Milk Thistle: Presentation, Indications, Mechanism of Action, Dosage, Side Effects, Warnings, Contraindications and Interactions

The mixture of the extract of the seeds of the Silybum marianum plant contains Silymarin, a complex of flavonoids.

Milk thistle (Silybum marianum) is a herbal supplement used to treat liver and biliary disorders.

Silymarin is the active component that protects liver and kidney cells from the toxic effects of drugs, including chemotherapy.

Although milk thistle has not significantly altered the course of chronic liver disease, it has reduced liver enzyme levels and demonstrated anti-inflammatory and T-cell modulating effects.

There is strong preclinical evidence for the hepatoprotective and anticancer effects of Silymarin, including inhibition of the growth of human cancer cells in cells of the prostate, skin, breast, and cervix.

This is a plant that belongs to the Compositae (daisy) family. It has glossy green leaves with spines on the edges and characteristic buds of large purple flowers.

This plant, native to the Mediterranean, is grown in many parts of Europe.


Over the years, some confusion has been created about the terminology of this plant; it was first known as Carduus marianus. Today, most phyto-therapists prefer to use the botanical name Silybum marianum.

This plant has many famous names, with Cardo Mariano and Cardo de Santa María being the most common.

Milk Thistle has a long history as a medicinal plant.

In the 19th century, the German physician Rademacher was very interested in the activity of this plant and treated all his patients with liver problems using a dye made from the seeds of the plant.

This dye is still found today in some Pharmacies and is known under Rademacher’s tincture.

Active ingredient

Milk thistle extract, which is the most common form of the supplement, has in its composition:

  • From 65 to 80% silymarin (concentrated from 1.5 to 3% of the plant).
  • Approximately 20 to 35% of fatty acids (60% linoleic, 30% oleic, and 9% palmitic).


Milk thistle is sold in oral capsules, tablets, powder, and liquid extract. People primarily use the supplement to treat liver conditions.

Indications of milk thistle

Research on using milk thistle for specific conditions shows:

In diabetes

Milk thistle might lower blood sugar in patients with type 2 diabetes.

Indigestion (dyspepsia)

Milk thistle, in combination with other supplements, may improve indigestion symptoms.

Liver diseases

Research on the effects of milk thistle on liver diseases, such as cirrhosis, hepatitis C, and gallstones has shown mixed results.

Clinical data has confirmed that milk thistle is essential in treating chronic and acute hepatitis.

The symptoms of liver diseases that we observe when functioning below its capacities, such as poor appetite and fatigue, have been clinically shown to improve with this plant.

The plant is also beneficial for treating fatty liver and has shown promising results with liver cirrhosis.


Milk thistle is also used in digestive problems like slow and difficult digestion, poisoning, and flatulence.

Mechanism of action

Only recently was the active principle of Milk Thistle isolated. It is a flavonol, previously unidentified and given the name Silymarin.

Phytotherapy researchers Wagner, Hoerhammer, and Munster were the first to describe this component, identifying it as the anti-hepatotoxic principle in the plant.

Since then, the published literature on this plant confirms that, clinically, the most crucial use of this plant is to protect the liver against damage.

The liver deals with many toxins every minute of the day in its regular activity.

Some of these toxins (as described in acetaminophen poisoning) can cause liver damage.

Silymarin is now known to be able to prevent or may strengthen the area before damage occurs, possibly by stabilizing the liver cell membrane so that toxins are unable to reach it.

Some research also indicates that Silymarin can reverse damage to hepatocytes that have already occurred.

Silymarin is likely to increase cellular protein synthesis levels, helping damaged cells recover and synthesize essential metabolites such as the antioxidant glutathione.

The action of Mariano broth in the body is cholagogue, digestive, detoxifying, and hepatoprotective.

It can increase the rate of protein synthesis in liver cells and promote subsequent repair after cell injury.

The exact mechanism is unknown, but it is believed to be due to RNA polymerase I and ribosomal RNA activation in some way.


Taking 420 mg of milk thistle a day (standardized to 70% silymarin) in divided doses is safe for up to 41 months. Beyond that period, use is not recommended.

Side effects of milk thistle

Milk thistle is considered safe and well-tolerated; the only adverse events are reported when taken within the recommended dose range.

Research has revealed gastrointestinal disorders such as diarrhea, bloating, gas, and an upset stomach with a mild laxative effect.

Oral ingestion of milk thistle has also been linked to abdominal fullness (or abdominal pain), anorexia (loss of appetite), and changes in bowel habits.

An allergic reaction is rare; milk thistle can cause allergic reactions in people, especially those allergic to ragweed, marigolds, daisies, and chrysanthemums.

Specific reports also state that milk thistles can cause skin rashes, hives, and eczema.

Skin rashes caused by milk thistle are due to IgE antibodies that raise histamine levels in the skin, leading to the condition.

You may experience weakness, a tingling sensation in the muscles, and muscle cramps.

As you ingest the herb, your immune system reacts to it as dangerous, creating a defense mechanism against the supplement.

Warnings and Contraindications

Milk thistle is known to have several estrogen-like properties, and specific sources say it could worsen some health conditions like estrogen-sensitive endometriosis, where endometrial tissue appears outside the uterus and causes pain.

Milk thistle can also lower hormone levels in the body, so taking it along with estrogen pills could reduce their effectiveness.

Some estrogen pills include equine estrogens, Ethinyl estradiol, and estradiol.

If the patient has breast cancer, uterine cancer, ovarian cancer, endometriosis, or uterine fibroids, avoiding milk thistle for its estrogenic effects should be considered.

Milk thistle might interact with statin-containing medications, known to lower cholesterol levels (lower lipids).

These medications include Mevacor, Lescol, Zocor, Pravachol, and Baycol.

Both milk thistle and these drugs are broken down by liver enzymes.

In patients with diabetes, milk thistle should be used with caution, as the supplement may lower blood sugar.

Milk thistle can cause an allergic reaction, including a severe and life-threatening reaction (anaphylaxis).

Milk thistle is not recommended during lactation and pregnancy, as there is no related research in humans.

Milk thistle interactions

Cytochrome P450 2C9 (CYP2C9) substrates

Taking milk thistle could affect this enzyme and the medications it processes, such as diazepam (Valium), warfarin (Coumadin, Jantoven), and others.

Medications for diabetes

Milk thistle might lower blood sugar in people with type 2 diabetes.

Taking milk thistle with diabetes medications can cause additive effects. Blood sugar levels should be closely monitored.

Metronidazole (Flagyl)

Milk thistle could reduce the effectiveness of this antibiotic. The use of milk thistle and metronidazole together should be avoided.

Simeprevir (Olysio)

Taking milk thistle with this hepatitis C medicine may increase the medicine levels in your blood plasma. The use of milk thistle and simeprevir together should be avoided.

Sirolimus (Rapamune)

Taking milk thistle with this immunosuppressant could change how your body processes the medicine.