This section is from the book "Botanic Drugs Their Materia Medica, Pharmacology and Therapeutics", by Thomas S. Blair. Also available from Amazon: Botanic Drugs, Their Materia Medica, Pharmacology and Therapeutics.
Oregon Grape, Mountain Grape, Berberis aqui-folium. Official in U. S. P. Eighth Rev. Berberis Aristata official in England. Berberis vulgaris, Barberry, official in France.
Hydrastis and berberis are allied and will be discussed in detail under "Hydrastis" (q. v.). However, it may be said that Berberine has little action in small doses. In large doses it causes vaso-dilatation and cardiac depression, with reduced blood-pressure. There is no useful field for berberis in large doses. In small doses it is a useful simple bitter. In large doses it is a gastro-intestinal irritant; and alterative properties have been claimed for drugs of that class, but usually upon no secure basis. There is no evidence that berberis possesses alterative properties in doses that are advisable.
In 10- to 30-minim doses fl., is stomachic and of value in atonic dyspepsia. Its astringency, as well as its bitter properties, make its use rational in gastro-intestinal maladies characterized by an excess of mucus. In other words, the bitters - and berberis is a good one - are clinically valuable in slight catarrhal conditions and minor functional disturbances of the alimentary canal; they are not available in the incidence of serious anatomic changes. These bitters are always better taken in liquid form, preferably just before meals.
Berberine Hydrochloride is the alkaloidal representative on the market; it is not made from Berberis aquofilium, but from Berberis vulgaris and Hydrastis Canadensis. Very large doses are toxic; but as much as 20 grains have been taken with little effect except purgation. Dosage ranges from 1 to 5 grains.