Berberine (chemical structure left) is an alkaloid present in a number of clinically-important medicinal plants including goldenseal and plants often used to adulterate pure goldenseal such as Coptis chinensis (coptis or goldenthread), Berberis aquifolium (oregon grape), Berberis vulgaris (barberry), and Berberis aristata (tree turmeric).

The alkaloids berberine and hydrastine are commonly used by industry as markers to indicate the quality of raw goldenseal although the most common level of consumer product assurance is that of a specified percentage of total alkaloid content, unspecified as to which alkaloid or how much of each. (Brown 2008, Abourashed, 2001, Govindan, 1999). These two compounds are also thought to be the primary bioactive compounds in the plant.