales. There are more than 270,000 higher plants existing on this planet. But only a small portion has been explored phytochemically. So, it is anticipated that plants can provide potential bioactive compounds for the development of new ‘leads’ to combat various diseases. As a vast proportion of the available higher plant species have not yet been screened for biologically active compounds, drug discovery from plants should remain an essential component in the search for new medicines & the scientific study of traditional medicines, concerned medicinal plants are thus of great importance.
Bailey, C.J. and Day, C. (1989) Traditional plant medicines as treatments for diabetes. Diabetes Care, 12 American diabetes association,553–564.
Butlet MS. The role of natural product chemistry in drug discovery. J Nat Prod. 2004; 67: 2141-53.
K.G. Ramawat and J.M. Mérillon, Bioactive Molecules and Medicinal Plants, Springer-Verlag Berlin Heidelberg 2008, ISBN 978-3-540-74600-3.
Kumar, N., M. Abdul Khader, J. B. M., Rangaswami, P. and Irulappan, I. 1997. Introduction to Spices, Plantation Crops, Medicinal and Aromatic Plants. Oxford and IBH Publishing Co. Pvt. Ltd., New Delhi.
Kumar, S., Shukla, Y. N., Lavania, U. C., Sharma, A. and Singh, A. K. 1997. Medicinal and Aromatic Plants: Prospects for India. J. Med. Arom. Pl. Sc. 19 (2):361-365.
P. P. Joy, J. Thomas, S. Mathew, B. P. Skaria, 1998. Medicinal plants, Kerala Agricultural University, Aromatic and Medicinal Plants Research Station.