Milk thistle is a plant named for the white veins on its large prickly leaves.
One of the active ingredients in milk thistle is silymarin, which is extracted from the plant's seeds. Silymarin is a flavonoid believed to have antioxidant properties.
Milk thistle is sold as an oral capsule, tablet, powder 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.
- 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.
Milk thistle appears to be safe when taken in appropriate doses and might play a role in treating certain liver conditions.
Safety and side effects
Taken in appropriate doses, oral use of milk thistle appears to be safe.
Milk thistle can cause:
- Gastrointestinal issues
If you have diabetes, use milk thistle with caution, since the supplement might lower blood sugar. There is also concern that milk thistle might have estrogenic effects. 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 (Coumadin, Jantoven) and others.
- Diabetes medications. Milk thistle might lower blood sugar in people who have type 2 diabetes. Taking milk thistle with diabetes drugs might cause additive effects. Closely monitor your blood sugar levels.
- Metronidazole (Flagyl). Milk thistle might reduce the effectiveness of this antibiotic. Avoid using milk thistle and metronidazole together.
- Simeprevir (Olysio). Taking milk thistle with this hepatitis C medication might increase the concentrations 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.