Milk thistle is a plant named for the white veins on its large prickly leaves.

One of the active ingredients in milk thistle called silymarin is extracted from the plant's seeds. Silymarin is believed to have antioxidant properties.

Milk thistle is sold as an oral capsule, tablet and liquid extract. People mainly use the supplement to treat liver conditions.

Research on milk thistle use for specific conditions shows:

• Diabetes. Milk thistle might lower blood sugar in people who have type 2 diabetes, but more studies are needed to confirm its benefits.
• Indigestion (dyspepsia). Milk thistle, in combination with other supplements, might improve the symptoms of indigestion.
• Liver disease. Research on the effects of milk thistle on liver disease, such as cirrhosis and hepatitis C, has shown mixed results.

Taken in appropriate doses, oral use of milk thistle appears to be safe.

Milk thistle can cause:

• Gastrointestinal issues, such as diarrhea, constipation, nausea, vomiting and abdominal bloating
• Itchiness
• Headache

If you have diabetes, use milk thistle with caution, since the supplement might lower blood sugar. There is also concern that milk thistle might affect estrogen levels. If you have breast cancer, uterine cancer, ovarian cancer, endometriosis or uterine fibroids, consider avoiding milk thistle.

Milk thistle can cause an allergic reaction, including a severe, potentially life-threatening allergic reaction (anaphylaxis). An allergic reaction is more common in people who are allergic to other plants in the Asteraceae family, such as ragweed, daisies, marigolds and chrysanthemums.

Possible interactions include:

• Cytochrome P450 2C9 (CYP2C9) substrates. Taking milk thistle might affect this enzyme and drugs it processes, such as diazepam (Valium), warfarin (Jantoven) and others. This means milk thistle might affect the levels of these drugs in your body.
• Diabetes medications. Milk thistle might lower blood sugar in people who have type 2 diabetes. Closely monitor your blood sugar levels, and talk to your doctor before taking milk thistle supplements if you take diabetes medications.
• Raloxifene (Evista). Milk thistle may affect how your liver processes this osteoporosis medication, causing higher levels of the drug in your bloodstream. Talk to your doctor before taking milk thistle if you're taking raloxifene.
• Simeprevir. Taking milk thistle with this hepatitis C medication might increase levels of the drug in your blood plasma. Avoid using milk thistle and simeprevir together.
• Sirolimus (Rapamune). Taking milk thistle with this immunosuppressant might change the way your body processes the medication.