SupplementsHerbs & MushroomsMilk Thistle
Milk Thistle
Silybum marianum, with 80% silymarin extract
A purple-flowered thistle people have used for their livers for centuries, with a long history of use, a good safety record and less proof than you might expect.
- Builds up
- Weeks to months
- In your body
- A few hours
- Per 1 capsule
- 2 ingredients
- 30-day supply
- $9.00One capsule a day, plus packing and delivery
What is milk thistle?
Milk thistle is a tall plant with big purple flowers, native to the Mediterranean and also known as Mary thistle or holy thistle. Early colonists brought it to North America. People have used it as both a food and a herbal remedy for hundreds of years, mainly for the liver.
The compounds people care about are in the seeds. Together they're called silymarin, which is a mix of several related plant compounds rather than a single substance.
Ours combines two forms: a seed extract concentrated to 80% silymarin, and plain milk thistle seed.
What it does
- LiverTraditionally used to support normal liver function.
- AntioxidantProvides antioxidant support.
- Blood sugarMay help maintain blood sugar already in the healthy range.
These statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure or prevent any disease.
What people take it for
MixedLiver enzymesSome studies found lower ALT, one of the liver numbers on a blood test. Others found no real difference, and the overall evidence is shaky.
Early daysBlood sugarA handful of small studies found lower fasting sugar and HbA1c in people with type 2 diabetes. Those studies weren't strong.
MixedBlood fatsIn people with fatty liver, triglycerides fell and HDL rose a little. In people with diabetes, cholesterol didn't change.
How long it takes
It doesn't build up in your blood. Liver studies ran from 4 to 48 weeks, so any change takes a repeat blood test to see, not a feeling.
- 1 to 3 hoursSilymarin reaches its highest level in your blood
- About a dayMost of it has been changed by your liver and sent out through bile
- 4 to 48 weeksHow long liver studies ran, so wait for a repeat test before judging it
How long it stays in your body
Your body changes silymarin quickly. The original compounds halve in 1 to 3 hours, and the versions your liver makes from them in 3 to 8.
What's in a capsule
One capsule holds 250 mg of extract at 80% silymarin, which works out to 200 mg of silymarin, plus 200 mg of milk thistle seed. Studies in healthy people often used 420 mg of silymarin a day, split into three, so one capsule is about half of that.
A compound that heads straight for your liver
Here's what makes silymarin unusual. Very little of it ever gets far into your body. Your gut and liver grab it, change it quickly, and send most of it out through bile, the fluid your liver makes to digest fat. Only about 1 to 5% leaves through your kidneys. So whatever it does, the liver sees far more of it than the rest of you.
This also changes with your health. In people with liver problems, the total amount in the blood was 2 to 5 times higher than in healthy people, likely because a struggling liver clears it more slowly.
Now the honest part. For all its fame, milk thistle hasn't clearly been shown to help liver disease. Two US government-funded studies, one in hepatitis C and one in fatty liver inflammation, found no benefit. A recent large review found lower ALT in some people, by about 7 points, but rated that evidence as very uncertain.
On the plus side, it has a clean record at everyday amounts. Reviews haven't tied milk thistle to liver injury, which you can't say about every herb, though very high amounts of silibinin, its main compound, have raised bilirubin and liver enzymes. Product quality is the bigger worry: some supplements hold quite different amounts of silymarin than the label says, and others have been found contaminated, so check for testing.
What it interacts with
- Diabetes medicinesIt may lower blood sugar further, so tell your doctor before you start.
- WarfarinMilk thistle weakly slows a liver pathway that clears warfarin, and one person's INR, their clotting number, rose from 2.64 to 4.12 on a liver cleanse containing it, then settled after stopping. Ask first, and expect closer checks.
- Losartan, a blood pressure medicineThis has been tested. After 2 weeks of silymarin, healthy men made less of losartan's active form, and in those with the most common gene type, more losartan stayed in the blood. Tell your doctor.
- Phenytoin, a seizure medicineIt uses that same liver pathway, and small changes matter with it. Ask first.
- Haloperidol, risperidone and aripiprazoleSeven cases of an inflamed pancreas were reported with milk thistle alongside haloperidol or risperidone, and one liver problem with aripiprazole. Talk to your doctor before combining them.
- Sirolimus, a transplant medicineIn kidney transplant patients with liver problems, silymarin was linked to slower clearing of this medicine. Tell your transplant team.
- Raloxifene, a bone and breast medicineIn lab tests, milk thistle compounds blocked how the gut breaks it down, and models predict higher levels. It hasn't been measured in people. Ask first.
- Talinolol, a heart medicineLevels rose by about a third after 2 weeks of silymarin in healthy men.
- RosuvastatinA small study found no change in this statin, which is reassuring.
- Other medicinesMany human studies found no big interactions, but not all. A pharmacist can check your exact list.
Goes well with
Side effects
- Usually well tolerated. The most common effects are bloating, nausea and gas.
- Allergic reactions, mostly in people allergic to its plant relatives. Itching, rash and hives have also been reported.
