Milk thistle—Does it do a body good?

Dear Alice,

What part 'milk thistle' is used for medication and how?

Dear Reader,

Milk thistle, also known as St. Mary’s thistle, holy thistle, and wild artichoke, is a plant that’s been used as a medicinal treatment for more than 2,000 years. Don’t be fooled by the name, though; milk thistle doesn’t contain or produce any milk. In fact, it’s part of the Asteraceae plant family, which also includes sunflowers, daisies, chrysanthemums, and chamomile. Crushing the leaves of the plant releases a milky white sap, hence the name! Historically, milk thistle was a common herbal remedy for a variety of digestive and liver problems, but these days, people are more likely to take milk thistle using oral capsules, tablets, or liquid extract rather than foraging the plant themselves. While there is some evidence of its positive benefits on liver functioning, scientific research is still limited. Some folks would be wise to avoid milk thistle due to the risk of side effects or adverse interactions, including pregnant or breastfeeding people, people with hormone-related cancers, people who are allergic to any plant in the Asteraceae family, and people who take certain medications such as hormonal birth control, diabetes medications, antipsychotics, and some other medications that are metabolized in the liver.

The active ingredient in milk thistle is silymarin, an antioxidant compound which may help reduce inflammation, repair damaged liver cells, and protect against future liver damage. Milk thistle products are most commonly available in various forms such as oral capsules, tablets, and liquid extract, which often contain about 70 to 80 percent silymarin, typically extracted from the seeds of milk thistle.

While there are many animal studies demonstrating the positive effects of milk thistle on liver functioning, mushroom poisoning, and cancer outcomes, human studies remain limited with mixed results. Some studies in humans support the use of milk thistle for treatment of viral hepatitis, alcoholic hepatitis, and alcoholic cirrhosis (all conditions impacting the liver), but overall results are mixed. In Europe, milk thistle is approved for use in humans as an emergency antidote for ingesting death cap mushroom. However, in the US, the Food and Drug Administration (FDA) hasn't yet approved it for human use in mushroom poisoning (though animal studies are promising). Additionally, milk thistle may be beneficial in cancer treatment: some small human studies found that its use reduced some negative symptoms of cancer treatments, such as side effects of chemotherapy and radiation-related rashes. However, large-scale clinical trials with humans are limited, which means this evidence is inconclusive for now. For all of these conditions, more clinical trials are needed before the FDA might consider approving its use in humans.

Though milk thistle likely has few risks and some potential health benefits for some people, it may also have adverse reactions for others. Some human studies have found that milk thistle may occasionally result in diarrhea, nausea, or an upset stomach in some users. It may also cause potentially life-threatening allergic reactions, which are more common in people with allergies to other plants in the Asteraceae family, such as marigolds, ragweed, chamomile, and daisies. Additionally, as there haven’t been enough studies in children and people who are pregnant or breastfeeding to inform safe use of milk thistle, it’s recommended that these groups consult a health care provider before use. Finally, milk thistle may negatively interact with or affect the metabolization of some types of medication, including hormonal birth control, antipsychotics, and other drugs that are metabolized in the liver. Because this list includes many common medications, a discussion with a health care provider is recommended to determine whether or not milk thistle is a safe option.

In fact, consulting a health care provider before trying any type of medicinal treatment (even natural ones) is wise because combining different supplements and medications may have unanticipated and undesirable interactions. These conversations are especially useful before starting herbal supplements such as milk thistle because supplements aren't regulated by the FDA, nor have they been approved in the United States as part of any specific treatment. Kudos to you for looking into the usefulness and safety of herbal supplements—a better understanding is the best way to make informed decisions!

Last updated Dec 02, 2022
Originally published May 02, 2014

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