Milk thistle (Silybum marianum), also known as St Mary’s thistle or holy thistle, is a flowering herb with a vibrant purple flower, spiny stems, brown spotted fruit and shiny black seeds. It is native to the Mediterranean region, however is now found throughout the world. Milk thistle has been used for the past 2000 years as a herbal remedy for a variety of ailments. Originally it was used for snakebites and melancholy, and more recently has been used for ailments relating to the liver, spleen and kidney among others.


The active ingredient in milk thistle is known as silymarin, a chemical extracted from the seeds. Silymarin is part of a group of flavonoids (silibinin, silidianin, and silicristin), which has antioxidant and anti- inflammatory properties. It is believed to protect the liver from toxins by helping repair liver cells (hepatocytes) damaged by alcohol and other toxic substances and keeps new liver cells from being destroyed by these same toxins.


Studies have shown that it can protect hepatocytes from long-term damage caused by toxins such as chemotherapy drugs, alcohol and paracetamol. Further, hepatitis and other conditions that damage the liver cause a hardening or fibrosis, which negatively impacts liver function. Milk thistle has been found to reduce this fibrosis.


Most milk thistle products are standardised preparations made from the seeds of the plant. Most preparations are standardised to contain 70 - 80% of silymarin. Preparations available that include milk thistle include Blackmores Milk Thistle, Australia by Nature Liver Tonic, Beetox Liver Tonic and Liver Mate.


Like all herbs or supplements, milk thistle can trigger side effects and can interact with other herbs, supplements, or medications. Milk thistle is generally regarded as safe. One consideration with this safe herb is it may hinder iron absorption from food, so don’t have it at the same time as iron-rich meals such as meat and green leafy vegetables. Side effects are usually mild and may involve a stomach upset and diarrhoea. Pregnant and breast-feeding women; people with a history of hormone-related cancers; and people with an allergy to ragweed, chrysanthemums, marigolds, chamomile, yarrow, or daisies should not use milk thistle. As with all herbs and supplements, milk thistle should be taken under the supervision of a health care professional.