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What Is Milk Thistle? | Benefits, Side Effects & Dosage

By Christopher Tack | Clinical Specialist Physiotherapist

Milk thistle (in Latin named Silybum Marianum)  has been used across Europe since the first century and has even been documented in historical texts including the works of Pliny the Elder, a Roman historian and author who wrote the first encyclopaedia of natural history (1). This plant’s leaves, flowers and roots have been eaten as a vegetable, and its seed-like fruits have been consumed for hundreds of years as a coffee alternative.

However now it seems to make a resurgence in popularity as a health aid. This article will examine the scientific theory supporting its benefits and help you decide whether it is worth adding to your health regime.

What Is Milk Thistle?

Milk thistle is a tall herb which grows to approximately 10 feet high in various corners of the globe, including Southern and Western Europe, South America and the Eastern United States. It characteristically has large purplish flowers and small hard seed-like fruits (called achenes) which are the source of its medicinal properties.

In fact, the dried seeds contain approximately 1-4% of the flavonoid mixture, silymarin (2). It is these seeds which are used to create the concentrated silymarin extract that has a higher percentage of 65-80% flavonolignans, flavonoids, fatty acids and other natural plant compounds which have various regulatory effects on our metabolism (3).

The most important of these various compounds seems to be silibinin, which was discovered in 1959 and designated the primary active ingredient in silymarin (4-5). As such you will always see the concentration or amount of silymarin and silibinin stated on packets of milk thistle extract.

milk thistle

Milk Thistle Benefits

 The benefits of silymarin have long been recognised in people with liver disorders (6), in fact, it is often considered the gold standard drug to treat liver problems, and milk thistle has long been a traditional herbal alternative for this population (7). Research indicates that silymarin provides both anti-oxidant and chemoprotective benefits for the liver (8-14).

However, its benefits have also been extended through research in its use for the heart, nervous system and kidneys (15-17). We will examine the proposed benefits of silymarin more closely.

Is Milk Thistle An Anti-Oxidant?

It is worth describing why anti-oxidants are so important. We are reliant on oxygen for our survival. However, a by-product of the use of oxygen for metabolism is the formation of reactive oxygen species (ROS) or free radicals, which we use for cellular signalling and homeostasis.

ROS include peroxides, superoxide and hydroxyl radical, which all have negative effects on our body as facilitators of oxidative damage, aging and age-related diseases (18).

milk thistle antioxidant

Of course in order to survive, we have developed specific protective mechanisms to deal with ROS and prevent oxidative stress (19), and it is the presence of natural anti-oxidants in organisms which enable these mechanisms to work.

Silymarin contributes to our oxidative protection in various ways.

These include:

? Directly scavenging free radicals (and in essence removing free radicals from the cellular environment)

? By inhibiting enzymes which allow free radical formation

? By maintaining the electron transport chain during stress conditions

? By activating anti-oxidant enzymes and transcription factors which are responsible for the synthesis of protective molecules (such as thioredoxin and HSP)

? By reducing the inflammatory response through inhibition of NF-?B pathways (which is a protein complex which regulates the immune response). (20).

Based upon these mechanisms there is a vast array of research examining the influence of silymarin in both animals and humans (15-17, 21-22).

For example, experiments in rats demonstrated that a two-week course of silibinin prevented drug-induced lipid peroxidation (23), which is supported by laboratory experiments examining the preventative effect of silibinin on low-density lipoprotein peroxidation (24).

In other experiments, silibinin also showed a significant anti-oxidant protective benefit for rats exposed to chronic iron overload and prevented liver toxicity (25).  In human studies, the anti-oxidant benefits of silymarin have been shown in people with alcoholic cirrhosis by silymarin enhancing the levels of the enzyme superoxide dismutase in both red and white blood cells. This enzyme breaks down the free radical superoxide, as such preventing oxidative cellular damage (26).

Milk Thistle (Silymarin) | Evidence-Based Uses

Liver Disease

As stated earlier, historically the key target of milk thistle supplementation has been the reduction of liver disease. In fact in Europe silymarin is used to manage the impact of various toxins which cause liver damage (27). These would include alcohol, chemotherapy agents and paracetamol (28-30).

In clinical studies the use of silymarin has been shown to facilitate protection against liver damage, and one of the primary attributes of silymarin has been identified are its anti-oxidant functions (31-32).

However, this is not its only benefit. Another key function identified is its reduction of specific liver enzymes which are involved in liver cell damage.

