What Is Milk Thistle?

Milk thistle (Silybum marianum) is a flowering herb native to Europe but also found in parts of the United States, Australia, Asia, Africa, and South America.

Although research is still emerging, milk thistle may be beneficial for conditions relating to the liver and gallbladder. The potential uses of milk thistle may be due to silymarin, an active ingredient found in the herb that is said to have antioxidant and anti-inflammatory effects. 

This article will explore the potential uses of milk thistle. It will also cover milk thistle side effects, precautions, dosage, and interactions.

Dietary supplements are not regulated like drugs in the United States, meaning the Food and Drug Administration (FDA) does not approve them for safety and effectiveness before products are marketed. When possible, choose a supplement that has been tested by a trusted third party, such as USP, ConsumerLabs, or NSF. 

However, even if supplements are third-party tested, that doesn’t mean they are necessarily safe for all or effective in general. Therefore, it is important to talk to your healthcare provider about any supplements you plan to take and to check in about any potential interactions with other supplements or medications.

Supplement Facts

  • Active ingredient(s): Silymarin, Silybin
  • Alternate name(s): Silybum marianum, Carduus marianus
  • Legal status: Legal in the U.S. and sold over-the-counter
  • Suggested dose: No standard dose exists for milk thistle.
  • Safety considerations: Side effects are rare but possible when using milk thistle. Possible side effects include gastroenteritis, diarrhea, headache, and skin reactions.

Purported Uses of Milk Thistle

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian, pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent disease. 

Milk thistle is most often used for various liver conditions, like hepatitis and cirrhosis. But the herb is also believed to be beneficial for other health issues. However, few of these claims are supported by solid evidence.

Below is a look at some of the current research surrounding the uses of milk thistle.

Cirrhosis

Silymarin, an active component of milk thistle, may improve liver function and reduce symptoms of cirrhosis, or scarring of the liver. However, the evidence is conflicting.

One study questioned the benefits of milk thistle for liver diseases. Eighteen clinical trials of 1,088 participants were assessed. Overall, milk thistle compared with placebo or no treatment had no significant effect on mortality, liver disease complications, or liver histology. Further, while liver-related mortality was significantly reduced by milk thistle, this was not seen in any of the high-quality trials.

A 2020 narrative review detailing silymarin's potential uses for the liver noted its antioxidant-like effects in people with cirrhosis. The review went on to say that silymarin may be linked to lower rates of mortality in patients with cirrhosis and liver disease.

Other studies looking at milk thistle for cirrhosis have found conflicting results. Therefore, we cannot definitely say that milk thistle or silymarin should be used to treat cirrhosis.

Hepatitis C

People sometimes use milk thistle for hepatitis C, a viral infection of the liver.

A survey conducted in the United States reported that 23 percent of those polled used herbal supplements for their hepatitis C, with milk thistle being the most common choice. The survey revealed anecdotal evidence of the improved quality of life among those who took milk thistle, despite having no measurable improvements in hepatitis symptoms like liver inflammation.

A study from 2012 confirmed that milk thistle might not have true beneficial effects on hepatitis C. In the study, patients who took silymarin, an active component of milk thistle, daily for 24 weeks had no significant improvements in liver enzymes or other measures compared to those who took the placebo.

Although milk thistle may be helpful in hepatitis C, more research is needed to support these claims.

Type 2 Diabetes

Several studies have suggested that milk thistle may be beneficial for people with type 2 diabetes.

In one such study, a 45-day course of silymarin, the active component of milk thistle, increased antioxidant capacity and reduced generalized inflammation in adults with type 2 diabetes compared with a placebo. According to researchers, these findings suggest that silymarin may improve diabetes symptoms like oxidative stress and inflammation.

A systematic review conducted in 2016 further concluded that using silymarin regularly may reduce fasting blood glucose and HbA1C levels, two important factors in diabetes management. However, the review's authors warned that the quality of the studies was poor and that more research is needed before milk thistle should be recommended for use.

What Are the Side Effects of Milk Thistle?

