Milk Thistle: Trusted Support for Health & Healing in a Toxic World

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Milk thistle is well known for its long history of use as a natural liver detoxifier and protectant. And now a large body of research provides a scientific understanding of its many benefits for humans (and their pets) in an ever-more-toxic world.

Extract of milk thistle has been used for more than 2,000 years as a staple of traditional medicine for those with liver and gallbladder disorders.

The first known mention of milk thistle in this respect was by Theophrastus, a colleague of and successor to Aristotle, in the 4th century B.C. Then, in the 1st century A.D., Roman naturalist Pliny wrote that milk thistle was excellent for “carrying off bile,” meaning that it supported a restoration of impaired liver function – a claim that has since been justified by many modern researchers.

Today milk thistle is one of the most well-studied and commonly-used beneficial plants in the world. The U.S. National Library of Medicine and the National Institutes of Health (NIH) have catalogued more than 400 scientific studies of milk thistle and its active compounds.

Milk thistle also enjoys the distinction of being one of the very few traditional herbs that has been widely accepted by conventional science to have significant “medicinal” value.

But what do we mean when we talk about milk thistle, and why is liver support so important?

What is Milk Thistle?

Milk thistle (Silybum marianum) is a plant in the aster and daisy family of flowers. It grows to a height of 4 to 10 feet and has reddish-purple flowers and large prickly leaves with white markings. The milk thistle plant gets its name from the milky white fluid that comes from the plant’s leaves when they are crushed. Native to southern Europe, the milk thistle plant has been naturalized throughout North and South America and Australia.

You might call milk thistle a “silly” plant because its active ingredient – used in supplements and found in the seeds – is silymarin (pronounced SILL-ee-MAR-inn). Silymarin is a flavonoid complex that is primarily made up of three “silly” flavonolignans: silybin, silydianin and silychristin. Despite its name, there is nothing silly about silymarin’s many potential health benefits – starting with the liver.

Why the Liver Is So Important

The liver is the body’s largest internal organ and has been described as the third most important organ, following the brain and the heart. It has often been referred to as the body’s toxic waste disposal plant, but the liver actually has multiple jobs, including:

• Controlling infections.

• Removing bacteria and toxins from the blood.

• Processing nutrients, hormones, and drugs.

• Making proteins that regulate blood clotting.

• Producing bile to help absorb fats (including cholesterol) and aid digestion.

A healthy liver – essential for survival – is the only internal organ that is able to regenerate most of its own cells when they become damaged.

However, a number of different diseases and conditions can cause chronic liver damage, which leads to cirrhosis – the formation of scar tissue on the liver. As cirrhosis progresses, the liver becomes less and less able to effectively replace damaged cells. In the end, if the progression of cirrhosis cannot be controlled, it will ultimately be fatal.

The most common causes of cirrhosis are chronic alcoholism and hepatitis, but it can also be the result of prolonged exposure to drugs (including acetaminophen), heavy metals and other environmental and bacterial toxins.

The Science Behind Milk Thistle’s Ability to Support the Liver

Although milk thistle was known to be beneficial for liver problems for many centuries, it wasn’t until 1990 that scientists at a liver pathology institute in Clichy, France finally discovered exactly how milk thistle works to protect the liver. They found that:

• First, milk thistle helps decrease the conversion into more toxic substances of many air-, water- and food-borne chemicals such as carbon tetrachloride;

• Secondly, it acts as a potent antioxidant that inhibits these toxic compounds from damaging healthy liver cells.(1)

Scientific studies describing milk thistle’s ability to support various aspects of liver health abound. Following is a sampling from the hundreds of published studies:

Hepatitis:  Nine studies that focused on chronic hepatitis associated milk thistle supplementation with significant improvement for patients. Outcomes included normalization of liver function (determined by biopsy) and relief of symptoms such as abdominal pressure and bloating, nervousness, weakness and insomnia. It took an average of 30 to 40 days for improvements to be noticeable.(2)

Cirrhosis:  Eleven studies looked at using milk thistle with patients who had cirrhosis of the liver. Some of the effects noted included lower mortality rates, improved liver function (determined by liver function tests), reduction of toxic-metabolic lesions, regression of inflammatory changes, and the relief of symptoms such as abdominal pressure and bloating, insomnia and weight gain.(2)

Alcohol, Drugs and Other Toxins:  Over the years, scientists have found that milk thistle can be effective in helping the body avoid or counteract liver damage caused by a variety of toxins such as alcohol, acetaminophen and other drugs, and environmental and bacterial toxins.(3)

It’s interesting to note that in parts of Europe, physicians often prescribe milk thistle to patients for medicinal purposes, most often when they are taking pharmaceutical drugs known to potentially cause liver problems. And the German Commission E, which studies the safety and efficacy of herbs for the German government, recommends milk thistle supplementation in cases of liver damage due to toxins and cirrhosis of the liver, and as a supportive therapy for chronic inflammation of the liver.

