Milk thistle (silybum marianum) is a member of the daisy family that’s native to Europe but can now be found globally. Often considered a common weed, milk thistle thrives in a wide range of conditions and locations, including on trailsides, in pastures and along roads.
Limited research suggests supplementing with milk thistle may support liver health, among other potential benefits. Read on to learn what science says about this herb’s potential role in health and wellness, as well as safety and dosage considerations.
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What Is Milk Thistle?
Milk thistle is a common weed also used as a supplement in herbalism and nutrition, deriving its name from the milk-like sap it contains. The seeds of the plant contain various flavonolignans, which are bioactive compounds found in fruits and vegetables. Research regarding the potential health benefits of milk thistle centers around silymarin, a blend of flavonolignans extracted from milk thistle seeds.
Milk thistle has a long history of documented use as a medicinal herb, possibly dating as far back as the first century A.D. Meanwhile, silymarin was first isolated in supplement form during the late 1960s. Today, it can be found in tinctures, extracts, capsules and tablets formulated to improve a wide range of conditions and promote well-being.
Milk Thistle Benefits
The silymarin found in milk thistle may provide a wide range of health benefits related to detoxification and inflammation, according to research. While more well-designed human trials are needed to confirm these benefits, preliminary studies show milk thistle may be beneficial when it comes to certain health conditions.
May Support Liver Health
Researchers suspect that non-alcoholic fatty liver disease affects approximately 25% of the global population, according to a 2019 review in Hepatology[1]Younossi Z, Tacke F, Arrese M, et al. Global Perspectives on Nonalcoholic Fatty Liver Disease and Nonalcoholic Steatohepatitis. Hepatology. 2019;69(6):2672-2682. .
Milk thistle may play a complementary therapeutic role in managing liver disease because of its potent antioxidative properties, says Amylee Amos, Ph.D., a registered nurse based in Seattle. In fact, most research into the herb focuses on milk thistle’s effect on liver disease and its suspected ability to reduce cytokines, or inflammatory cells. Milk thistle may simultaneously inhibit free radicals, highly reactive molecules that create oxidative stress over time, resulting in inflammation.
What’s more, milk thistle may be able to reduce liver fibrosis by protecting the organ against toxins, maintaining healthy antioxidant levels and reducing the presence of tumor enhancing cells. However, further clinical trials are needed to support these claims.
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May Support Healthy Blood Sugar
Milk thistle may support healthy blood sugar and insulin levels for individuals with a risk or diagnosis of type 2 diabetes. While large clinical trials don’t yet exist to support this potential benefit, small human studies yield promising results.
A 2016 meta-analysis in the Journal of Diabetes Research compiled results from five human studies that examined the effects of milk thistle on type 2 diabetes, with each study demonstrating improved glycemic control and minimal complications.
While more research is needed to understand the relationship between milk thistle and blood sugar management, early human studies suggest it may be a potential benefit of the herb.
Cancer Treatment Support
Milk thistle may decrease cancerous tumor growth, according to research. A comprehensive 2022 review in the Iranian Journal of Basic Medical Sciences showed promising chemopreventive (anti-cancer) results with milk thistle use in liver, pancreatic, prostate and breast cancer[2]Emadi SA, Rahbardar MG, Mehri S, Hosseinzadeh H. A review of therapeutic potentials of milk thistle (Silybum marianum L.) and its main constituent, silymarin, on cancer, and their related patents. Iranian Journal of Basic Medical Sciences. 2022;25(10):1166-1176.. .
Further, a 2021 study in Biomedicine and Pharmacotherapy concluded that silymarin, milk thistle’s active compound, reduces inflammation and cancer metastasis, meaning milk thistle may play a role in suppressing cancerous tumors.
Milk thistle’s chemopreventive properties lead researchers to believe that milk thistle, in tandem with chemotherapy, may assist chemotherapy in targeting the diseased areas of the body while simultaneously reducing the toxicity of chemotherapy against normal cells. Some medical providers utilize silymarin administration during chemotherapy for this reason.
May Reduce Inflammation
In addition to the liver, milk thistle may have an anti-inflammatory effect in other tissues and organs throughout the body due to its role in reducing inflammation in the mitochondrias of the cells. Meanwhile, preliminary research suggests milk thistle’s potential anti-inflammatory properties may benefit chronic diseases resulting from or causing extensive inflammation. Further research is needed to further understand the mechanism of this potential health benefit.
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Is Milk Thistle Safe?
Milk thistle is generally well tolerated and doesn’t appear to be toxic to humans in any studied amount, according to research. Even at a high dose of 2,100 milligrams per day for 24 weeks, study participants showed minimal side effects, per a 2019 review in Phytotherapy Research[3]Soleimani V, Delghandi PS, Moallem SA, Karimi G. Safety and toxicity of silymarin, the major constituent of milk thistle extract: An updated review. Phytotherapy Research. 2019;33(6):1627-1638. . Uncommon side effects may include gastrointestinal effects, such as diarrhea or nausea, in some users.
While research suggests milk thistle is generally safe, it may pose risks to some individuals. “People who have a ragweed allergy are at higher risk of being allergic to milk thistle (as the two plants are botanically related), so it’s important to use caution when starting a new supplement,” says Kayley Myers, a registered dietitian and founder of Freedom and Glory Nutrition, a private nutrition practice in Springfield, Missouri. Those susceptible to a ragweed and milk thistle allergy may also find potential allergic reactions with chrysanthemums, marigolds, chamomile, yarrow or daisies. Meanwhile, research suggests ragweed may interact with several antipsychotic medications, birth control pills and hormone replacement therapy.
Symptoms of a ragweed allergy, and potentially a milk thistle allergy, may include congestion, a watery nose, itchy or watery eyes and cough. However, more severe allergies may elicit shortness of breath and feelings of tightness or pain in the chest.
As research into milk thistle safety is limited, consult a registered dietitian nutritionist or a health care provider prior to taking the supplement in any form.
Milk Thistle Dosage and How to Take It
Milk thistle, like many herbal supplements, is available in a variety of forms, including capsules, tablets and liquid extracts. Dosages differ depending on the brand and product and daily dosages may vary between 400 to 620 milligrams per day, though a standard milk thistle dosage doesn’t exist currently[4]Tighe SP, Akhtar D, Iqbal U, Ahmed A. Chronic Liver Disease and Silymarin: A Biochemical and Clinical Review. Journal of Clinical and Translational Hepatology. 2020;8(4):454-458. . Experts suggest looking for a supplement consisting of a minimum of 70% to 80% silymarin from the seeds of the plant.
Who to Speak With About Milk Thistle
Although milk thistle is generally well-tolerated and regarded as safe, individual recommendations about taking this supplement may vary based on a person’s health history, current medication and supplement list, as well as other unique factors.
Before beginning any new herbal supplement, one should consult a primary care provider, an allergist (especially if someone is at risk of a milk thistle allergy) and/or a registered dietitian nutritionist to determine if milk thistle is right for their needs and how to safely add the supplement to their daily regimen.
