April 2020 Issue

Supplements: Milk Thistle
By Brianna Tobritzhofer, MS, RD, LD
Today’s Dietitian
Vol. 22, No. 4, P. 14

Though it’s likely safe, research is mixed on the supplement’s efficacy for liver health and other uses.

Milk thistle is an herbal remedy that’s been used for thousands of years to treat a variety of ailments, especially liver conditions. In fact, milk thistle is the most commonly used herbal supplement in the United States for liver problems.1

Consumer interest in this top-selling botanical has peaked in recent years. Proponents of milk thistle claim it has health benefits beyond liver health, from preventing brain damage to boosting breastmilk production.

Is there truth behind these claims? This article discusses what RDs need to know about milk thistle, from its potential health benefits to instructions for use and possible adverse effects.

What Is Milk Thistle?
Milk thistle is derived from the milk thistle plant, Silybum marianum. The active ingredients in milk thistle are a group of plant compounds called silymarin, which have several antioxidative, antiviral, and anti-inflammatory properties.2

Although milk thistle is native to the Mediterranean region, its use for health ailments is known all over the world. It grows in parts of Europe, Russia, Asia, Africa, and Australia, as well as North and South America.1

Other common names for milk thistle include Mary thistle, holy thistle, and silymarin (after its best-known plant compounds). The purple flowers of the thorny milk thistle plant contain a milky white liquid that’s extracted and used in supplements. Milk thistle supplements typically are consumed orally.1

A Growing Trend
Despite milk thistle being around for centuries, its popularity as a supplement has increased in recent years. This often is attributed to the trend of liver “detox” and greater consumer perception of milk thistle’s potential health benefits.

Sales of milk thistle supplements were estimated to grow by 6% in 2019, according to a report published in April 2019 by Research Report Insights. Approximately 890 tons of milk thistle supplements were sold in 2018, with North America and Europe purchasing the majority. Softgels are the most popular variety of milk thistle supplements, but they’re also available as liquid extract and tablets.3

Possible Health Benefits
Milk thistle has been most publicized for its purported liver-protective effects. Research has shown that milk thistle may help reduce inflammation and liver damage caused by free radicals. It has the ability to down-regulate and inhibit inflammatory cytokines and increase the production of molecules that reduce inflammation, such as interleukin 10 and glutathione.2

Several studies have focused on the role that milk thistle may play in treating nonalcoholic fatty liver disease (NAFLD). In one trial, individuals with NAFLD who supplemented with 600 mg of milk thistle daily for 12 months were found to have lower levels of fasting insulin, liver enzymes, and other plasma markers of liver fibrosis.2

Some studies have noted mild improvement in symptoms, treatment, and survival among individuals with hepatitis C, Cooley’s anemia, liver cancer, and cirrhosis due to alcoholic liver disease.1

Although the research conducted on milk thistle and liver conditions is somewhat promising, more studies are needed before a conclusion can be made about its role in liver health. There’s no conclusive evidence that milk thistle can prevent, cure, or treat liver conditions. More clinical trials also are necessary to determine the dose and length of treatment needed to treat liver conditions with milk thistle.

There’s some evidence that milk thistle may have benefits for other body systems and conditions. For example, compounds in milk thistle may improve blood sugar control and insulin sensitivity among individuals with type 2 diabetes. A recent review and meta-analysis of five randomized controlled trials discovered that routine use of milk thistle supplements was associated with a significant reduction in fasting blood glucose and HbA1c levels among 270 patients with diabetes.4 However, the quality of the studies reviewed was low, and further research is warranted.

A few other small human studies have found that milk thistle supplements may help improve acne and increase breastmilk production in breast-feeding mothers.5,6 There also are many anecdotal reports for milk thistle’s use in treating indigestion, but the research behind these claims is lacking.

The remaining research available on milk thistle supplements is focused on findings from animal and in vitro studies. Some of these suggest that the antioxidative, anti-inflammatory, and antiviral properties of milk thistle may have anticancer effects and help prevent side effects from cancer treatment modalities.7,8 In addition, experimental studies show that milk thistle may be useful for protecting against osteoporosis and age-related decline in brain function.9-11

Unfortunately, the best dosage and length of treatment using milk thistle is unknown due to the limited research behind it. Patients should speak with their health care providers for individualized recommendations for milk thistle use based on their health conditions, medications, lifestyle, and treatments.

Supplements on the market contain varying dosages of milk thistle. The dosing instructions for the supplements vary based on concentration and intended use, which should always be indicated on the supplement label. Some research suggests that a dosage of 140 to 420 mg milk thistle extract daily holds potential benefits for blood sugar control, but the proper dosage for other conditions or benefits, including liver health, is unclear.12

Silymarin concentration typically is listed on milk thistle supplement labels as well, which varies by the brand. There’s not currently enough research to determine what concentration works best for individuals who take milk thistle supplements.

