An herbal medicinal drug may be a single active constituent or an entire herb source and is considered to be a medicinal product. Stability testing of herbal products is a complicated issue because the entire herb or herbal product is regarded as the active substance, regardless of whether the constituents with defined therapeutic activity are known. Stability studies should be performed on at least three production batches of the herbal products for the proposed shelf life, which is normally denoted as long term stability and is performed under natural atmospheric conditions. Markers are chemically known compounds which may or may not have therapeutic effect, which are used to calculate the quantity of herbal medicinal ingredients in herbal medicinal products. According to World Health Organization guidelines, the physical and chemical stability of a product in the container in which it is to be marketed should be tested under defined storage conditions and the shelf life should be established.