Check first if
- Ragweed, chrysanthemum, marigold or daisy allergies: it's a relative and may set off a reaction.
- Pregnancy or breastfeeding: little is known, so check with your doctor. Its effect on breast milk is unclear.
- Diabetes: watch your sugar and talk to your doctor.
- Hormone-sensitive conditions: lab work shows its compounds have mild estrogen-like effects, so ask first.
- Kidney transplant, or planning one: talk to your transplant team.
- Liver disease: see your doctor. This is no replacement for care, and your levels may run higher.
The blood tests that go with it
- ALTThe liver number studies watched most. Some saw it fall.
- ASTRead with ALT for a fuller picture of your liver.
- GGTAnother liver enzyme, which fell in one small study.
- Fasting glucoseFell in small studies of people with type 2 diabetes.
- HbA1cYour blood sugar over about three months, also lower in those studies.
- TriglyceridesFell in people with fatty liver.
- INRYour clotting number, if you take warfarin.
- BilirubinAnother liver number, which very high amounts of milk thistle's main compound have raised.
Work it out
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These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease.
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Questions
What is milk thistle good for?
Mostly the liver, by long tradition. Blood sugar is the other area people look at. The research on both is limited, so it's a reasonable thing to try and check, not a proven fix.
How long does milk thistle take to work?
You won't feel it. Liver studies ran from 4 weeks to nearly a year, so a blood test after a few months is the honest way to tell.
What are the side effects of milk thistle?
Mostly mild gut effects: bloating, nausea and gas. Some people get allergic reactions, especially if they react to ragweed or daisies.
What does milk thistle interact with?
Diabetes medicines are the main one, because of blood sugar. It can also slow how your liver clears drugs like warfarin, losartan and phenytoin, and there are reports with some antipsychotic medicines and sirolimus.
Does milk thistle clean your liver?
There's no good evidence it cleans anything. Your liver does that job on its own. Milk thistle may nudge some liver numbers, but studies disagree.
Who should not take milk thistle?
Anyone allergic to ragweed, daisies or marigolds. If you're pregnant, breastfeeding, have diabetes, a hormone-sensitive condition or a kidney transplant, or take warfarin, ask your doctor first.
Can I take milk thistle every day?
Studies gave it daily for up to 48 weeks without serious problems linked to it. If you plan to stay on it, check your liver numbers now and then.
What's the half-life of milk thistle?
Silymarin's compounds halve in 1 to 3 hours, and the forms your liver makes from them in 3 to 8. Most is gone within a day.
Does milk thistle help with fatty liver?
It's unclear. Some studies found lower liver numbers and others didn't, and the largest review called the evidence very uncertain. Weight and diet changes have far stronger support, so talk to your doctor.
Does milk thistle increase breast milk?
People have used it that way for a long time, but its effect isn't clear, and little is known about its safety while breastfeeding.
Sources
- NIH National Center for Complementary and Integrative Health. Milk thistle.
- LiverTox, NIH. Milk thistle.
- Wang C et al. Silymarin for adults with metabolic dysfunction-associated steatotic liver disease. Cochrane Database Syst Rev, 2025.
- Malik A et al. Effects of silymarin use on liver enzymes and metabolic factors in steatotic liver disease. Can Liver J, 2024.
- Voroneanu L et al. Silymarin in type 2 diabetes mellitus. J Diabetes Res, 2016.
- Wen Z et al. Pharmacokinetics and metabolic profile of silymarin flavonolignans in human plasma. Drug Metab Dispos, 2008.
- Schrieber SJ et al. The pharmacokinetics of silymarin is altered in patients with hepatitis C virus and nonalcoholic fatty liver disease. Drug Metab Dispos, 2008.
- Tvrdý V et al. Systematic review of pharmacokinetics and potential interactions of flavonolignans from silymarin. Med Res Rev, 2021.
- Hermann R, von Richter O. Clinical evidence of herbal drugs as perpetrators of pharmacokinetic drug interactions. Planta Med, 2012.
- Han Y et al. Effect of continuous silymarin administration on oral talinolol in healthy volunteers. Xenobiotica, 2009.
- Deng JW et al. Effect of silymarin supplement on the pharmacokinetics of rosuvastatin. Pharm Res, 2008.
- Thu OK et al. Effect of commercial Rhodiola rosea on drug-clearing enzymes in humans. Eur J Clin Pharmacol, 2016.
- Han Y et al. Effect of silymarin on losartan and its active form in healthy Chinese volunteers. Eur J Clin Pharmacol, 2009.
- Woroń J, Siwek M. Unwanted effects of psychotropic drug interactions with plant extracts. Psychiatr Pol, 2018.
- Jiao Z et al. Population pharmacokinetics of sirolimus in Chinese adult renal transplant patients. Br J Clin Pharmacol, 2009.
- Gufford BT et al. Milk thistle constituents inhibit raloxifene intestinal glucuronidation. Drug Metab Dispos, 2015.
- Memorial Sloan Kettering Cancer Center. Milk thistle.
Written by LifeFrom from these sources, and not yet reviewed by a clinician. Talk to your doctor before starting a supplement.
