Through the ages, the thistle has earned a reputation as a cursed plant. Bristly and prickly, it spreads rapidly and can take over vast fields where less invasive plants once stood. Ancient people often considered the thistle an abomination, a sign of a rich land gone wrong. Even today, if you choose to grow thistle in your garden, neighbors may turn against you if the flower head goes to seed.
Such factors could overshadow the thistle’s therapeutic assets. But modern research shows that the fruit of the milk thistle (Silybum marianum) may restore and protect the liver, the body’s largest internal organ, from damage by chemicals, alcohol, and other toxins.
Historical references to the thistle’s medicinal value, including liver protection, are particularly abundant in the herbals of the Middle Ages. But milk thistle has been praised throughout the centuries for its ability to cure; such observations have contributed to modern interest in the herb.
Dioscorides, the first-century Greek physician who wrote a treatise on more than 600 medicinal plants titled De Materia Medica, stated that a tea of thistle seeds could be used for treating snakebite. John Gerard, a sixteenth-century English herbalist, went further. “My opinion,” he wrote, “is that this is the best remedy that grows, against all melancholy diseases.” Melancholy once referred to any liver or bile disease; it comes from the Greek roots melan, for black, and chole¯, for bile.
Nicholas Culpeper, a seventeenth-century apothecary, thought milk thistle was good for removing obstructions of the liver and spleen, and recommended an infusion of the fresh root and seeds to treat jaundice. The Eclectics, a school of medical herbalists of the late nineteenth and early twentieth centuries, used milk thistle to treat varicose veins and various pelvic congestions, including those linked to menstruation and to the liver, spleen, and kidneys.
Using milk thistle as medicine became less common in the West during the twentieth century, perhaps with the discovery of penicillin and the development of modern medical approaches. But during the 1970s in Germany, where herbs have remained an integral part of medical care, scientists began testing the herb’s fruits (commonly referred to as seeds) and discovered some compounds collectively called silymarin.
During the 1980s, researchers learned that silymarin increases the ability of liver cells to regenerate through a vital bodily process known as protein synthesis. Additionally, laboratory and human research showed that silymarin counteracts the effects of poisons, even that from the deathcap mushroom (Amanita phalloides), the most virulent liver toxin known.
Few plant principles have been more extensively researched than silymarin. More than 300 laboratory and human trials have proven that there is strong scientific basis for believing that it can protect the liver from damage by toxins such as carbon tetrachloride and alcohol while showing no toxic effects against the human body. Such results have convinced German health officials to recognize silymarin as helpful in treating hepatitis, cirrhoisis, and other chronic inflammatory liver disorders.
Many studies have focused on the deathcap mushroom, whose species include those that contain phalloidine, the quickest-acting and most toxic of liver poisons. Phalloidine destroys the outer membrane of liver cells, a situation that can lead to death within three to seven days of ingestion. Another deathcap mushroom toxin, alpha-amanatine, penetrates the cell nucleus to block normal cell regeneration, resulting in the breakdown of the liver, entry of waste products into the bloodstream, and death after three to five days.
One early study (1983) of eighteen patients suffering from poisoning after eating deathcap mushrooms showed that silymarin, taken at a daily dose of 33 mg for every kilogram of body weight for 81.6 hours, prevented severe liver damage. Researchers concluded that silymarin is an effective remedy if administered within 48 hours after eating the mushrooms. Further studies indicated that silymarin works against phalloidine by occupying its binding sites so that it can’t destroy cell membranes, and works against alpha-amanatine by changing the outer cell membrane so the toxin can’t permeate it. Specifically, silymarin stimulates RNA polymerase A, which, in turn, enhances protein synthesis and liver cells’ ability to rebuild themselves, an effective defense against not only deathcap mushroom poisoning but also industrial chemical and alcohol-induced poisoning. A 1988 study, for example, focused on thirty workers who had been exposed to toluene and/or xylene vapors on the job for five to twenty years. All the workers had low blood platelet counts and abnormal liver function tests. After taking silymarin for thirty days, researchers reported, the workers all showed a significant improvement in liver function tests and blood platelet counts, although dosages weren’t specified in the study’s translation.
Further, some researchers have concluded that silymarin may be an effective preventive medicine. It offers valuable liver protection from exposure to alcohol, industrial chemicals, and psychopharmaceuticals because it speeds up the liver’s ability to return to normal. Additionally, the standardized seed preparations alter the cell structure of the outer liver membrane so toxins can’t enter the organ in the first place.
Researchers working primarily for phytopharmaceutical companies continue to aim for a precise understanding of how silymarin works. Among the pieces of the puzzle they have so far are, first, that silybin, one member of the group of compounds that make up silymarin, contains a steroid structure. Steroids enter cells to stimulate protein synthesis and cell regeneration, so silybin’s steroidal activity may be the mechanism by which silymarin works.
Additionally, researchers know that silymarin acts almost solely on the liver and kidneys, possibly because it moves in a rigid cycle from blood plasma to the liver bile and so is concentrated in liver cells. This cycle is difficult to break, one reason why some toxic substances are so destructive—they also concentrate in the liver. Toxins allow waste products to enter the bloodstream by impairing the liver’s ability to transform them into water-soluble compounds, which pass harmlessly from the body through the kidneys and urine. Silymarin, which moves along the same path but is both nontoxic and therapeutic, counteracts this destructive activity, making it one of the liver’s best allies.
Finally, research shows that silymarin is a powerful antioxidant that focuses its power directly on the liver, protecting it against cell-damaging free radicals.
Christopher Hobbs, a member of the Herbs for Health Editorial Advisory Board, is a fourth-generation herbalist and botanist who has been a consultant to the herb industry since 1985. A revised edition of his book, Milk Thistle: The Liver Herb (Botanica, 1995), is due out from Interweave this fall.
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