An isoquinoline alkaloid. Molecular formula [C20H18NO4]+. Also known as berberine. Exist in many plants of 4 families and 10 genera such as Berberiaceae. Berberine can precipitate yellow needle-like crystals from ether. Melting point 145°C. It is soluble in water, hardly soluble in benzene,Berberine is a quaternary ammonium alkaloid, and the solubility of its salts in water is relatively small. For example, the hydrochloride is 1:500 and the sulfate is 1:30. The crystals of berberine precipitated from water or dilute ethanol have 5.5 molecules of crystal water; if it is crystallized it also has corresponding crystal solvent molecules. Berberine is treated with different alkalis to obtain three different forms of berberine in quaternary ammonium form, aldehyde form and alcohol form, among which the quaternary ammonium form is the most stable. Berberine has antibacterial effects on hemolytic Streptococcus, Staphylococcus aureus, Neisseria gonorrhoeae, Freund and Shigella dysentery, and has the effect of enhancing the phagocytosis of leukocytes. Berberine hydrochloride (commonly known as berberine hydrochloride) has been widely used in the treatment of gastroenteritis, bacillary dysentery, etc. It also has certain effects on tuberculosis, scarlet fever, acute tonsillitis and respiratory infections.