A purple-flowered thistle; its seeds contain silymarin.
Why it’s used: Traditionally used to support liver function.
Milk thistle, Silybum marianum, is a tall, spiny plant with purple flower heads and glossy leaves marked with white veins. It is native to the Mediterranean and now grows wild in many parts of the world, including the UK. Legend links the white markings to drops of the Virgin Mary's milk, which is where the name comes from.
It has been used in European herbal tradition for over two thousand years and is traditionally used to support liver function. The seeds contain silymarin, a group of compounds that includes silybin, the main one researchers study. Milk thistle has been widely researched, but results in people are mixed and it has no authorised health claim.
On labels you will see milk thistle, Silybum marianum seed extract or silymarin, usually with a percentage such as 80% silymarin. That figure is more useful than the total extract weight. Some products bind silybin to phosphatidylcholine, a form designed to help absorption.
3 findings behind this ingredient. Hover a card for the detail and the source.
A meta-analysis of 26 randomised controlled trials with 2,375 people with NAFLD found silymarin reduced ALT, AST, total and LDL cholesterol and triglycerides, and improved fatty liver scores and steatosis on histology.
A meta-analysis of eight randomised placebo-controlled trials found silymarin gave significantly greater reductions in ALT and AST, independent of weight loss. The authors flagged quality concerns in the included studies.
A 24-week double-blind trial randomised 83 adults with MASLD to 103.2 mg silymarin a day or placebo. Silymarin significantly reduced liver stiffness, GGT and ApoB, though most other markers did not change.
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Silymarin is a group of plant compounds extracted from milk thistle seeds, with silybin the most abundant. Supplements are often standardised to around 80% silymarin, which tells you how concentrated the extract is and makes products easier to compare.
People allergic to plants in the daisy family, such as ragweed, chrysanthemum, marigold or daisy, should avoid it. Check with your GP first if you have diabetes, take medicines or are pregnant or breastfeeding.
It may. NCCIH notes interactions are possible and that milk thistle may lower blood sugar, which matters if you take diabetes medicines. If you take any prescription medicine, speak to your GP or pharmacist before starting milk thistle.
Information only, not medical advice. If you take medication, are pregnant or breastfeeding, speak to your GP or pharmacist first.
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