**2. Herbal medicine**

The World Health Organization (WHO) defines herbal medicine as a practice which includes herbs, herbal materials, herbal preparations and finished herbal products, that contain as active ingredients parts of plants, or other plant materials, or combinations [9]. These herbs are derived from plant parts such as leaves, stems, flowers, roots, and seeds [10].

Herbal drugs contain active ingredients, plant parts or plant materials in the processed or crude state with certain excipients, i.e., dilutions, solvents or preservatives [10, 11]. These active ingredients protect plants from damage and diseases and contribute to the plants aroma, flavor and color. Scientifically, they are known as phytochemicals which include several classes such as saponins, flavonoids, glycosides, tannins, alkaloids and terpenoids [12]. Phytochemicals have been scientifically validated over the years to provide health benefits for humans [13]. For example herbal remedies used as sedative and stomachic mixtures contain mainly aromatic plant species which have therapeutic essential oils, possessing antibacterial, stomach-soothing and antispasmodic properties. Plant species which have a high tannin content are used in mixtures for diarrhea and stomach ulcers; generally showing antimicrobials, astringents and anti-inflammatory activities [14, 15]. Bioactive and disease preventing phytochemicals present in medicinal plants are shown in **Table 1**.


**Table 1.** Properties of some major constituents of medicinal plants.
