Flavonolignans

Silibinin (INN), also known as silybin (both from Silybum, the generic name of the plant from which it is extracted), is the major active constituent of silymarin, a standardized extract of the milk thistle, containing a mixture of flavonolignans consisting of silibinin, isosilibinin, silychristin, silidianin, and others. Silibinin itself is a mixture of two diastereomers, silybin A and silybin B, in approximately equimolar ratio. Silibinin is used in pure forms as a medication, and more frequently as an active ingredient in milk thistle–derived herbal supplements.

Flavonolignans are natural phenols composed of a part flavonoid and a part phenylpropane.