Milk thistle is a common plant that has long been regarded useful for protecting the liver; many take it to fight chronic hepatitis or cirrhosis.  A lot of people also take milk thistle simply to “de-toxify” and keep their liver healthy. But how well does it really work?

As usual with herbal supplements, evidence-based data can be hard to find. But there are a few organizations and websites dedicated to evidence-based research, including the Cochrane Collaboration as well as the US NIH National Center for Complementary and Alternative Medicine (NCCAM). The NCCAM has a nice summary page of milk thistle, including their summary:

What the Science Says

There have been some studies of milk thistle on liver disease in humans, but these have been small. Some promising data have been reported, but study results at this time are mixed.

Although some studies conducted outside the United States support claims of oral milk thistle to improve liver function, there have been flaws in study design and reporting. To date, there is no conclusive evidence to prove its claimed uses.

Recent NCCAM-funded research includes a phase II study to better understand the use of milk thistle for chronic hepatitis C. Additional research, cofunded by NCCAM and the National Institute of Diabetes and Digestive and Kidney Diseases, includes studies of milk thistle for chronic hepatitis C and nonalcoholic steatohepatitis (liver disease that occurs in people who drink little or no alcohol).

The National Cancer Institute and the National Institute of Nursing Research are also studying milk thistle, for cancer prevention and to treat complications in HIV patients.

The wonderful Cochrane Collaboration also did a large review of milk thistle’s effectiveness with hepatitis B and C patients and found “no evidence supporting or refuting milk thistle for alcoholic and/or hepatitis B or C virus liver diseases.” Here’s their synopsis:

Milk thistle (Silybum marianum (L) Gaertneri) extracts have been used as medical remedies since the time of ancient Greece. Alcohol and hepatotoxic viruses are the major causes of liver diseases. Several trials have studied the effects of milk thistle for patients with liver diseases. This systematic review could not demonstrate significant effects of milk thistle on mortality or complications of liver diseases in patients with alcoholic and/or hepatitis B or C liver diseases combining all trials or high-quality trials. Low-quality trials suggested beneficial effects. High-quality randomised clinical trials on milk thistle versus placebo are needed.

The Bottom Line?

There doesn’t seem to be any strong evidence that healthy persons should take this as a daily supplement to keep their liver healthy. Some other studies with liver disease patients show slight benefit, but as pointed out above, those studies generally were not well designed and therefore cannot be used as proof. Hopefully, better studies will soon show some effectiveness. And at least there doesn’t seem to be any major side effect in taking it.

The New York Times also has a nice summary (Really? – The Claim – Milk Thistle Is Good for the Liver – Question – NYTimes.com).