Isosilybin

PhytochemicalFlavonolignanBest with a meal

What is it

Isosilybin is one of the flavonolignans that make up silymarin, the active complex extracted from milk thistle (Silybum marianum). It exists as isosilybin A and B, alongside silybin A/B, silychristin, and silydianin.

Evidence for 1 use

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Liver support (silymarin complex)

Limited Evidence

Standardized silymarin shows modest benefit in some liver conditions (NAFLD, alcohol- and drug-induced injury). Specific contribution of isosilybin is not well characterized.

How it works

Isosilybin and related milk thistle flavonolignans scavenge free radicals, stabilize hepatocyte membranes, and modulate inflammatory and fibrotic signaling in liver cells. They also inhibit certain CYP enzymes and may affect tumor cell signaling in vitro. Specific in vivo evidence for isolated isosilybin is limited; most clinical research is on standardized silymarin extracts.

Dosage

No RDA. Standardized silymarin extracts typically supply 140-420 mg/day total flavonolignans; isolated isosilybin is rarely dosed separately. DSLD does not report a median.

When and how to take it

No strict timing requirement. Often taken with meals to support absorption.

2 commercial forms

Compare the main delivery options and what they’re best suited for.

Part of silymarin complex

How isosilybin is typically consumed.

Low oral bioavailability of free flavonolignans.

Phytosome (silybin-phosphatidylcholine)

Targets silybin; isosilybin content varies by extract.

Significantly improves absorption.

Safety

Milk thistle and its constituents are generally well tolerated; mild GI symptoms and rare allergic reactions are reported.

Who should be cautious

People with allergies to the Asteraceae family (ragweed, daisy) may react. Use under guidance if on multiple prescription medications metabolized by CYP enzymes.

Interactions

Silymarin components may inhibit CYP2C9 and CYP3A4 in vitro, but clinically significant interactions are uncommon. Theoretical interaction with warfarin, statins, and some chemotherapy.

Frequently asked questions

Is isosilybin the same as silybin?⌄

They are closely related flavonolignans in milk thistle but are distinct molecules with slightly different activities.

Should I buy an isosilybin supplement?⌄

Standardized milk thistle (silymarin) extracts are the practical option; isolated isosilybin is rare and not well studied alone.

References

Isosilybin on Wikidata — Wikidata link

Isosilybin (ChEBI:80744) — ChEBI link

Isosilybin (PubChem CID 21723007) — PubChem link

Isosilybin on NIH DSLD (US supplement label database) — NIH Dietary Supplement Label Database link

Research on Isosilybin (PubMed search) — PubMed link

Track Isosilybin with Pilora

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Evidence-based·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.