The milk thistle plant commonly grows from 2 to 7 feet in height, with spiny leaves and reddish-purple, thistle-shaped flowers. It has also been called wild artichoke, holy thistle, and Mary thistle. Native to Europe, milk thistle has a long history of use as both a food and a medicine. At the turn of the twentieth century, English gardeners grew milk thistle to use its leaves like lettuce (after cutting off the spines), the stalks like asparagus, the roasted seeds like coffee, and the roots (soaked overnight) like oyster plant. The seeds and leaves of milk thistle were used for medicinal purposes as well, such as treating jaundice and increasing breast milk production.
German researchers in the 1960s were sufficiently impressed with the history and clinical effectiveness of milk thistle to begin examining it for active constituents. In 1986, Germany's Commission E approved an oral extract of milk thistle as a treatment for liver disease. However, the evidence that it really works remains incomplete and inconsistent.
Based on the extensive folk use of milk thistle in cases of jaundice, European medical researchers began to investigate its medicinal effects. It is currently used to treat alcoholic hepatitis, liver cirrhosis, liver poisoning, and viral hepatitis, as well as to protect the liver in general from the effects of liver-toxic medications. However, despite this wide usage, there is no definitive evidence that it is effective.
Standardized milk thistle extract is known as silymarin. Silymarin itself is a mixture of at least seven chemicals. The most active of these chemicals is commonly known as silibinin. But, silibinin too is, in fact, a mixture, comprising the two related substances silibinin A and silibinin B.48 When injected intravenously, silibinin is thought to act as an antidote to poisoning by the deathcap mushroom, Amanita phalloides. Animal studies suggest that milk thistle extracts can also protect against many other poisonous substances, from toluene to the drug acetaminophen.2-7 One animal study suggests that milk thistle can also protect against fetal damage caused by alcohol.8
Silibinin is hypothesized to function by displacing toxins trying to bind to the liver as well as by causing the liver to regenerate more quickly.9 It may also act as an antioxidant and also stabilize liver cell membranes.10,11
In Europe, milk thistle is often added as extra protection when patients are given medications known to cause liver problems. However, milk thistle failed to prove effective for preventing liver inflammation caused by the Alzheimer's drug Cognex (tacrine).12
Milk thistle is also used in a vague condition known as minor hepatic insufficiency, or "sluggish liver."13 This term is mostly used by European physicians and American naturopathic practitioners—conventional physicians in the US don't recognize it. Symptoms are supposed to include aching under the ribs, fatigue, unhealthy skin appearance, general malaise, constipation, premenstrual syndrome, chemical sensitivities, and allergies.
Milk thistle may also offer some protection to the kidney.14
Highly preliminary evidence hints that milk thistle might help reduce breast cancer risk.15 Other even more preliminary studies have suggested potential benefits in slowing cancer growth in a variety of cancers including colon, breast, ovarian, skin, and liver cancers.56,57,58,59 Unfortunately, these trials were done on cancer cells cultivated in a lab or animal studies so benefit in a human body is not understood. Human clinical studies will need to be done to help determine the benefits of milk thistle, potential side effects on the body, impact on cancer treatment, and proper dosing.
In one small, placebo-controlled trial, the topical application of milk thistle with methylsulfonylmethane (MSM) for 1 month appeared to be effective in the treatment of 46 subjects with the skin condition rosacea.50
A small preliminary study investigated whether milk thistle can help to relieve obsessive compulsive disorder (OCD).52 Thirty-five adults with OCD were randomized to receive milk thistle (600 mg/day) or the medication fluoxetine (30 mg/day), which is commonly used to treat OCD. At the end of the 8-week trial, researchers did not find any significant differences between the two groups.