Poisonous Mushrooms:  Some of the most impressive studies related to milk thistle and the liver are those that deal with poisoning from ingesting the lethal Amanita phalloides mushroom, commonly known as the Deathcap mushroom. In two separate case studies, multiple members of a family were poisoned when they ate Deathcap mushrooms. Their conditions continued to worsen until silibinin, one of the components of milk thistle, was added to standard therapy. It was then that each of the family members began to make a rapid recovery.(4,5)

Milk Thistle Shows Promise as an Adjunct to Cancer Therapy

One of the most exciting areas of study involving milk thistle is that of cancer research. For example, a National Cancer Institute report on a randomized clinical trial in children with acute lymphoblastic leukemia found that milk thistle supported a decrease in the harmful effects of chemotherapy on the liver without working against the cancer treatment. The children taking milk thistle needed fewer chemotherapy dose reductions because of side effects than the children who did not take milk thistle.(6)

There is also one case report describing the use of milk thistle in a patient with promyelocytic leukemia who required breaks in chemotherapy due to abnormal liver enzyme levels. During four months of treatment with milk thistle, the patient had normal liver enzyme levels and was able to undergo chemotherapy without breaks.(6)

Don’t Forget Fido and Fluffy

Just as milk thistle promotes liver defense and detoxification in humans, it can provide similar benefits for dogs and cats with hepatitis or other liver disorders. It may also be considered as a possible option for pets with inflammatory bowel disease, diabetes and cancer, or as an aid to healing for dogs and cats undergoing drug therapy.

Before giving milk thistle to your pet, check with your veterinarian to make sure it is an appropriate treatment, to ensure that all of the ingredients are safe for your dog or cat, and to learn the correct dosage based on the animal’s size.

While liquid milk thistle formulas are available for pets, they tend to be more expensive than the capsules intended for humans. It’s fairly easy to open a capsule and mix the appropriate amount of milk thistle powder with your pet’s food.  Although milk thistle does come in a liquid extract for humans, it usually contains a fair amount of alcohol and would not be good for your pet.

Need-to-Know Information

In addition to milk thistle (in the form of silymarin) ProHealth’s Milk Thistle Complex™ is a complete liver support formula, which includes choline and inositol to promote fat and cholesterol metabolism and vitamins C and E for improved antioxidant protection.

Dosage:  For adults, the recommended dosage of ProHealth’s Milk Thistle Complex is one capsule, one to four times a day with meals, or as recommended by your healthcare professional.

Side Effects:  Milk thistle has a very good safety record. No toxicity has been reported following even high doses of milk thistle. Several large, carefully designed studies in patients with liver disorders have found that taking milk thistle may rarely result in a mild, short-lived laxative effect or cause nausea, heartburn, or stomach upset.  At high doses (more than 1,500 milligrams a day), mild allergic reactions have occasionally been seen.

Contraindications:  (1) Milk thistle can reduce the effectiveness of oral contraceptives.  (2) Although milk thistle has been used in pregnant women who have a bile blockage in the liver, with no toxic effects to the patient or fetus, if you are pregnant or nursing, it is always best to consult with your healthcare professional before taking any medication or supplement.


Milk thistle has a very long history as a safe and beneficial option for promoting liver health. It is best known for its ability to help protect the liver from the onslaught of toxins we face daily in the form of medications, alcohol, bacteria and the environment. Newer research is finding that milk thistle may also have value as a potential adjunct therapy for various types of cancer.

* Supplement research reporter Karen Lee Richards is HealthCentral’s Health Guide specializing in Fibromyalgia and ME/CFS (



1.  Lettéron P, et al. “Mechanism for the protective effects of silymarin against carbon tetrachloride-induced lipid peroxidation and hepatotoxicity in mice. Evidence that silymarin acts both as an inhibitor of metabolic activation and as a chain-breaking antioxidant.” Biochem Pharmacol 39 (12): 2027-34, 1990.

2.  Buhner, S. H. (2000). Herbs for Hepatitis C and the Liver. (p. 39). United States: Versa Press.

3.  Abenavoli L, et al. “Milk thistle in liver diseases: Past, present, future.” Phytother Res. 2010 Oct;24(10):1423-32.

4.  Carducci R, et al. [“Silibinin and acute poisoning with Amanita phalloides”] Minerva Anestesiol. 1996 May;62(5):187-93.

5.  Hofer JF, et al. [“Treatment of Amanita phalloides poisoning with silybin in combination with penicillin and cortisone”] Wien Klin Wochenschr. 1983 Apr 1;95(7):240-3.

6.  “Questions and answers about milk thistle.” (2012, March 23). National Cancer Institute. National Institutes of Health.


Note: This information has not been evaluated by the FDA. It is general information, is not meant to prevent, diagnose, treat or cure any illness, condition or disease, and should not take the place of the personal attention of a healthcare professional. It is very important that you make no change in your healthcare plan or health support regimen without researching and discussing it in collaboration with your professional healthcare team.

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