How much milk thistle should you take a day?

There's no official recommended daily amount for milk thistle — no RDA, no established upper limit. What exists instead is a range of doses used in human research and a wide range of doses sold on labels, and the two often don't match. The dose that shows up again and again across independent human trials is 420 mg of silymarin a day, split into three 140 mg doses.

What the trials actually used

Three separate human studies — a pharmacokinetic interaction trial, a cytochrome P450 screening study, and a randomized trial in people with a diagnosed kidney condition — each dosed a standardized milk thistle extract at 140 mg three times a day, for a 420 mg/day total of silymarin. That consistency across independently run trials is why 420 mg/day shows up as the reference point in most discussions of milk thistle dosing, even though no single body has adopted it as an official recommendation. A 2019 safety review found silymarin well tolerated even at much higher doses — up to 700 mg three times a day (2,100 mg/day) for 24 weeks in the trials it covered — with gastrointestinal effects like nausea and diarrhea as the main limiting factor as the dose rises. See milk thistle side effects for more on that.

Why the label number and the research number often don't match

Commercial labels range enormously — searches turn up products listing 150 mg, 250 mg, 500 mg, 1,000 mg and higher of "milk thistle extract," sometimes with a stated silymarin percentage and sometimes without one. A "1,000 mg milk thistle" capsule could contain far more or far less silymarin than a "500 mg" capsule from a different brand, depending on how concentrated the extract is. The 420 mg/day figure above refers specifically to silymarin, the standardized active complex — not to raw milk thistle seed weight or an unstandardized extract's total milligrams. How to choose a good milk thistle supplement covers how to read a label for that distinction.

Splitting the dose

Every trial referenced above split the daily total into three doses rather than giving it all at once. When is the best time to take milk thistle covers what's known — and what isn't — about timing and absorption.

When the number is different for you

• Liver or kidney disease: talk to your doctor before adding any dose of milk thistle if you have a diagnosed liver or kidney condition, since the dosing research above was conducted in people already diagnosed and monitored by a doctor, not as a general self-directed dose.
• Pregnancy or breastfeeding: ask your doctor before taking milk thistle at any dose if you're pregnant or nursing, since the safety data in that situation is limited.
• Other medications: some research has found milk thistle affects how the body processes certain drugs, so check milk thistle and medications: what to check before combining any dose with a prescription.
• Pets: this guide covers human dosing only, so ask a veterinarian for a dose specific to your dog, cat or other animal rather than scaling down a human number.

Questions people ask

How much milk thistle should I take a day?

There's no official recommended amount. The dose that recurs across independent human trials is 420 mg of silymarin a day, taken as three 140 mg doses — but that's what's been studied, not a universal recommendation, and it was studied in people with a diagnosed condition, not as a general-population dose.

Is 1,000 mg of milk thistle too much?

It depends entirely on how much silymarin that 1,000 mg actually contains, which the label may or may not state. A 2019 safety review found doses as high as 2,100 mg/day of silymarin (700 mg three times daily) well tolerated for 24 weeks in the trials it covered, with gastrointestinal symptoms as the main limiting effect — but that's silymarin specifically, not unstandardized extract or raw seed weight.

How much milk thistle per day for the liver?

The trials that tested liver-related outcomes most often used 420 mg/day of silymarin, split into three doses — but those trials were run in people with a diagnosed liver condition under medical supervision, and results were mixed. See milk thistle benefits: what the research does and doesn't show for what those trials actually found.

What's the dose for dogs?

This guide only covers doses used in human research. Ask a veterinarian for guidance specific to your pet rather than scaling down a human dose.

Related reading: what is milk thistle, how to choose a good milk thistle supplement, and when is the best time to take milk thistle.