**2. Herbal medicine**

Natural products chemistry is one of the oldest sciences sought for medicine throughout the history of mankind. Its roots dates back in time, thousands of years ago, through the use of many herbal mixtures as remedies for many diseases. It was clear from the beginning that certain herbs, plants, etc… have certain positive influence when used as remedies for sickness, but it was unclear how the mechanism of remedy was attained. As a consequence of the accumulation of many years of knowledge, traditional medicine has come forth to group, organize and categorize these remedies according to their effects on diseases, whereby, biomedicine and chemistry came to shed more light on the active ingredients of these folk remedies and on the mechanism of their action.

Currently, natural product chemistry has evolved to be an interdisciplinary area of science, concerned with the isolation, characterization and determination of the biological activity of the pure phytochemicals. These active components, generally referred to as secondary metabolites, include phenolics, terpenoids, alkaloids and steroids. Even though it has been proved that many natural products have a strong therapeutic value, limitations related to their poor solubility and bioavailability in addition to toxicity and stability have severely hindered their use as drugs [3]. According to U.S. Food and Drug Administration (FDA), the definition of bioavailability is "the rate and extent to which the active ingredient or active moiety is absorbed from a drug product and becomes available at the site of action" [4].
