Milk thistle (Silybum marianum) is said to have certain health benefits, including liver health, diabetes management, cancer treatment, and more. However, research is not conclusive on its uses.

Milk thistle is a flowering herb native to Europe but is also found in parts of the United States, Australia, Asia, Africa, and South America.¹ The benefits 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.²

Camini FC, Costa DC. Silymarin: not just another antioxidant. J Basic Clin Physiol Pharmacol. 2020;31(4):/j/jbcpp.2020.31.issue-4/jbcpp-2019-0206/jbcpp-2019-0206.xml. doi:10.1515/jbcpp-2019-0206

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

What Is Milk Thistle Used For?

Milk thistle is most often used for various liver conditions, like hepatitis and fatty liver disease.²

Camini FC, Costa DC. Silymarin: not just another antioxidant. J Basic Clin Physiol Pharmacol. 2020;31(4):/j/jbcpp.2020.31.issue-4/jbcpp-2019-0206/jbcpp-2019-0206.xml. doi:10.1515/jbcpp-2019-0206 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 research surrounding the uses of milk thistle. Keep in mind that 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.

Interactions With Milk Thistle

Milk thistle may interact with certain medications and supplements. Substances in milk thistle may reduce blood sugar, a concern for people living with diabetes.³ Milk thistle may 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.

Liver Health and 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 (death), liver disease complications, or liver histology (microscopic anatomy of the liver). Further, while liver-related mortality was significantly reduced by milk thistle, this was not seen in any of the high-quality trials.⁴

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.⁵

Other studies looking at milk thistle for cirrhosis have found conflicting results. Therefore, it is not known whether milk thistle or silymarin should be used to treat cirrhosis.

What Is Silymarin?

Silymarin is an active component of milk thistle, which is not found in foods. Milk thistle supplements containing silymarin are commonly sold as teas or in capsule form, but are also available as tablets, soft gels, and liquid extracts. Some, but not all, milk thistle supplements are vegan.

Hepatitis C

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

A survey conducted in the U.S. reported that 23% 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.⁶

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.⁷

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.⁸

A systematic review (summary of medical literature on a specific topic) 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

Breast Milk Production

Milk thistle often is used as a galactalogue, a food or supplement that people who are chest feeding take to improve milk production. Trigonella foenum-graecum (fenugreek) also is used for this reason.

The benefits of milk thistle remain unclear for this purpose and the limited research on milk thistle and breast milk has been done primarily in animals. One small clinical trial showed an increase in breast milk formation in humans using milk thistle, but researchers caution that more studies are needed

Cancer

The research on milk thistle’s use in cancer patients is promising, although more research is needed to determine its benefits. Studies on cancer cell lines (done in the laboratory) have found that elements in milk thistle:¹¹

National Cancer Institute PDQ Integrative, Alternative, and Complementary Therapies Editorial Board. Milk thistle (PDQ®): Health Professional Version.

Boost the impact of chemotherapy drugs like cisplatin and doxorubicin when treating ovarian and breast cancer
Have direct benefits against prostate, breast, and certain cervical cancer cells
Do not stimulate the growth of leukemia cells
Can be used to complement treatment for liver cancer¹²

Researchers also are looking at how milk thistle might complement traditional care and treatment in people diagnosed with gastrointestinal cancers.

Skin Health

Milk thistle is sometimes used to treat skin conditions including mild psoriasis.¹⁴ It’s also proven useful in treating skin that’s been damaged by radiation during breast cancer treatment.

Milk thistle products appear to help the skin heal from damage caused by UVB radiation from the sun and may offer benefits in preventing non-melanoma skin cancers.¹⁵ In some cases it may be useful in treating these cancers, but studies have yet to fully demonstrate the safety and efficacy of milk thistle use.

Bone Health

Some researchers have suggested milk thistle benefits when treating osteoporosis after menopause, and it’s a commonly used supplement in the U.S. There’s limited evidence, though, for the role of milk thistle in bone health.¹⁰

However, one area of milk thistle research focuses on how it affects bone marrow, which contributes to overall bone health but also has implications in treating diseases like multiple myeloma, a type of blood cancer.

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:¹⁷⁵

Nausea, diarrhea, gas and other digestive symptoms
Headache
Skin reactions (rash, eczema, pruritus)
Joint pain

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.

Milk Thistle and Anaphylaxis

Milk thistle can cause severe allergic reaction and anaphylaxis, a rare but potentially life-threatening allergic reaction.¹⁸ If left untreated, anaphylaxis can lead to shock, coma, cardiac or respiratory failure, or even death. Call 911 or seek help right away if you experience severe side effects from taking milk thistle.

Are There Risks of Taking Milk Thistle?

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.¹

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

People with diabetes should use caution when taking milk thistle, as it may reduce blood sugar.¹

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.¹⁹

How Much Milk Thistle Should I Take?

More research is needed before a standard dosage of milk thistle can be recommended, so check with your healthcare provider. Silymarin, a milk thistle element, is reported safe at doses of 700 milligrams three times a day for 24 weeks.²⁰ It is possible to take too much, and liver toxicity has been observed in people with cancer taking silybin at very high doses (10 to 20 grams per day)

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.

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