As noted above, there is considerable evidence from studies in animals that milk thistle can protect the liver from numerous toxins. However, human studies of people suffering from various liver diseases have often yielded mixed results. A 2007 review of published and unpublished studies on milk thistle as a treatment for liver disease caused by alcohol or viral hepatitis concluded that benefits were seen only in low-quality trials, and, even in those, milk thistle did not show more than a slight benefit.49
A 21-day, double-blind, placebo-controlled study of 57 people with acute viral hepatitis found significant improvements in the group receiving milk thistle.20 In another study, 105 people with acute hepatitis receiving milk thistle (140 mg, 3 times daily) showed modest improvement in some symptoms compared to those taking a placebo for 4 weeks.53 On the other hand, a 35-day study of 151 individuals thought to have acute hepatitis found no benefit with milk thistle, but this study has been criticized for failing to document that the participants actually had acute hepatitis.21,22
Inconsistent evidence exists regarding whether milk thistle is helpful for chronic viral hepatitis B or C.17-19,44,46,51 The herb does not appear to affect levels of virus in the body, but might help protect the liver from damage and improve some symptoms.
A double-blind, placebo-controlled study performed in 1981 followed 106 Finnish soldiers with alcoholic liver disease over a period of 4 weeks.23 The treated group showed a significant decrease in elevated liver enzymes and improvement in liver histology (the microscopic structure of liver tissue), as evaluated by biopsy in 29 subjects.
Two similar studies provided essentially equivalent results.24,25 However, a 3-month, randomized, double-blind study of 116 people showed little to no additional benefit, perhaps because most participants reduced their alcohol consumption and almost half stopped drinking entirely.26 Another study found no benefit in 72 patients followed for 15 months.27 It is undoubtedly more effective for people with alcoholism to quit drinking than to continue drinking and take milk thistle!
A double-blind, placebo-controlled study of 170 people with alcoholic or non-alcoholic cirrhosis found that in the group treated with milk thistle the 4-year survival rate was 58% as compared to only 38% in the placebo group.28 This difference was statistically significant.
A double-blind, placebo-controlled trial that enrolled 172 people with cirrhosis for 4 years also found reductions in mortality, but they just missed the conventional cutoff for statistical significance.29 A 2-year, double-blind, placebo-controlled study of 200 individuals with alcoholic cirrhosis found no reduction in mortality attributable to the use of milk thistle.30 However, in a analysis of 19 randomized trials, researchers concluded that milk thistle was significantly more effective at reducing mortality from liver cirrhosis (mostly alcohol-related) compared to placebo, but no more effective at reducing mortality from any cause.51
Numerous medications can injure or inflame the liver. Preliminary evidence suggests that milk thistle might protect against liver toxicity caused by drugs such as acetaminophen, alcohol, phenothiazines, and phenytoin ( Dilantin).31,32 However, according to a 12-week, double-blind study of 222 people, milk thistle does not seem to prevent the liver inflammation caused by the Alzheimer's drug tacrine (Cognex).33
Chemotherapy is not only toxic to cancer but also toxic to healthy cells throughout the body especially the liver. Milk thistle showed some protective benefit on the liver during aggressive chemotherapy in one randomized trial of children with leukemia. There was a trend for higher chemotherapy doses needed in children taking milk thistle but the trend was not statistically significant.56
The standard dosage of milk thistle is 200 mg 2 to 3 times a day of an extract standardized to contain 70% silymarin.
There is some evidence that silymarin bound to phosphatidylcholine may be better absorbed.34,35 This form should be taken at a dosage of 100 mg to 200 mg twice a day.
Warning: Considering the severe nature of liver disease, a doctor's supervision is essential. Also, do not inject milk thistle preparations that are designed for oral use!
Milk thistle is believed to possess very little toxicity. Animal studies have not shown any negative effects even when high doses were administered over a long period of time.36
A study of 2,637 participants reported in 1992 showed a low incidence of side effects, limited mainly to mild gastrointestinal disturbance.37 However, on rare occasions severe abdominal discomfort may occur.38
On the basis of its extensive use as a food, milk thistle is believed to be safe for pregnant or nursing women and researchers have enrolled pregnant women in studies.39 However, safety in young children, pregnant or nursing women, and individuals with severe renal disease has not been formally established.
No drug interactions are known. However, one report has noted that silibinin can inhibit a bacterial enzyme called beta-glucuronidase, which plays a role in the activity of certain drugs, such as oral contraceptives.40 This could theoretically reduce their effectiveness.
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Last reviewed December 2015 by EBSCO CAM Review Board Last Updated: 12/15/2015