In a large study of 2,637 people with liver disease treatment with a milk thistle extract for 8 weeks resulted in substantial decreases in liver enzymes and a boost in physician satisfaction of treatment in 88% of cases (33).

Similar findings have been found in a number of randomised controlled trials of the same extract in those with the alcohol-induced liver disease over a period of 4 weeks (34-37).

Additionally, milk thistle has further influences in the regenerative capacity of the liver; assists in the formation of new liver cells and provides further cellular protection by stabilising liver cell membranes to prevent toxins moving into the cells (6).  The larger impact of these physiological benefits is the impediment of fibrosis and cirrhosis due to excessive liver inflammation (commonly seen in alcoholism) (38); improved immune function and response to liver damage (39); and significantly reduced mortality (20%) (40-41).

immune system benefits vitamin c

Endocrine function

Both animal and human studies show that silymarin provides a protective benefit for the pancreas in diabetes (42-43).

In experiments with rats exposed induced- diabetes the pancreas was provided protection by silymarin against oxidative stress and sustained levels of glucose whilst inhibiting insulin secretion (42,44).

In human studies with people with alcoholic cirrhosis and insulin-dependent diabetes, milk thistle extract showed significant reductions in mean daily blood glucose, fasting blood sugar, loss of glucose in urine, and insulin needs over 6 months (43,45). Of course, all these factors indicate better glycaemic control and less risk associated with uncontrolled diabetes.

Immune System: Anti-inflammatory

Another benefit of milk thistle is silibinin’ effect on our immune system, therefore its ability for us to fight off infection and inflammation.

For example, in those with alcoholic cirrhosis, a variety of components of the immune system are enhanced when silymarin is provided (46). This includes the transformation of lymphoblasts which are immature white blood cells which can develop into our natural killer cells (lymphocytes) and assist removal of infection agents via our lymphatic system.

Additionally in this population silymarin also induces a significant reduction of lymphocytotoxicity indicating the greater health of the lymph cells and more effective immune system response (46).

In healthy people, silibinin provides similar benefits however notably it is found that milk thistle extract supplementation can increase the motility (movement) of our most potent immune system m white blood cells (leukocytes). This would suggest an enhanced immune response to infection or inflammatory reaction (e.g. through injury) (47).

Antineoplastic: Chemoprevention

A final benefit of milk thistle and its constituent parts are amazingly a chemopreventative effect- which is where it is used to treat cancer.

The predominant amount of research of silymarin and silibinin has been in laboratory experiments with cells (rather than in human test subjects). For example, cancer treatment benefits have been seen in both human and mouse skin, prostate and breast cancer cell lines (48-55).

Additionally, cell protection effects are seen in rodent liver and trachea cells when exposed to carcinogens, and similar protection was seen in human testicular cells (56-57).

Probably most impressively there has also been one documented case study of a 52-year-old man who underwent a biopsy and was diagnosed with the most common form of liver cancer, a malignant hepatoma (58).

Astonishingly, this cancer was seen to spontaneously resolve following the self-medication by 450mg silymarin by the gentleman in question. Now whilst I wouldn’t advise self-medication for known cancer, this does emphasise the truly active health advantageous afforded to you if milk thistle was to become part of your health supplement regime.

Safety & Side Effects

Studies involving several thousand subjects have been unable to show any significant cautions or side effects to consuming milk thistle (59). In fact, the prevalence of side effects are low and generally limited to mild stomach upset (33).

As always caution is always wise in certain populations (e.g. during pregnancy and childhood)- however, it is presumed safe as it has long been consumed as a food source and no negative effects have been reported historically (60).


A range of doses have been described in the literature between 280-800mg of silymarin daily, and the average concentration of silymarin in milk thistle extract is described as between 70-80% (6).

Some studies describe a dosage of 100mg of silymarin three times per day as the supplements absorption is seen to be optimal with this regime (61). As such most recommendations suggest 100-200mg three times daily alongside your meals (62-63).

Take Home Message

Often when you delve into the scientific theory surrounding herbal supplements you find yourself wanting. Sometimes the natural remedy gurus will overestimate the impact of some herbal supplements, however this is not the case for milk thistle.

Historical use and scientific backing are in favour of the use of this herb as an anti-oxidant and cellular protective agent. Two good reasons to consider its use in your daily nutrition regime.

Our articles should be used for informational and educational purposes only and are not intended to be taken as medical advice. If you’re concerned, consult a health professional before taking dietary supplements or introducing any major changes to your diet.


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