Adverse Effects
Milk thistle supplements are well tolerated by most people when taken by mouth. There are minimal reported side effects, which generally are limited to gastrointestinal complaints.2

It’s important to note that people allergic to plants in the same family as milk thistle, such as ragweed, chrysanthemum, marigold, and daisy, are at risk of having an allergic reaction when using supplements. In addition, people with diabetes and hormone-sensitive conditions should be cautious with milk thistle, as it may have estrogenic effects and has the potential to lower blood sugar levels.1

Pregnant women are advised to avoid using milk thistle supplements, as their safety hasn’t been confirmed in this population. The same holds true for individuals with compromised immune systems.1

Although milk thistle supplements generally are considered to be safe, clients should always consult with their health care providers before trying them. In addition, IV treatments with milk thistle and any modalities of supplementation other than oral should be avoided, as their safety is unknown.

Recommendations for Clients
Despite the limited evidence regarding the health benefits of milk thistle, it’s inevitable that claims behind it will continue to attract consumers. Thus, RDs should be prepared with appropriate recommendations to counsel their patients on how to safely use it.

As an overall safe supplement, RDs can make informed recommendations to patients who take milk thistle supplements based on the evidence above. Although there’s no conclusive scientific evidence behind milk thistle’s purported health benefits, it shows potential in its ability to support liver function and aid in improving other health ailments.

If patients choose to use milk thistle supplements, it’s important that they pair them with an overall nutritious diet, healthful lifestyle, and adequate medical care. Milk thistle supplements shouldn’t be used as a substitute for any of the latter.

RDs also should be prepared with recommendations for milk thistle supplement brands that are high quality and pharmaceutical grade, meaning they’ve been evaluated by a third party such as ConsumerLab.com or US Pharmacopeia to verify the accuracy of their claimed contents.

— Brianna Tobritzhofer, MS, RD, LD, is the senior manager of nutrition services for Open Arms of Minnesota. She also provides freelance writing services through her business, Bri Toby Nutrition Company.


1. Milk thistle. National Center for Complementary and Integrative Health website. https://nccih.nih.gov/health/milkthistle/ataglance.htm. Updated September 2016. Accessed January 4, 2020.

2. Achufusi TGO, Patel RK. Milk Thistle. Treasure Island, FL: StatPearls Publishing; 2019:1-8.
3. Global market study on milk thistle supplements, 2019-2027: consumer awareness on preventive healthcare fuels demand. Research Report Insights website. https://www.researchreportinsights.com/report/91/milk-thistle-supplements-market. Published April 2019. Accessed January 3, 2020.

4. Voroneanu L, Nistor I, Dumea R, Apetrii M, Covic A. Silymarin in type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials. J Diabetes Res. 2016;2016:5147468.

5. Shie Morteza M, Hayati Z, Namazi N, Abdollahimajd F. Efficacy and safety of oral silymarin in comparison with oral doxycycline and their combination therapy in the treatment of acne vulgaris. Dermatol Ther. 2019;32(6):e13095.

6. Di Pierro F, Callegari A, Carotenuto D, Tapia MM. Clinical efficacy, safety, and tolerability of BIO-C (micronized silymarin) as a galactagogue. Acta Biomed. 2008;79(3):205-210.

7. Polachi N, Bai G, Li T, et al. Modulatory effects of silibinin in various cell signaling pathways against liver disorders and cancer — a comprehensive review. Eur J Med Chem. 2016;123:577-595.

8. Siegel AB, Stebbing J. Milk thistle: early seeds of potential. Lancet Oncology. 2013;14(10):929-930.

9. Mohd Fozi NF, Mazlan M, Shid AN, Isa Naina M. Milk thistle: a future potential anti-osteoporotic and fracture healing agent. Curr Drug Targets. 2013;14(14):1659-1666.

10. Abdul Jalil MA, Shuid AN, Muhammad N. Osteoporotic fracture healing: potential use of medicinal plants from the tropics. Curr Drug Targets. 2013;14(14):1651-1658.

11. Galhardi F, Mesquita K, Monserrat JM, Barros DM. Effect of silymarin on biochemical parameters of oxidative stress in aged and young rat brain. Food Chem Toxicol. 2009;47(1):2655-2660.

12. Milk thistle. Drugs.com website. https://www.drugs.com/npp/milk-thistle.html. Updated March 1, 2019. Accessed January 3, 2020.