Milk Thistle
OTHER NAME(S): holy thistle, Mary thistle, milk thistle, Silybum marianum
Overview
Milk thistle is a plant called Silybum marianum. Milk thistle fruit and seeds are used to make tea or dietary supplements, such as tablets or capsules. People often take milk thistle for liver problems and diabetes, although its benefits are not well defined. Common side effects may include diarrhea, upset stomach, and nausea. Before taking milk thistle, make sure to tell your health care provider about any health conditions you have or medicines you are taking.
Uses
What is milk thistle used for?
Milk thistle (S. marianum) is commonly used to help treat or prevent certain liver problems. It is also sometimes used for diabetes. However, the benefits of milk thistle are not well-defined.
The FDA has not reviewed milk thistle for safety and effectiveness, and it is not approved by the FDA. Learn more about dietary supplements here.
How does milk thistle work (mechanism of action)?
Milk thistle is a plant called S. marianum. It is also sometimes called holy thistle or Mary thistle. Milk thistle dietary supplements are usually made using the seeds and fruit of the plant.
Milk thistle contains a substance called silymarin, which is made up of many different chemicals, including silybin. Silymarin and silybin are thought to work as antioxidants and to help protect the liver from certain toxins, but it is not clear if milk thistle can help improve or prevent liver problems. It is also unclear whether milk thistle can help lower blood sugar in people with diabetes.
Herbal products like milk thistle naturally contain many different chemicals, such as silymarin and silybin. The amount of each chemical in a specific milk thistle product may vary. Different amounts of silymarin or silybin may change the effects of milk thistle on the body. Some milk thistle dietary supplements are made to contain a specific amount of these substances. Also, some dietary supplements made from milk thistle only contain either silymarin or silybin.
How should I store milk thistle?
You should store milk thistle according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.
Side Effects
What are the most common side effects of milk thistle?
The most common side effects of milk thistle are listed below. These side effects may vary depending on the dose you are taking or the specific product you are using. Tell your health care provider if you have any of these side effects that bother you.
- Bloating
- Diarrhea
- Nausea
- Upset stomach
There may be other side effects of milk thistle that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.
What are the serious side effects of milk thistle?
While less common, the most serious side effects of milk thistle are described below, along with what to do if they happen.
Severe Allergic Reactions. Milk thistle may cause allergic reactions, which can be serious. Stop taking milk thistle and get help right away if you have any of the following symptoms of a serious allergic reaction.
- Breathing problems or wheezing
- Racing heart
- Fever or general ill feeling
- Swollen lymph nodes
- Swelling of the face, lips, mouth, tongue, or throat
- Trouble swallowing or throat tightness
- Itching or skin rash
- Bumps on the skin called hives, which can be red, pink, white, or brown depending on your skin tone
- Nausea or vomiting
- Dizziness, feeling lightheaded, or fainting
- Stomach cramps
- Joint pain
Precautions
Who should not use milk thistle?
Allergies to Ingredients. People who are allergic to any of the following should not take milk thistle.
- Milk thistle
- Silybin
- Silybum marianum
- Silymarin
- Any of the ingredients in the specific product
Your pharmacist can tell you all of the ingredients in the specific milk thistle products they stock.
What should I know about milk thistle before using it?
Milk thistle is a dietary supplement. It cannot be marketed to treat or cure a disease.
Read and follow the directions on the specific product you are taking, or take it as recommended by your health care provider.
Keep milk thistle out of the reach of children.
Herbal products, such as milk thistle, naturally contain many different chemicals. The amount of each chemical in a specific milk thistle product can change for many reasons, including the area where the plant was grown, the weather during growth, the time of year when it was harvested, and the way the plant was processed after it was harvested. If you switch to a new bottle or a different brand, you may not have the same effects or side effects because of this variability. Talk to your health care provider if you have questions or concerns.
Milk thistle is available in many different forms, including as a tea and as dried ground powder found in capsules or tablets. Each of these forms may contain different amounts of the chemicals that are naturally found in the plant.
The FDA has not tested milk thistle products to confirm that they contain the ingredients stated on their labels. Some dietary supplements have been tested by third-party organizations to confirm that they contain the ingredients listed on their labels and do not contain any harmful chemicals. Learn more about how to choose a safe dietary supplement product here.
What should I tell my health care provider before using milk thistle?
Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if milk thistle is right for you.
In particular, make sure that you discuss any of the following.
Current and Past Health Conditions.Before taking milk thistle, tell your health care provider if you have any of the following.
- Cancer
- Liver problems
- Are receiving chemotherapy or radiation, which is a treatment for cancer
Allergies to Certain Plants.Milk thistle is part of the Asteraceae (daisy) family of plants. People who have an allergy to other plants in this family may be more likely to have an allergic reaction to milk thistle. Some examples of other common plants in the Asteraceae family include arnica, marigold, chamomile, yarrow, ragweed, asters, and chrysanthemums. If you have an allergy to one of these plants, talk to your health care provider before taking milk thistle.
Other Medicines and Supplements.Milk thistle may interact with other medicines and supplements. Before taking milk thistle, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.
Pregnancy. It is not known if or how milk thistle could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.
Breastfeeding. It is not known if milk thistle passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.
Interactions
Does milk thistle interact with foods or drinks?
There are no known interactions between milk thistle and foods or drinks.
It is unknown if drinking alcohol will affect milk thistle.
Does milk thistle interact with medicines (drug interactions)?
Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.
In particular, make sure that you discuss if you are receiving chemotherapy, which is medicine used to treat cancer.
The interactions between milk thistle and medicines are not fully understood. As with most dietary supplements, research on drug interactions with milk thistle is incomplete. Always check with your health care provider before using milk thistle with any medicines.
Dosing
What should I do if I accidentally use too much milk thistle?
If you or someone else has used too much milk thistle, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.
The dose of milk thistle is usually based on the amount of silymarin contained in the product. Silymarin is the substance in milk thistle that is thought to have effects in the body. Read the product label closely and speak to a health care provider about how to use milk thistle safely. Do not take double or extra doses, even if you miss a dose.
References
- Drugs and Lactation Database (LactMed) [Internet]: “Milk thistle.”
- Memorial Sloan Kettering Cancer Center: “Milk thistle.”
- National Cancer Institute: “Milk Thistle (PDQ) - Health Professional Version,” “Milk Thistle (PDQ) - Patient Version.”
- National Center for Complementary and Integrative Health: “Hepatitis C and Dietary Supplements,” “Milk Thistle,” “Hepatitis C and Dietary Supplements: What the Science Says.”