Milk thistle is well known as a liver herb that is safe for all to use to support this important detoxification system. It works via a direct stimulating effect on the liver, which also encourages the flow of bile. Milk thistle is also both a restorative and protector of the liver. It encourages optimum function of the liver and gall bladder – offering a wide range of therapeutic benefits such as better detoxification of the blood as well as improving the assimilation of fat-soluble nutrients.

Milk thistle’s protective and rejuvenating effect on liver cells has been well documented in modern research. This includes support where there has been exposure to high levels of chemicals and pollution, whether through diet, medication or unprotected contact.

As the name alludes in the ‘Doctrine of Signatures’ milk thistle is used as a galactagogue- to enhance the flow of breast milk and care for the young. The ‘milky’ white veins are a helpful ‘sign’ and a pointer of its benefits.

Milk thistle is also a useful remedy for dyspepsia and digestive complaints of that are associated with a sluggish liver, after serious conditions have been ruled out (3).

Milk thistle has a sweet, warming and nourishing action. Due to its milder bitter flavour it is useful for those with a colder constitution or for people who are depleted and require nourishing restorative support alongside detoxification. Milk thistle’s warming energetics also have a decongestant effect on stuck and stagnant blood flow resulting from its ability to reduce and eliminate toxicity from the blood (8).

Matthew Wood recommends it for people with dry constipation that is relating to liver congestion and lack of bile. This type of constipation will usually present as hard and small (rabbit droppings) or they may also be pale in colour due to lack of bile. They might also float rather than sinking, which can indicate poor fat absorption (8).

Milk thistle has been used for more than 2000 years for diseases of the liver and gallbladder (4). In Europe, milk thistle was used traditionally for curing jaundice and for inflammation in the biliary ducts. It was also traditionally used for hepatitis and haemorrhoids (1).

Dioscorides referred to milk thistle as a remedy for venomous snake bites, whilst Culpepper discusses an infusion made with both the seeds and root for disintegrating and expelling gall stones (1).

Traditionally, milk thistle was used by nursing mothers for increasing milk production. As a bitter tonic, it has also had a long history of use for supporting the digestive system. It is referenced also as a demulcent to reduce inflammation topically and as an antidepressant and for dyspeptic complaints (4).

Digestive system

Some of the primary uses for milk thistle are centred around the liver gall bladder and its associated systems. Herbalists may use milk thistle as a part of a supportive treatment for all manner of liver diseases including for cirrhosis, fatty liver, hepatitis and other liver function abnormalities (1). Milk thistle is also indicated for liver problems that may occur in relation to medicines, chemical exposure or environmental pollutants (1).

A number of mechanisms have been identified as being involved in milk thistle’s effects on the liver. It works by stabilising and protecting the hepatocyte membrane against injury, as well as regulating its permeability (1). It has also been shown to increase the proliferation of important liver cells called Kuppfer cells (which are involved in the breakdown of blood cells in the liver) (11).

Metabolic

Milk thistle has potent free radical scavenging properties. It is used to improve detoxification mechanisms and improve cellular regeneration (1). Milk thistle is also indicated in a number of conditions that are caused by oxidative stress and where there has been exposure to pollutants, chemicals are other toxins (1). 

Milk thistle may also sometimes be applied for treatment and prevention of blood sugar conditions such as diabetes. It may be most relevant for use where liver conditions are accompanied by a diabetic predisposition or to help lower blood glucose levels in diabetes type 2 patients alongside conventional treatment (7).

Milk thistle can be used to support phase 1 and phase 2 detoxification pathways. The phase 1 pathway attempts to break down compounds for excretion via oxidation, hydrolysis or reduction reactions facilitated by the cytochrome P-450 enzyme system. If that doesn’t work, the compounds go into phase 2 where other molecules (such as cysteine, glutathione, or sulphur) are added to make the initial compound suitable for excretion. It is then excreted through the bile into the bowel or eliminated as water-soluble compounds via the bladder (9).

There are a fair number of high-quality clinical trials on milk thistle. Most studies have investigated the isolated compound silymarin or its most active isomer silybin, rather than the herbal plant in its whole form. A number of these studies have been included below to demonstrate the evidence base for the medicinal actions discussed in this monograph.

Most studies have been carried out on extracts that contain between 60-80% silymarin (1). Many trials using the standardised extract of milk thistle support the clinical indications for both non-alcoholic and alcoholic fatty liver disease/ damage as well as for cirrhosis, fatty liver, exposure to chemical pollutants (such as drugs, halogenated hydrocarbons, solvents, paints, glues and anaesthesia) and even for the treatment of death cap poisoning (1).

A review of clinical studies evaluating the safety and efficacy of milk thistle

In this review, a number of experimental and high-quality clinical studies confirmed a number of effects such as anticancer, antidiabetic, and cardioprotective properties of milk thistle extracts. Milk thistle also has a strong body of evidence for mechanisms by which it protects the liver against toxins as well as for its ability to therapeutically assist in chronic liver diseases (3).

Meta-analysis and systematic review of milk thistle for the treatment of liver disease

A systematic review of available literature was carried out to determine the efficacy and safety of milk thistle for the treatment of liver disease. The fourteen trials included in this review support the use of milk thistle in the treatment of liver disease (5).

The therapeutic potential of milk thistle in diabetes

A review was carried out to analyse the available literature surrounding the use of milk thistle for blood sugar abnormalities such as diabetes. Numerous studies showing milk thistles efficacy were included in this review, including human studies, in vitro and in vivo studies. Compounds of milk thistle, namely silibin have been shown to produce beneficial effects on several diabetic complications, including diabetic neuropathy, diabetic nephropathy, and non-alcoholic steatohepatitis. These effects are thought to be mainly in relation to the anti-oxidant properties of milk thistle (7).

