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August 4, 2021


Michael Kuefner, PhD (BMS)
Milk Thistle – A Promising Herbal Supplement For Liver Health

Fact Checked By Michael Kuefner, PhD (BMS)
 August 4, 2021

Milk Thistle

‘Liver health’ is a term tossed around quite often in the supplement industry, oftentimes with no description or characterization.

But what exactly does liver health or liver support refer to?

Most commonly, improvements in liver health refer to protection and/or treatment of the most common liver diseases in the modern day.

These diseases include (1):

  • Viral hepatitis
  • Alcoholic liver disease
  • Nonalcoholic liver disease (NAFLD)
  • Cholestasis
  • Drug-and toxin-induced liver disease
  • Primary liver malignancies


Liver illnesses are caused by numerous issues - inflammation, elevated levels of dietary cholesterol or fats, viruses, drug-induced injuries, and more.

The prevalence of NAFLD alone in western countries ranges from an astounding 20-30% (2).

And while some therapies and medications are effective in mediating these diseases and their symptoms, other avenues are being explored and tested to enhance protection, treatment, and overall liver health.

This is where Milk Thistle comes in, a herbal remedy which has been used for hundreds of years by naturopaths, herbalists, and physicians to treat liver diseases and prevent from environmental toxins.

Where does it come from?

Milk thistle is native to Europe and was introduced in North America by colonists.

Now, it is found in the eastern USA, California, South America, Africa, Australia, and Asia.

Derived from the milk thistle plant, Milk Thistle is also known as Silybum marianum.

Silybum marianum is a prickly plant, characterized by distinct purple flowers and white veins – a feature legends say was caused by a drop of the Virgin Mary’s milk falling onto its leaves.

What’s in this Milk Thistle, anyway?

The major active compounds responsible for Milk Thistle’s beneficial effects (we’ll get to those, don’t worry!) are silymarin and silybin, two flavonolignans extracted from the plant itself (3).

‘Milk Thistle’ and silymarin are used interchangeably in the literature.

Since the discovery of these two natural bioactive compounds, major pre-clinical and clinical research studies have tested their efficacy in treating liver-related diseases.

While not approved or recommended by the US Food and Drug Administration at this time, millions of people consume Milk Thistle today (4).

Milk Thistle Benefits for Liver Health?

Studies since the early 1990’s indicate that Milk Thistle may improve liver function and provide liver support in a variety of ways, such as (4):

  • Providing antioxidant defense
  • Anti-inflammatory capabilities
  • Antifibrotic substance
  • Acting as a ‘Toxin blockade’

Antioxidant Defense

Natural compounds such as Milk Thistle have displayed promising results in pre-clinical trials in treating NAFLD (5).

This benefit is likely due to Silymarin’s natural antioxidant capabilities in the liver, which entail a few mechanisms:

  • Inhibit enzymes that produce free radicals, in order to prevent free radical formation (typically known as reactive oxygen species)
  • Scavenging free radical actions to prevent oxidative stress
  • Iron (Fe) and Copper (Cu) chelation in the intestines
  • Increased synthesis of molecules (heat shock proteins, thioredoxins) that protect the liver from stressful stimuli (oxidative stress)
  • Activation of antioxidant molecules that prevent or dramatically reduce damage in the liver
  • Superoxide dismutase has beneficial, potent antioxidant activity and is activated/increased by Milk Thistle (6).

Anti-inflammatory Capabilities

Similar to its antioxidant features, studies have shown Milk Thistle is effective at decreasing autoimmune and immune-mediated liver diseases.

This feature is possibly due to its ability to suppress immunotoxicity and T-cell function (7).

Milk Thistle displays potent anti-inflammatory action in rodent models of liver disease, such as fatty liver disease, stress-induced liver syndromes, and liver injuries.

Other studies suggest Milk Thistle may suppress liver inflammation by reducing cytokine release, mainly a very common cytokine known as tumor necrosis factor-α (TNF-α) (8).

In a model of liver steatosis (fatty liver disease, NAFLD), a recent study in 2018 showed that mice treated with Milk Thistle had significantly reduced liver inflammation.

This was due to the compound preventing activation of a primary inflammatory pathway of the liver (9).

Antifibrotic Activities

When cells in the liver, also known as hepatocytes, get injured, the result is liver fibrosis – a serious disease that afflicts many individuals today.

It is associated with hepatic insufficiency and hypertension, and is characterized by elevations in collagen and pro-collagen.

Recent rodent experiments show that treatment with Milk Thistle can inhibit the initial process of liver fibrosis in response to liver injury, as well as progression of the disease.

These studies displayed that Milk Thistle reduced collagen and pro-collagen III levels by 30% following liver injury in order to inhibit fibrotic processes (10).

The anti-fibrotic observations by Milk Thistle have also been observed in other recent studies on rats.

Milk Thistle as a ‘Toxin Blockade’

The ‘death cap’ mushroom, also known as Amanita phalloides has a lethal dose of 0.1 mg/kg body weight in humans.

Interestingly, for years naturopaths have stated that intravenous Milk Thistle administration in patients poisoned with toxic mushrooms can save their lives.

While for obvious reasons clinical trials on this topic do not exist, case reports and uncontrolled trials do reiterate this function, indicating that Milk Thistle can effectively block the toxic effect of some of these substances (11).

What About Side Effects?

Although somewhat modest and variable, side effects have been reported by individuals taking Milk Thistle or silymarin compound, including:

  • Allergic reactions – more common in people who are allergic to plants from similar families (ragweed, daisies, marigolds)
  • Gastrointestinal issues – diarrhea, constipation, nausea
  • Itchiness
  • Headaches

Some Concluding Remarks – Take it, or Not to Take it?

While somewhat controversial due to the lack of robust clinical studies on the effect of Milk Thistle in humans, the herbal supplement seemingly has numerous benefits with respect to liver health and support with little side effects.

The compound has proven antioxidative and anti-inflammatory effects in the body, both of which are involved in preventing and/or treating a bevy of liver diseases.

Altogether, this provides some context for the benefits of Milk Thistle for improved liver health.

While more scientific studies need to be done to understand it’s efficacy, it does appear to have a valuable role in the liver- if you suspect you may be at risk for liver damage or liver diseases, Milk Thistle may be one potential therapy to mitigate these pathologies.