Overview
The milk thistle plant commonly grows from two to seven 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.
Therapeutic Dosages
The standard dosage of milk thistle is 200 milligrams (mg) two to three times a day of an extract standardized to contain 70 percent silymarin. There is some evidence that silymarin bound to phosphatidylcholine may be better absorbed. This form should betaken at a dosage of 100 to 200 mg twice a day. Considering the severe nature of liver disease, a doctor’s supervision is essential. Also, milk thistle preparations that are designed for oral use should not be injected.
Therapeutic Uses
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. However, silibinin too is, in fact, a mixture,
comprising the two related substances silibinin A and silibinin B. 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. One animal study
suggests that milk thistle can also protect against fetal damage caused by
alcohol.
Silibinin is hypothesized to function by displacing toxins that might bind to the liver, as well as by causing the liver to regenerate more quickly. It may also act as an antioxidant and also stabilize liver cell membranes.
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).
Milk thistle is also used in a vague condition known as minor hepatic
insufficiency, or sluggish liver. This term is mostly used by European physicians
and American naturopathic practitioners (conventional physicians in the
United States do not recognize it). Symptoms are supposed to include aching under
the ribs, fatigue, unhealthy skin appearance, general malaise, constipation,
premenstrual syndrome, chemical sensitivities, and allergies.
One small but apparently well-conducted, double-blind trial found evidence that milk thistle might improve blood sugar control in type 2 diabetes. Milk thistle may also offer some protection to the kidney. Highly preliminary evidence hints that milk thistle might help reduce breast cancer risk. Milk thistle is sometimes recommended for gallstones and psoriasis, but there is little to no evidence that it really helps these conditions.
In one small, placebo-controlled trial, the topical application of milk thistle
with methylsulfonylmethane (MSM) for one month appeared to be
effective in the treatment of forty-six subjects with the skin condition
rosacea.
A small preliminary study investigated whether milk thistle can help to relieve obsessive-compulsive disorder (OCD). Thirty-five adults with OCD were randomized to receive milk thistle (600 mg per day) or the medication fluoxetine (30 mg per day), which is commonly used to treat OCD. At the end of the eight-week trial, researchers did not find any significant differences between the two groups.
Scientific Evidence
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.
Acute viral hepatitis. A twenty-one-day double-blind, placebo-controlled study of 57 people with acute viral hepatitis found significant improvements in the group receiving milk thistle. In another study, 105 people with acute hepatitis receiving milk thistle (140 mg, three times daily) showed modest improvement in some symptoms compared with those taking a placebo for four weeks. On the other hand, a thirty-five-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.
Chronic viral hepatitis. Inconsistent evidence exists regarding whether milk thistle is helpful for chronic viral hepatitis B or C. The herb does not appear to affect levels of virus in the body, but it might help protect the liver from damage and improve some symptoms.
Alcoholic hepatitis. A double-blind, placebo-controlled study performed in 1981 followed 106 Finnish soldiers with alcoholic liver disease over a period of four weeks. 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. However, a three-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. Another study found no benefit in 72 patients followed for fifteen months. It is more effective for people with alcoholism to quit drinking than to continue drinking and take milk thistle.
Liver cirrhosis. A double-blind, placebo-controlled study of 170 people with alcoholic or nonalcoholic cirrhosis found that in the group treated with milk thistle, the four-year survival rate was 58 percent compared with only 38 percent in the placebo group. This difference was statistically significant.
A double-blind, placebo-controlled trial that enrolled 172 people with cirrhosis for four years also found reductions in mortality, but it just missed the conventional cutoff for statistical significance. A two-year double-blind, placebo-controlled study of 200 individuals with alcoholic cirrhosis found no reduction in mortality attributable to the use of milk thistle. However, in a analysis of nineteen randomized trials, researchers concluded that milk thistle was significantly more effective at reducing mortality from liver cirrhosis (mostly alcohol-related) compared with a placebo, but no more effective at reducing mortality from any cause.
Other double-blind studies of people with various forms of cirrhosis have looked at changes in tests of liver function rather than mortality. Some found benefit, while others did not.
Protection from medications that damage the liver. 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). However, according to a twelve-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).
Safety Issues
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. A study of 2,637 participants reported in 1992 showed a low incidence of side effects, limited mainly to mild gastrointestinal disturbance. However, on rare occasions severe abdominal discomfort may occur.
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. However, safety in young children, pregnant or nursing women, and individuals with severe renal disease has not been formally established.
Important Interactions
Milk thistle might have a protective function in persons taking medications that could damage the liver, such as acetaminophen, phenytoin (Dilantin), alcohol, and phenothiazines. 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. This could theoretically reduce the effectiveness of oral contraceptives.
Bibliography
Berardesca, E., et al. “Combined Effects of Silymarin and Methylsulfonylmethane in the Management of Rosacea: Clinical and Instrumental Evaluation.” Journal of Cosmetic Dermatology 7 (2008): 8-14.
El-Kamary, S. S., et al. “A Randomized Controlled Trial to Assess the Safety and Efficacy of Silymarin on Symptoms, Signs and Biomarkers of Acute Hepatitis.” Phytomedicine 16, no. 5 (2009): 391-400.
Huseini, H. F., et al. “The Efficacy of Silybum marianum (L.) Gaertn. (Silymarin) in the Treatment of Type II Diabetes.” Phytotherapy Research 20, no. 12 (2006): 1036-1039.
Hutchinson, C., A. Bomford, and C. A. Geissler. “The Iron-Chelating Potential of Silybin in Patients with Hereditary Haemochromatosis.” European Journal of Clinical Nutrition 64, no. 10 (2010): 1239-1241.
Kroll, D. J., H. S. Shaw, and N. H. Oberlies. “Milk Thistle Nomenclature: Why It Matters in Cancer Research and Pharmacokinetic Studies.” Integrative Cancer Therapies 6 (2007): 110-119.
Rambaldi, A., B. Jacobs, and C. Gluud. “Milk Thistle for Alcoholic and/or Hepatitis B or C Virus Liver Diseases.” Cochrane Database of Systemic Reviews 4 (2007): CD003620.
Saller, R., et al. “An Updated Systematic Review with Meta-analysis for the Clinical Evidence of Silymarin.” Forschende Komplementarmedizine 15 (2008): 9-20.
Sayyah, M., et al. “Comparison of Silybum marianum (L.) Gaertn. with Fluoxetine in the Treatment of Obsessive-Compulsive Disorder.” Progress in Neuro-Psychopharmacology and Biological Psychiatry 34, no. 2 (2010): 362-365.
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