Side effects are always possible when taking supplements. Milk thistle is generally thought to be safe, but you still may experience side effects when taking it. These side effects may be mild or severe.

Common Side Effects

Although rare, milk thistle may trigger a number of common and mild side effects.

Common side effects of milk thistle reported in studies include:

Typically, side effects will subside once you stop using milk thistle. Consult with your healthcare provider if you experience these and other side effects to find out the best way to proceed.

Severe Side Effects

On extremely rare occasions, milk thistle has caused severe allergic reactions as well as anaphylaxis, a potentially life-threatening allergic reaction.

These reactions may occur if you have an allergy to milk thistle. If left untreated, anaphylaxis can lead to shock, coma, cardiac or respiratory failure, or even death.

Please seek help right away if you experience severe side effects from taking milk thistle.

Precautions

Milk thistle may not be safe for everyone. Certain people should take precautions when using milk thistle, and others may need to avoid it altogether.

Some people may be allergic to milk thistle. Milk thistle may cause an allergic reaction in those with allergies to plants in the same family, like ragweed, chrysanthemum, marigold, and daisy.

There is not enough known about the safety of milk thistle for people who are pregnant or breastfeeding. We also do not know whether milk thistle is safe for children. Therefore, it may be best to avoid milk thistle during these life stages.

It is also recommended that people with diabetes use caution when taking milk thistle, as it may reduce blood sugar.

Finally, those with hormone-sensitive conditions, including certain cancers, may need to avoid using milk thistle. In some studies, silibinin, an active component of milk thistle, has been shown to have estrogen-like effects.

Dosage: How Much Milk Thistle Should I Take?

Always speak with a healthcare provider before taking a supplement to ensure that the supplement and dosage are appropriate for your individual needs. 

Currently, there are no guidelines regarding a standard dose of milk thistle.

If your healthcare provider recommends taking milk thistle, they may provide you with a recommended dose. Dosage is also typically listed on the nutrition label of supplements.

You should follow dosage directions to prevent side effects. Generally speaking, the higher the dose, the greater the risk of side effects. Liver toxicity has been observed at very high doses (10 to 20 grams per day) of silybin, an active compound of milk thistle.

Current studies on milk thistle use a wide range of doses. Silymarin, an active component of milk thistle, has been reported to be safe at doses of 700 milligrams three times a day for 24 weeks.

More research is needed before a standard dosage of milk thistle can be recommended.

What Happens If I Take Too Much Milk Thistle?

It is possible to take too much milk thistle.

Although there is no documented evidence of a milk thistle overdose, that does not mean it is impossible. Use milk thistle as directed to prevent an overdose.

Toxicity is also possible if too much milk thistle is taken. Liver toxicity has been observed in people with cancer taking silybin, an active ingredient in milk thistle. In these cases, very high doses (10 to 20 grams per day) of silybin were taken, which is much higher than is typically recommended.

Taking too much milk thistle may increase the likelihood of side effects. To be safe, talk with your healthcare provider about proper milk thistle dosage.

Interactions

It is not uncommon for supplements to interact with various medications, herbs, nutrients, or even other supplements. Milk thistle may interact with certain medications.

Substances in milk thistle may reduce blood sugar. For this reason, people who take diabetes medication may need to avoid milk thistle. Consult your healthcare provider if this applies to you.

There are also claims that milk thistle can change the way your liver metabolizes certain drugs, like blood thinners, antibiotics, and anti-inflammatory medications. However, there is no solid evidence that supports these claims.

Regardless, interactions are still possible. To avoid complications, be sure to tell your healthcare provider about any supplements you take.

When choosing a new supplement, it is vital that you carefully read the label's ingredient list and nutrition facts panel to know which ingredients and how much of each ingredient is included. Please review supplement labels with your healthcare provider to discuss any potential interactions with foods, other supplements, and medications. 

Milk thistle capsules
Verywell / Anastasia Tretiak

How to Store Milk Thistle

An important part of taking supplements is proper storage.

Store milk thistle supplements in a cool, dry place. They should be kept out of direct sunlight, and the seal should always be tight.

Keep supplements in areas out of reach of pets and children.

