الفهرس 
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Abstract
Herbal medicine is the use of plants, plant parts, their water or solvent extracts, essential oils, gums, resins, exudates or other form of advanced products made from plant parts used therapeutically to provide proactive support of various physiological systems; or, in a more conventional medical sense, to treat, cure, or prevent a disease in animals or human (Weiss, 2000).
Healing with medicinal plant is as old as mankind itself. The connection between man and his search for drugs in nature dates back from the far past, of which there is ample evidence from various sources: written documents, preserved monuments and even original plant medicines. The oldest written evidence of medicinal plants usage for preparation of drugs has been found in a samerian clay slab from Nagpur, approximately 5000 years old, it comprised recipes for drug, some of them alkaloid such as poppy and henbane (Kelly, 2009).Natural products have been an integral part of the ancient traditional medicine systems, e.g. Chinese, Ayurvedic and Egyptian (Sarker and Nahar, 2007).Egyptian papyrus writing describe medicinal uses for plants as early as 3000BC (Rosen,1979).Indigenous cultures such as(African and Native American) used herbs in their healing rituals, while others developed traditional medical system (such as Ayurveda and traditional Chinese medicine) in which herbal therapies were used. In early 19thC, when chemical analysis first become available scientist began to extract and modify the active ingredient from plants, later chemist began making their own version of plant compounds and over time the use of herb medicine declined in favor of drugs. Almost one fourth of pharmaceutical drugs are derived from botanicals. Recently the WHO estimated that 80% of people world wide rely on herbal medicine as primary health care.About 70-80% of the world populations, particularly in the developing countries, rely on non-conventional medicine in their primary healthcare as reported by the WHO (Akerele ,1993) In recent years, there has been growing interest in alternative therapies and the therapeutic use of natural products, especially those derived from plants.This interest in drugs of plant origin is due to several reasons, namely, conventional medicine can be inefficient (e.g. side legal authorities dealing with efficacy and safety procedures, and many published papers point to the lack of quality in the production, trade and prescription of phytomedicinal products.About 25% of the drugs prescribed worldwide come from plants,121 such active compounds being in current use.Of the 252 drugs considered as basic and essential by the WHO, 11% are exclusively of plant origin and asignificant number are synthetic drugs obtained from natural precursors (Rates, 2001).
2.2. African traditional medicine
The WHO estimates that up to 80% of the population in Africa makes use of traditional medicine as well as about 65% of the world’s population (Fabricant and Farnsworth, 2001).African traditional medicine is the oldest and most diverse of all medical systems. In Africa the heads of state and government of the OAU recognized that about 85% of the African population resort to it for their health delivery needs (Okpako, 2006).
2.3. The search of new drugs through ethno medicine
Plants have formed the basis for traditional medicine systems, which have been used for thousands of years in countries such as China (Chang and But, 1986) and India (Kapoor, 1990). Since the WHO estimates that 80% of the world’s inhabitants rely mainly on traditional medicine systems for their health care, plant products have played an important role in health care systems of the remaining 20% of the population and this mainly resides in developed countries. Drugs have been discovered by use of chemical studies which are directed at isolation of active substances from plants used in traditional medicine (Cragg and Newmann, 2005).Traditional system are more culturally acceptable and are able to meet psychological needs in a way western medicine does not.Today the huge traditional knowledge of medicinal plants is playing an important role in the development of new drugs. Africa is considered to bathe cradle with a rich biological and cultural diversity marked regional difference in healing practices (Maydell, 1990).
2.4. Mechanisms of action of bioactive compounds
Two principle mechanisms of action have been proposed for natural antioxidants (Ingold, 1968). The first is a chain-breaking mechanism, by which the primary antioxidant donates an electron to the free radical present in the system (e.g., lipid radical). The second mechanism involves removal of ROS initiators (secondary antioxidants) by quenching chain-initiating catalysis.Alpha-glucosidase inhibitors act by delaying the liberation of D-glucose of oligosaccharides and disaccharides from dietary complex carbohydrates and retard glucose assimilation, reducing postprandial plasma glucose levels (Matsuura et al., 2004). The bioactive compounds may inhibit microorganisms, interfere with some metabolic processes or may modulate gene expression and signal transduction pathways (Kris-Etherton et al., 2002; Manson 2003).Bioactive compounds and essential oils may exhibit different modes.