Laboratory studies suggest that milk thistle may benefit the liver by protecting and promoting the growth of liver cells, fighting oxidation (a chemical process that can damage cells), and inhibiting inflammation. Results from clinical trials of milk thistle for liver disease have been mixed, and two rigorously designed studies found no benefit. Reviews of the research have concluded that the efficacy of milk thistle against liver disease has not been established, and additional, high-quality trials are needed.
A 2012 clinical trial, cofunded by NCCAM and the National Institute of Diabetes and Digestive and Kidney Diseases, showed that 2 higher-than-usual doses of silymarin were no better than placebo for chronic hepatitis C in people who had not responded to standard antiviral treatment.
The Hepatitis C Antiviral Long-Term Treatment Against Cirrhosis (HALT) study, sponsored by NIH, found that silymarin use by hepatitis C patients was associated with fewer and milder symptoms of liver disease and somewhat better quality of life, but there was no change in virus activity or liver inflammation.
In clinical trials, milk thistle has appears to be well tolerated for recommended disease treatment. Occasionally, people report various gastrointestinal side effects.
Milk thistle can produce allergic reactions, which tend to be more common among people who are allergic to plants in the same family (for example, ragweed, chrysanthemum, marigold, and daisy).
Milk thistle may lower blood sugar levels. People who have diabetes or hypoglycemia, or who are taking drugs or supplements that affect blood sugar levels, should use caution.
Consult your physician prior to using milk thistle if you are pregnant.
Before taking any new medications, including natural health products, speak to your physician, pharmacist, or other health care provider. Tell your health care provider about any natural health products you may be taking.