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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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 $0.10 to $1.28 a day across 11 brands — a 13× gap. 3 of the 12 state some certification on the listing itself, which is a different and weaker claim than appearing in the registry above: one is what the Milk Thistle (Silymarin) label says, the other is what a certifier confirms.
Method: the 12 Milk Thistle (Silymarin) products in our catalogue, each priced at its own labelled serving rather than by pack size, across 11 brands. How we price.
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).