Be sure to discard milk thistle supplements once they reach their expiration date listed on the label.

Similar Supplements

There are other supplements that work similarly to milk thistle. The following list is not exhaustive.

Similar supplements to milk thistle include:

  • Curcumin: Both animal and human trials have shown that curcumin, an active ingredient of turmeric, may help with cirrhosis. A recent pilot study found that people with cirrhosis who took 1,000 milligrams of curcumin a day for three months had decreased disease severity and lower cirrhosis activity scores compared to those who took a placebo.
  • Vitamin E: Vitamin E is an important nutrient that works as an antioxidant. These antioxidant effects may be beneficial for those with chronic hepatitis C. In one small human study, vitamin E supplementation led to decreased enzymes associated with liver damage and hepatitis.
  • Resveratrol: Resveratrol is an antioxidant naturally occurring in grape vines, berries, and peanuts. Evidence suggests that resveratrol may reduce oxidative stress and decrease both insulin resistance and inflammation in people with diabetes. This does not necessarily mean that consuming resveratrol will be useful for you if you have diabetes, as more studies are needed. Supplements should never replace standard medical care.

Please talk with your healthcare provider about the best supplement for you. It's typically recommended to avoid taking multiple supplements for the same cause at the same time.

Frequently Asked Questions

  • What is silymarin?

    Silymarin is an active compound found in milk thistle seeds. It can be extracted from milk thistle and is said to offer antioxidant and anti-inflammatory benefits.

  • Does milk thistle cause any side effects?

    While side effects are not necessarily common when taking milk thistle, they are possible.

    Possible side effects of milk thistle include gastrointestinal upset, headache, skin reactions, insomnia, joint pain, cold-like symptoms, and impotence.

    Milk thistle can also cause an allergic reaction in some people. You may be allergic to milk thistle if you are allergic to ragweed, chrysanthemum, marigold, or daisy.

  • Is milk thistle available as a tea?

    Milk thistle comes in many forms, including tea. You can find milk thistle as loose-leaf tea or in pre-portioned tea bags.

    Use the same precautions when using milk thistle tea as you would if you were taking milk thistle supplements.

Sources of Milk Thistle & What to Look For

Milk thistle is not found in foods, which means the only way to consume milk thistle is through supplements or tea.

Besides supplements, milk thistle is available as a tea. You can find milk thistle tea bags or loose-leaf milk thistle tea to steep with hot water. However, it is unknown if milk thistle tea provides the same suggested benefits as milk thistle supplements.

Milk Thistle Supplements

Milk thistle supplements are commonly sold in capsule form but are also available as tablets, soft gels, tea, and liquid extracts.

Some, but not all, milk thistle supplements are vegan. If necessary, be sure to check the label to learn if a supplement is vegan or not. Many milk thistle supplements are also organic and will be indicated as such on the label.

Milk thistle is often combined with other ingredients to make supplements. These combination supplements may list health claims on the label. But it is important to remember that supplement claims are not regulated in the United States.

Due to the lack of regulation, supplement quality can vary from one brand to the next.

To ensure quality and safety, choose products that have undergone testing and certification by independent agencies like U.S. Pharmacopeia (USP), ConsumerLab, and NSF International.

Summary

Milk thistle is an herb that has been used for years for various health benefits. However, many of these potential benefits are not backed by science.

Milk thistle is thought to be safe for most people, but precautions should be taken as side effects are possible. It can be consumed in supplement form or as a tea.

Talk with your healthcare provider before starting milk thistle to make sure it is the right supplement for you.

18 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Center for Complementary and Integrative Health. Milk thistle.

  2. Achufusi TGO, Patel RK. Milk thistle. In: StatPearls. StatPearls Publishing; 2022.

  3. Rambaldi A, Jacobs BP, Gluud C. Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases. Cochrane Database Syst Rev. 2007;2007(4):CD003620. doi:10.1002/14651858.CD003620.pub3

  4. Gillessen A, Schmidt HH. Silymarin as supportive treatment in liver diseases: a narrative reviewAdv Ther. 2020;37(4):1279-1301. doi:10.1007/s12325-020-01251-y.

