There isn't clear evidence from science that taking milk thistle as a dietary supplement helps with liver problems, such as hepatitis, cirrhosis, and inflammation of the bile ducts (cholangitis).

Milk thistle may cause nausea, diarrhea, bloating, pain, or allergies.

The U.S. Food and Drug Administration (FDA) does not regulate dietary supplements in the same way it regulates medicines. A dietary supplement can be sold with limited or no research on how well it works.

Always tell your doctor if you are using a dietary supplement or if you are thinking about combining a dietary supplement with your conventional medical treatment. It may not be safe to forgo your conventional medical treatment and rely only on a dietary supplement. This is especially important for women who are pregnant or breastfeeding.

When using dietary supplements, keep in mind the following:

• Like conventional medicines, dietary supplements may cause side effects, trigger allergic reactions, or interact with prescription and nonprescription medicines or other supplements you might be taking. A side effect or interaction with another medicine or supplement may make other health conditions worse.
• Dietary supplements may not be standardized in their manufacturing. This means that how well they work or any side effects they cause may differ among brands or even within different lots of the same brand. The form you buy in health food or grocery stores may not be the same as the form used in research.
• Other than in vitamins and minerals, the long-term effects of most dietary supplements are not known.