Milk Thistle Dosage: Silymarin Amounts Studied and Label Math
The honest answer
Studied amounts are measured in silymarin, not seed weight: about 200 mg silymarin 2–3×/day (~420 mg/day), within a range of ~140–800 mg/day. Compute the actual active with extract mg × silymarin % (standardized extracts are ~70–80%). The critical caveat: you often can't compute it, because most labels don't disclose the silymarin % — only 5 of 12 products we track do.
Educational summary — not medical advice. See what the research says for the ragweed-family allergy and antidiabetic-drug cautions.
The key thing most people get wrong: the dose is silymarin
Milk thistle's main active extract is silymarin, a complex of flavonolignans (main component: silibinin). So research measures amounts in silymarin milligrams, not seed grams — commonly ~200 mg silymarin 2–3 times a day (roughly 420 mg/day), across a studied range of about 140–800 mg/day. Because the pharmacopeial standard (USP / German Commission E) is an extract standardized to about 70–80% silymarin, you convert the label number to active with a single multiplication: silymarin mg = extract mg × silymarin %. A 300 mg extract at 80% is ~240 mg silymarin; a 150 mg extract at 80% is ~120 mg. But if the label prints only "1,000 mg," "4:1," or "full-spectrum" with no percentage, the multiplication has no second number — and the dose is unknowable.
| Question | Answer |
|---|---|
| Amount studied | ~200 mg silymarin 2–3×/day (~420 mg/day); studied range ~140–800 mg/day |
| Measured in what? | Silymarin, not seed/extract weight |
| Convert extract to active | silymarin mg = extract mg × silymarin % (standardized ~70–80%) |
| Example | 300 mg extract × 80% = ~240 mg silymarin/serving |
| Can I compute it from the label? | Only if a silymarin % is printed — most labels don't disclose it |
Silymarin calculator: how much active are you actually getting?
This only works if your product discloses a silymarin % — most don't, which is the whole point. If you have the extract mg per serving and a disclosed silymarin %, enter them with your servings per day to see your actual daily silymarin in mg and how that compares with the ~420 mg amount commonly studied.
Where to find the number: look for an extract "standardized to X% silymarin" next to the milk-thistle mg on the Supplement Facts panel (then silymarin mg = extract mg × X%). If the label only says "milk thistle 1,000 mg," "3,000 mg 4:1," or "full-spectrum," the silymarin is undisclosed — you can't use this, and that's the finding.
About the label math
- Research has used ~420 mg silymarin/day (about 200 mg 2–3×), within a ~140–800 mg range, with the dose split across the day. That describes the studies, not advice for you; ask a clinician.
- Compute from the %, not the big number. A "150 mg standardized to 80%" (= 120 mg silymarin) is more useful than an undisclosed "3,000 mg" — see the label trap.
- Many people take it with food to ease mild GI upset, the most common side effect.
- Set expectations honestly. The evidence is modest and mixed; nothing here shows milk thistle treats a liver condition or that it is a liver "detox"; see what the research says.
A product that prints its silymarin %
A product that prints a silymarin % lets you compute the active amount. The lowest-cost such product per 100 mg of silymarin is below; full ranking on best milk thistle.
Standardized to 80% — 300 mg extract × 80% = ~240 mg silymarin/serving. Because the % is printed, you can compute the silymarin per serving yourself.
Ranked by disclosed silymarin, never commissions.
Price check · Milk Thistle (Silymarin)
What Milk Thistle (Silymarin) actually costs across the brands we track
What you pay. The 12 Milk Thistle (Silymarin) products here run $0.08 to $1.28 a day across 11 brands, a 16× gap. Some of these state a certification on the listing itself. That is a weaker claim than a certifier confirming it: a listing repeats what the brand says, and a registry entry shows what a certifier has checked.
Method: the 12 Milk Thistle (Silymarin) products in our catalogue, each priced at its own labeled serving rather than by pack size, across 11 brands. How we price.
Frequently asked questions
What amounts of milk thistle have been studied?
Research measured it in silymarin: ~200 mg 2–3×/day (~420 mg/day), range ~140–800 mg. Compute active as extract mg × silymarin % (standardized ~70–80%). If no % is printed, you can't compute it.
How do I convert extract mg to silymarin?
Multiply by the disclosed %. A 150 mg extract at 80% is ~120 mg silymarin; a 300 mg extract at 80% is ~240 mg. No percentage means the dose is unknown.
Why can't I tell how much silymarin is in my supplement?
Because most labels print extract weight, a 4:1 ratio, or "full-spectrum" — not silymarin. Testing found ~2,800% variation (independent) and 35–125% of label (peer-reviewed). Only 5 of 12 products we track disclose a %.
Standardized extract or phospholipid form?
A standardized extract with a disclosed % is the most verifiable (you can compute the active). A phospholipid form (Siliphos) is built for absorption but isn't raw-mg comparable. If you want a known amount, look for a printed %.
Related
- The silymarin label trap — why the big milligram number isn't the dose
- Best milk thistle — ranked by disclosure, then cost per 100 mg silymarin
- What the research says about milk thistle, including the mortality null
Sources
- U.S. Pharmacopeia / German Commission E monographs — milk thistle extract standardized to ~70–80% silymarin; commonly dosed ~200 mg silymarin 2–3×/day. Pharmacopeial convention, not a single clinical trial.
- Fenclová M, et al. "Poor chemical and microbiological quality of commercial milk thistle supplements." Sci Rep. 2019. PMID: 31366891 (silymarin content 35–125% of declared).
- ConsumerLab.com. Milk thistle supplements review (independent testing; silymarin per serving varied ~2,800%). Not peer-reviewed; full results member-only.
- Full product dataset: /milk-thistle/cost-by-brand.json (CC BY 4.0).