Milk Thistle Dosage: How Much Silymarin (~420 mg/day)
Educational summary — not medical advice. See does it work for the ragweed-family allergy and antidiabetic-drug cautions.
The honest answer
The studied dose is 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.
The key thing most people get wrong: the dose is silymarin
Milk thistle's benefit comes from silymarin, a complex of flavonolignans (main component: silibinin). So the research doses 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 |
|---|---|
| How much? | ~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 what % of the ~420 mg common target you're getting.
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.
How to take it
- Target ~420 mg silymarin/day (about 200 mg 2–3×), within the ~140–800 mg studied range — splitting the dose across the day is how the trials gave it.
- 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.
- Take with food to ease the mild GI upset that's the most common side effect, and to aid absorption of the poorly-soluble silymarin.
- Set expectations honestly. The evidence is modest — a reduction in elevated ALT/AST as an adjunct, not a liver "detox" or cure; see does it work.
The verifiable-dose pick
The most useful product for hitting a known dose is one that prints a silymarin % so you can compute the active. The cheapest 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. About 1.8 servings reaches the ~420 mg target — and because the % is printed, you can actually verify it.
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Frequently asked questions
How much milk thistle should I take per day?
Measured 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. For hitting a known dose, prioritize 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
- Does milk thistle work? — the honest evidence, 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).