The main active ingredient, silymarin, is found in the seeds of this prickly leafed, purple-flowered plant.
Milk thistle is claimed to protect the liver from damage by viruses, toxic substances (such as alcohol and the toxins from death cap mushrooms), and certain drugs (such as acetaminophen). Thus, people take milk thistle to prevent and treat mushroom poisoning and other liver disorders, such as cirrhosis and hepatitis C.
Well-designed scientific studies do not show that milk thistle significantly benefits people with a liver disorder. In reports that have collected information about many individuals with mushroom poisoning, milk thistle reduced the death rate.
Brief stomach upset and mild allergies but no serious side effects have been reported. Milk thistle may intensify the effects of drugs that decrease blood sugar levels (hypoglycemic drugs).
Women who have hormone-sensitive conditions (such as breast, uterine, or ovarian cancer; endometriosis; and uterine fibroids) should avoid the above-ground parts of milk thistle.