Drug Profile

Background

Milk thistle (Silybum marianum) is a plant from the aster or daisy family. Its legend dates back to biblical times; Mary is said to have sheltered Jesus in an arbor of thistle. Ancient Greek and Roman physicians and herbalists extolled its virtues, as did medieval German and 17th-century English herbalists. In the United States, the Eclectics movement, which primarily emphasized Native American herbs, advocated milk thistle for varicose veins, menstrual difficulties, and congestion of the spleen, liver, and kidneys. Over the centuries milk thistle has been recommended for a variety of other maladies, including depression, gallstones, and snakebites.[1]

Herbal products are made from the seeds of the fruit of the plant, which contain bioflavonoids, the most active of which is silybin. Milk thistle is available in a dried form as a capsule and it is also dissolved in alcohol and put into liquid form (tincture of milk thistle). Teas can also be prepared, but little of the putatively active compound dissolves in water.[1]

Claimed Uses

Modern interest in milk thistle has centered on its use for treating various liver diseases. A number of placebo-controlled trials have been conducted. However, many of these trials include patients with a variety of liver ailments and such studies are thus not included in this review. Almost all studies confined their assessments of effectiveness to measuring enzymes present in the liver called aminotransferases; these are frequently elevated in liver illnesses. However, this surrogate for liver health would be insufficient on its own for a drug to receive FDA approval. Instead, studies should focus on improvements in liver biopsies or survival (in conjunction with the amount of virus in the treatment of hepatitis C infection).

Chronic Hepatitis C Infection

Only two randomized, placebo-controlled trials have been conducted. In a 1977 German study (not reviewed directly by us but summarized in a meta-analysis[1]), before hepatitis C had been identified, silymarin, a less active bioflavonoid, was associated with a trend toward improvement in liver biopsy, but this was not evaluated statistically. In the second, which included patients with both hepatitis B and C, some blood tests improved, while others did not; biopsies and mortality were not evaluated.[2] A review of a number of complementary medicines, including milk thistle, for hepatitis C concluded that “There is no firm evidence supporting medicinal herbs for [hepatitis C virus] infection.”[3] The National Center for Complementary and Alternative Medicine has concluded that “The results of scientific studies to date do not definitively find that milk thistle is beneficial in treating hepatitis C in humans.”[4]

Chronic Alcoholic Liver Disease

A review conducted for the Agency for Healthcare Research and Quality identified six placebo-controlled studies of milk thistle. The studies are difficult to interpret due to ongoing alcohol consumption by the patients and due to differences in disease severity. Most of these studies showed improvement in at least one measurement (usually aminotransferases or other blood tests), but more outcomes were unaffected by the treatment and the outcome for which there was apparent effectiveness varied from study to study.[1] Two of these six studies are the only two placebo-controlled trials of milk thistle for alcoholic cirrhosis.

Summarizing the data for alcoholic liver disease as well as for other liver diseases, the Agency for Healthcare Research and Quality concluded: “Clinical efficacy for milk thistle is not clearly established. Interpretation of the evidence is hampered by poor study methods and/or poor quality of reporting in publications. Problems in study design include heterogeneity in etiology and extent of liver disease, small sample sizes, and variation in formulation, dosing, and duration of milk thistle therapy.”[1]

Interactions with Other Drugs

No interactions with other drugs have been reported, but this has not been studied formally.

Adverse Effects

Milk thistle has been generally well tolerated. It has been associated with a laxative effect, nausea, and abdominal discomfort. Milk thistle can also produce allergic reactions in patients allergic to plants in the same family (daisy, ragweed, chrysanthemum, and marigold).[4]

A recent Journal of Parenteral and Enteral Nutrition (JPEN) systematic review revealed that, with a few possible exceptions, dietary supplements offer no benefits to well-nourished adults eating a Western diet and, in many cases, may be harmful. The results of this study reinforce Worst Pills, Best Pills News’ longstanding view that there is little evidence that dietary supplements are either safe or effective.

The study authors concluded that with the possible exception of vitamin D in elderly patients and omega-3 fatty acids in patients with a history of cardiovascular disease, no data support the widespread use of dietary supplements in the U.S. and other Western countries. Indeed, the data suggest that certain commonly used dietary supplements, including beta-carotene, vitamin A and vitamin E, may be harmful. We agree.[5]

Conclusion

While there are a number of placebo-controlled trials of milk thistle in the treatment of various liver diseases, their overall quality is very poor and is not sufficient to support the supplement’s use. The National Center for Complementary and Alternative Medicine is sponsoring a clinical trial of milk thistle in the treatment of hepatitis C. At present, use of the supplement for hepatitis C seems particularly unjustified, given the existence of effective therapies for that condition.[6]