  5. Seeff LB, Curto TM, Szabo G, et al. Herbal product use by persons enrolled in the hepatitis C Antiviral Long-Term Treatment Against Cirrhosis (HALT-C) Trial. Hepatology. 2008;47(2):605-12. doi:10.1002/hep.22044

  6. Fried MW, Navarro VJ, Afdhal N, et al. Effect of silymarin (milk thistle) on liver disease in patients with chronic hepatitis C unsuccessfully treated with interferon therapy: a randomized controlled trialJAMA. 2012;308(3):274-282. doi:10.1001/jama.2012.8265.

  7. Ebrahimpour koujan S, Gargari BP, Mobasseri M, Valizadeh H, Asghari-jafarabadi M. Effects of Silybum marianum (L.) Gaertn. (silymarin) extract supplementation on antioxidant status and hs-CRP in patients with type 2 diabetes mellitus: a randomized, triple-blind, placebo-controlled clinical trial. Phytomedicine. 2015;22(2):290-296. doi:10.1016/j.phymed.2014.12.010

  8. 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 trialsJ Diabetes Res. 2016;2016:5147468. doi:10.1155/2016/5147468.

  9. Yang Z, Zhuang L, Lu Y, Xu Q, Chen X. Effects and tolerance of silymarin (milk thistle) in chronic hepatitis C virus infection patients: a meta-analysis of randomized controlled trials. Biomed Res Int. 2014;2014:941085. doi:10.1155/2014/941085

  10. Milk thistle. In: Drugs and Lactation Database (LactMed). Bethesda (MD): National Library of Medicine (US); February 20, 2022.

  11. Dupuis ML, Conti F, Maselli A, et al. The Natural agonist of estrogen receptor β silibinin plays an immunosuppressive role representing a potential therapeutic tool in rheumatoid arthritisFront Immunol. 2018;9:1903. doi:10.3389/fimmu.2018.01903.

  12. Loguercio C, Festi D. Silybin and the liver: from basic research to clinical practiceWorld J Gastroenterol. 2011;17(18):2288-2301. doi:10.3748/wjg.v17.i18.2288.

  13. Soleimani V, Delghandi PS, Moallem SA, Karimi G. Safety and toxicity of silymarin, the major constituent of milk thistle extract: An updated reviewPhytother Res. 2019;33(6):1627-1638. doi:10.1002/ptr.6361.

  14. Kazazis CE, Evangelopoulos AA, Kollas A, Vallianou NG. The therapeutic potential of milk thistle in diabetes. Rev Diabet Stud. 2014;11(2):167-74. doi:10.1900/RDS.2014.11.167

  15. Nouri-Vaskeh M, Malek Mahdavi A, Afshan H, Alizadeh L, Zarei M. Effect of curcumin supplementation on disease severity in patients with liver cirrhosis: a randomized controlled trialPhytother Res. 2020;34(6):1446-1454. doi:10.1002/ptr.6620.

  16. Bunchorntavakul C, Wootthananont T, Atsawarungruangkit A. Effects of vitamin E on chronic hepatitis C genotype 3: a randomized, double-blind, placebo-controlled studyJ Med Assoc Thai. 2014;97 Suppl 11:S31-S40.

  17. Nanjan MJ, Betz J. Resveratrol for the management of diabetes and its downstream pathologiesEur Endocrinol. 2014;10(1):31-35. doi:10.17925/EE.2014.10.01.31.

  18. Mulrow C, Lawrence V, Jacobs B, et al. Milk thistle: effects on liver disease and cirrhosis and clinical adverse effects: summary. Agency for Healthcare Research and Quality (US); 2000.

Additional Reading

By Brittany Lubeck, RD
Brittany Lubeck, RD, is a nutrition writer and registered dietitian with a master's degree in clinical nutrition. 

Originally written by
Cathy Wong
Cathy Wong

Cathy Wong is a nutritionist and wellness expert. Her work is regularly featured in media such as First For Women, Woman's World, and Natural Health.

Learn about our editorial process