Milk thistle and silymarin: does it help the liver, how to take it and who should avoid it

What milk thistle and silymarin are

Milk thistle is a prickly plant with large purple flowers from the daisy family. Its fruits (often called seeds) are used medicinally. The main active part of the extract is silymarin, a mixture of compounds. Of these, silibinin is the best studied.

Historically, people took milk thistle for liver problems and to increase breast milk. Today it’s sold for the liver, diabetes and “detox”. On iHerb you’ll find:

• crushed or powdered fruits – for tea or in capsules;
• standardised extract – with the silymarin content stated in milligrams;
• “liver support” and detox blends – milk thistle alongside other herbs.

Milk thistle for liver health: what the trials found

Milk thistle has been studied in many liver conditions. NCCIH sums it up: results have been conflicting or too limited to draw conclusions.

In the Cochrane review, liver-related deaths were lower when all trials were pooled. But the effect disappeared in the high-quality trials, and the authors say their results question any benefit of milk thistle.

The hepatitis C trial tested higher than usual doses: 420 or 700 mg of silymarin three times a day for 24 weeks. Only 2 people in each group reached the target fall in the liver enzyme ALT, on silymarin and on placebo alike. Viral load and quality of life didn’t change either.

Milk thistle for a fatty liver

Fatty liver disease (NAFLD, now also called MASLD) is the commonest reason people look for a “liver supplement”. In a US trial, 78 people with fatty liver inflammation took 420 or 700 mg of silymarin three times a day for 48 weeks. Their liver biopsies didn’t improve significantly compared with placebo.

The NHS says healthy lifestyle changes are the main treatment for fatty liver disease: a balanced diet, at least 150 minutes of exercise a week, losing weight if needed, no smoking and no more than 14 units of alcohol a week. If it has progressed to fibrosis or cirrhosis, a liver specialist manages treatment.

Milk thistle detox: why “cleansing” isn’t a reason to take it

Your liver clears and processes substances by itself, without a “cleanse”. No trials show that milk thistle detoxes a healthy person’s liver.

Detox blends carry a practical risk too. Memorial Sloan Kettering describes a man on warfarin whose INR (a blood clotting measure) rose from 2.64 to 4.12 after a liver cleanse supplement containing milk thistle. It returned to normal when he stopped. With multi-herb detox mixes, it’s harder to know what you’re actually taking.

Mushroom poisoning: a hospital drug, not a capsule

For death cap mushroom poisoning, hospitals sometimes give silibinin into a vein alongside other treatment. A review of 877 cases over 40 years found 90% survival with silibinin, compared with 59% with supportive care alone. In cases where the toxin was confirmed, though, the difference wasn’t statistically significant.

Milk thistle capsules are no substitute. If you develop vomiting, stomach pain or diarrhoea after eating wild mushrooms, call 999 straight away and keep any leftover mushrooms.

How to take milk thistle

The European Medicines Agency (EMA) accepts milk thistle as a traditional herbal medicine for indigestion, a feeling of fullness and to support liver function, once a doctor has ruled out serious disease. This means it has a long record of safe use, but not enough clinical proof that it works.

EMA doses for adults, taken before meals:

Pick the form you have in your hand or are looking at on iHerb:

See a doctor if symptoms last more than 2 weeks or get worse. If you notice yellowing skin or a change in the colour of your urine or stools, go straight away.

How long can you take milk thistle?

There’s no standard course. EMA guidance works on 2 weeks: if indigestion or fullness hasn’t settled by then, look for the cause rather than carrying on. Liver trials gave silymarin for 24–48 weeks with no more serious side effects than placebo. But they found no benefit either, so long-term use “just in case” makes little sense.

Side effects and who should avoid milk thistle

By mouth, milk thistle is usually well tolerated. Common side effects include bloating, nausea, wind, an upset stomach and diarrhoea, and less often headache. NCCIH also flags quality problems: some products contained much more or less silymarin than stated, and some held pesticides or mycotoxins.

Don’t take milk thistle if:

• you’re allergic to the daisy family – ragweed, chamomile, chrysanthemum, marigold. Rash, hives, asthma attacks and anaphylaxis are possible;
• you’re pregnant or breastfeeding – safety hasn’t been established and the EMA doesn’t recommend it;
• you’re under 18 – there isn’t enough data.

Interactions to mention to your doctor or pharmacist:

• sirolimus after a kidney transplant – milk thistle may slow its clearance;
• warfarin – a rise in INR has been reported;
• haloperidol and risperidone – cases of pancreatitis have been reported with the combination;
• diabetes medicines – milk thistle may affect blood sugar, so monitor your levels;
• other medicines processed by the liver – in lab studies silymarin affected the CYP3A4 and UGT enzymes, though human data conflict.

If you take several products, check our compatibility chart. For another popular herb with liver risks, read our guide to turmeric and curcumin.

How to choose milk thistle on iHerb

1. Get your liver blood tests done and ask your GP whether milk thistle makes sense for you.
2. Rule out the warnings: daisy-family allergy, pregnancy, interacting medicines.
3. Choose plain milk thistle rather than a detox blend with a dozen herbs.
4. Check the silymarin in mg on the label and compare the dose with the table above.
5. Prefer products with independent quality testing, since contaminants have been found in milk thistle.

More supplements for digestion are collected in our gut health section. Not sure what you need? Start with our vitamin check.