There is a group of polyphenols called flavolignans, which one of the main compounds of milk thistle silymarin is a part of. These have a protective and rejuvenating effect on liver cells, so much show that it has been shown to neutralise the toxic effects of one of nature’s most poisonous mushrooms — amanita phalloids. This mushroom is known as ‘the avenging angel’, and produces the liver-destroying alkaloids amanantine and phalloidine. A treatment has now been developed into an injectable form for acute poisoning (3).

Milk thistle is native to the Mediterranean region. It is mostly found in disturbed areas, such as pastures, roadsides, ditches, and fencerows.

According to the IUCN Red List of Threatened Plants Status milk thistle is classified as least concern due to stable populations in most of its native habitats (9).

Habitat loss and over-harvesting from the wild are two of the biggest threats faced by medicinal plant species. There are an increasing number of well-known herbal medicines at risk of extinction. We must therefore ensure that we source our medicines with sustainability in mind. 

The herb supplement industry is growing at a rapid rate and until recent years a vast majority of medicinal plant produce in global trade was of unknown origin. There are some very real and urgent issues surrounding sustainability in the herb industry. These include environmental factors that affect the medicinal viability of herbs, the safety of the habitats that they are taken from, as well as the welfare of workers in the trade.

The botanical supply chain efforts for improved visibility (transparency and traceability) into verifiably sustainable production sites around the world are now certificated through the emergence of credible international voluntary sustainability standards (VSS). 

Read our article on  Herbal quality & safety: What to know before you buy and Sustainable sourcing of herbs to learn more about what to look for and questions to ask suppliers about sustainability.

Herbal Medicines are often extremely safe to take, however it is important to buy herbal medicines from a reputed supplier. Sometimes herbs bought from unreputable sources are contaminated, adulterated or substituted with incorrect plant matter.

Some important markers for quality to look for would be to look for certified organic labelling, ensuring that the correct scientific/botanical name is used and that suppliers can provide information about the source of ingredients used in the product.

A supplier should be able to tell you where the herbs have come from. There is more space for contamination and adulteration when the supply chain is unknown.

Milk thistle can be grown as a winter annual or a biennial which means that it dies once it has flowered and produced seeds. However, it usually self-seeds in the vicinity, so take care to keep the plants under control 

Either sow seeds in early spring for late summer flowering, or sow in late summer for flowering in early summer the following year. Either way, as these are large seeds that germinate and grow quickly, we recommend sowing the seeds directly into pots (rather than trays) – one seed per pot.

If you sow in the spring, sow indoors and plant out as soon as they are big enough to handle. Space the plants at least 2-3 feet apart and allow plenty of space for paths (the spiky leaves will stop all traffic on your paths if you don’t). If you sow in late summer, sow outdoors and move the pots indoors for the winter, then plant out the following spring. Late summer sowing normally produces higher seed yields.

1. Bone, K. (n.d.). Principles and practice of phytotherapy : modern herbal medicine. Elsevier Uuuu-Uuuu.
2. (No date) European Union herbal monograph on Silybum Marianum (L.) gaertn., fructus. Available at: https://www.ema.europa.eu/en/documents/herbal-monograph/draft-european-union-herbal-monograph-silybum-marianum-l-gaertn-fructus_en.pdf (Accessed: 18 December 2023). 
3. Saller, R., Brignoli, R., Melzer, J., & Meier, R. (2008). An Updated Systematic Review with Meta-Analysis for the Clinical Evidence of Silymarin. Forschende Komplementärmedizin / Research in Complementary Medicine, 15(1), 9–20. https://doi.org/10.1159/000113648
4. Milk Thistle (PDQ®)–Health Professional Version – National Cancer Institute. (2003, December 23). www.cancer.gov. https://www.cancer.gov/about-cancer/treatment/cam/hp/milk-thistle-pdq
5. Saller, R., Brignoli, R., Melzer, J., & Meier, R. (2008). An Updated Systematic Review with Meta-Analysis for the Clinical Evidence of Silymarin. Forschende Komplementärmedizin / Research in Complementary Medicine, 15(1), 9–20. https://doi.org/10.1159/000113648
6. DOĞAN, G., KARA, N., GÜR, S., & BAGCI, E. (2022). Chemical Composition and Biological Activity of Milk Thistle Seeds (Silybum marianum (L.) Gaertn.). International Journal of Nature and Life Sciences, 90–98. https://doi.org/10.47947/ijnls.1124453
7. Wood, M. (). The earthwise herbal : a complete guide to Old World medicinal plants. North Atlantic Books.
8. Not for Public Distribution. For Education of Health Care Professionals Only. 1 Herbs for Enhancing Phase I/II Hepatic Detoxification Key Points at a Glance Detoxification in the Liver. (2011). https://assets-us-01.kc-usercontent.com/b3f5510f-b2f6-0081-05a1-dbd7a9328e1f/16b1a3a5-b32a-4fb2-98a7-d5dd8d3d7ae0/2011-pp-no-56_au.pdf
9. Khela, S., & RBG, R. (2019, August 28). IUCN Red List of Threatened Species: Silybum marianum. IUCN Red List of Threatened Species; Name. https://www.iucnredlist.org/species/202991/88329022
10. Rainone, F. (2005). Milk Thistle. American Family Physician, 72(7), 1285–1292. https://www.aafp.org/pubs/afp/issues/2005/1001/p1285.html#:~:text=In%20some%20studies%2C8%20milk