Silybum marianum, colloquially identified as Carduus marianus, known as milk thistle, is an annual or biannual plant of the Asteraceae family. This fairly typical thistle has red to purple flowers and shiny pale green leaves with white veins. Originally a native of Southern Europe through to Asia, it is now found throughout the world. The medicinal parts of the plant are the ripe seeds. Common names for this species include blessed milk thistle, Marian Thistle, Mary Thistle, Saint Mary's Thistle, Mediterranean Milk Thistle, Variegated Thistle and Scotch Thistle.
In herbalism, it is used in cases of liver diseases (cirrhosis, jaundice and hepatitis), gallbladder disease, and is claimed to protect the liver against poisons. Silibinin (syn. silybin, sylimarin I) is a hepatoprotective (antihepatotoxic), antioxidant (radical-scavenging agent), thus stabilizing and protecting the membrane lipids of the hepatocytes (liver cells). Silicristin inhibits the enzymes peroxidase and lipoxygenase. Silidianin is a plant growth regulator. A 2000 study of such claims by the AHRQ concluded that "clinical efficacy of milk thistle is not clearly established". However a more recent study did show activity against liver cancer cells in vitro. A 2005 Cochrane Review considered thirteen randomized clinical trials which assessed milk thistle in 915 patients with alcoholic and/or hepatitis B or C virus liver diseases. They question the beneficial effects of milk thistle for patients with alcoholic and/or hepatitis B or C virus liver diseases and highlight the lack of high-quality evidence to support this intervention. Cochrane concluded that more good quality randomized clinical trials on milk thistle versus placebo are needed. Its potent extract is used in medicine under the name silymarin (a flavonolignane complex consisting of silibinin A and B/silybin/silymarin I, isosilibinin A and B, silicristin/silymarin II, silidianin). Silibinin is used against poisoning by amanitas, such as the Death Cap (Amanita phalloides) as well as in cerebral edema and acute hepatitis therapy. Mary thistle has been grown as a medicinal plant in monastery gardens since ancient times. The seed is the part of the plant used medicinally. Silybum marianum extract has antifungal effects, preventing the growth of dermatophyte more than saprophyte fungi. One pilot study showed that milk thistle may be as effective as fluoxetine in treatment of obsessive-compulsive disorder.
It grows 30 to 200 cm tall, having an overall conical shape with a approx. 160 cm max. diameter base. The stem is grooved and more or less cottony, and with the largest specimens the 'trunk' is hollow. The leaves are oblong to lanceolate. They are either lobate or pinnate, with spiny edges. They are hairless, shiny green, with milk-white veins. The flower heads are 4 to 12 cm long and wide, of red-purple colour. They flower from June to August in the North or December to February in the Southern Hemisphere ( Summer through Autumn ). The bracts are hairless, with triangular, spine-edged appendages, tipped with a stout yellow spine. The achenes are black, with a simple long white pappus, surrounded by a yellow basal ring.
Due to potassium nitrate content, the plant has been found to be toxic to cattle and sheep. When potassium nitrate is eaten by ruminants, the bacteria in animal's stomach breaks the chemical down, producing a nitrite ion. Nitrite ion then combines with hemoglobin to produce methaemoglobin, blocking the transport of oxygen. The result is a form of oxygen deprivation.