Milk thistle is a member of the aster family that is native to
southern Europe and Asia and now naturalized throughout much of the
world. Like most thistles, milk thistle is characterized by sharp spines
or thorns that surround the flower head. The herb is grown as an
ornamental specimen as well as a commercial crop. Although other parts
of the plant may be used, milk thistle is primarily cultivated and
harvested for its seeds.
Milk thistle seeds contain several active chemicals, including a group
of closely related flavonolignans. Collectively known as silymarin, the
group consists of silybin A, silybin B, isosilybin A, isosilybin B,
silychristin, isosilychristin and silydianin. The raw seeds contain
about 6% of this flavonolignan complex, while the liquid extract
prepared from the seeds contains as much as 80%.
