Health Guide

Milk thistle

What is it?

Milk thistle is an herbal medicine used to treat liver problems and protect the liver and kidneys.

Other names for milk thistle include: silymarin, bull thistle, holy thistle, lady's thistle, St. Mary's thistle, and cardo blanco.

Ask your doctor, nurse, or pharmacist if you need more information about this medicine or if any information in this leaflet concerns you.

Before Using:

Tell your doctor if you ...

  • are taking medicine or are allergic to any medicine (prescription or over-the-counter (OTC) or dietary supplement).
  • are allergic to plants in the Asteraceae or Compositae family (examples: daisy, thistle, sunflower).
  • are pregnant or plan to become pregnant while using this medicine.
  • are breastfeeding.
  • have any other health problems, such as high blood pressure or heart or blood vessel disease.


Talk with your caregiver about how much milk thistle you should take. The amount depends on the strength of the medicine and the reason you are taking milk thistle. If you are using this medicine without instructions from your caregiver, follow the directions on the medicine bottle. Do not take more medicine or take it more often than the directions tell you to

To store this medicine:

Keep all medicine locked up and away from children. Store medicine away from heat and direct light. Do not store your medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down and not work the way it should work. Throw away medicine that is out of date or that you do not need. Never share your medicine with others.

Drug and Food Interactions:

Do not take milk thistle without talking to your doctor first if you are taking:

  • Medicines to treat infection (examples: metronidazole, (Flagyl(R), MetroGel(R)) (4)


  • Before taking milk thistle, tell your doctor if you are pregnant or breastfeeding.

Side Effects:

Call your doctor right away if you have any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hand, swelling or tingling in your mouth or throat, chest tightness, trouble breathing, or rash.

Other Side Effects:

You may have the following side effects, but this medicine may also cause other side effects. Tell your doctor if you have side effects that you think are caused by this medicine.

  • Nausea or diarrhea (2)


1. Hobbs C: Using milk thistle. Herbs for Health 1997; July/August.

2. Di Carlo G, Autore G, Izzo AA et al: Inhibition of intestinal motility and secretion by flavonoids in mice and rats: structure-activity relationships. J Pharm Pharmacol 1993; 45:1054-1059.

3. Brinker F: Herb Contraindications and Drug Interactions. Eclectic Institute Inc, Sandy, OR; 1997.

4. Rajnarayana K, Reddy MS, Vidyasagar J et al: Study on the influence of silymarin pretreatment on metabolism and disposition of metronidazole. Arzneim-Forsch./DrugRes 2004; 54(2):109-113.

Last Updated: 7/4/2018
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