Compound Monograph
Silydianin
Silydianin is the fourth and one of the more minor flavonolignans of milk thistle's silymarin complex (~5–10% of it), and structurally the odd one out — it has an unusual bicyclic skeleton rather than the benzodioxane linkage of its siblings. It is a moderate antioxidant (stronger than silybin, weaker than silychristin in vitro). Evidence is thin and preclinical or class-level, with no isolated-silydianin human trials.
Sources · 1
Where Does It Come From?
Silydianin is a naturally occurring flavonolignan, found in Milk Thistle. It is well tolerated orally (low toxicity).
Concentration
Content by Source
Concentrations not reported. No percent-dry-weight or mg/g figures have been published for this compound in its source plants.
Silydianin at a Glance
Silydianin is the fourth and one of the more minor flavonolignans of milk thistle’s silymarin complex, making up around 5–10% of it.
Structurally it is the odd one out: it has an unusual bicyclic skeleton rather than the benzodioxane linkage shared by silybin, isosilybin and silychristin — which means “silymarin” is not a family of near-identical molecules but a mixture containing at least one structurally distinct member.
What It's Used For
Silydianin is the fourth flavonolignan of the silymarin complex from milk thistle seed — a minor sibling (~5–10%) of the dominant silybin (silibinin), isosilybin and silychristin. Its distinctive feature is structural, not pharmacological: unlike the others it has an unusual bicyclic skeleton (a keto group adjacent to a hemiacetal) rather than the typical benzodioxane-type linkage — the “odd one out” of the group. Its own literature is genuinely scant, and as with the other congeners, milk thistle’s clinical evidence rests on the silymarin complex/silibinin, not isolated silydianin.
Support is an experimental score — weighted by study type (human > animal > in vitro) and volume. A beta, not a validated metric. Genuinely thin isolate literature, so scores stay low by design.
In DPPH ranking, the order was silymarin > silychristin > silydianin > silybin — so silydianin is an intermediate scavenger, stronger than silybin but weaker than silychristin 2Reference 2Silymarin and its components scavenge phenylglyoxylic ketyl radicalsView study →, and a review places the non-silybin congeners (silydianin included) as potentially better antioxidants than the headline silybin 1Reference 1Looking beyond silybin: the importance of other silymarin flavonolignansView study →. (Note: the common assumption that silydianin is the weakest of the group does not hold — silybin usually is.)
Gap: in-vitro chemistry only, with no cellular-outcome or human antioxidant-endpoint data for the isolate 2Reference 2Silymarin and its components scavenge phenylglyoxylic ketyl radicalsView study →.
Silydianin contributes to the silymarin complex’s cytoprotection — for example against anthracycline toxicity in cardiomyocytes 6Reference 6AnimalChemoprotective effect of plant phenolics against anthracycline-induced toxicity on rat cardiomyocytes: silymarin and its flavonolignansView study → and in the skin-protective (UV/oxidative) activity of the flavonolignan set 5Reference 5Skin-protective activity of silymarin and its flavonolignansView study →.
Gap: the actual hepatoprotective clinical evidence belongs to silymarin/silibinin and must not be transferred to this isolate 1Reference 1Looking beyond silybin: the importance of other silymarin flavonolignansView study →.
Silymarin enhanced alkaline phosphatase and osteocalcin in osteoblasts and improved fracture healing in mice 3Reference 3AnimalOsteogenic activity of silymarin through enhancement of alkaline phosphatase and osteocalcin in osteoblasts and tibia-fractured miceView study →, and the congener silibinin promotes osteoblastogenesis while suppressing osteoclast differentiation 4Reference 4Osteoblastogenesis and osteoprotection enhanced by the flavonolignan silibinin in osteoblasts and osteoclastsView study →.
Gap: this is complex-/silibinin-level, with no silydianin-specific bone study — honest class context only 3,
Mechanisms
| Target / pathway | Effect | Relevant to |
|---|---|---|
| Free radicals (DPPH, ketyl) | direct scavenging, moderate (> silybin, < silychristin) | antioxidant |
| Nrf2 / antioxidant-response (class-level) | proposed cytoprotective-gene induction (inferred, not isolate-proven) | antioxidantcytoprotective |
| Osteoblast markers (ALP, osteocalcin; class-level) | enhanced for silymarin/silibinin, not silydianin specifically | bone (exploratory) |
Pharmacokinetics
Silydianin shares the flavonolignan class’s poor aqueous solubility and poor oral bioavailability — the seed complex is not water-soluble, so teas do not deliver a meaningful dose, and standardized extracts or phospholipid complexes are used for the parent complex 1Reference 1Looking beyond silybin: the importance of other silymarin flavonolignansView study →. No dedicated human pharmacokinetic study of the isolate exists, so low systemic exposure from oral intake should be assumed, and silydianin’s distinctive reactive bicyclic structure also makes it comparatively chemically labile.
Clinical trials
There are no trials of isolated silydianin. All human evidence tied to milk thistle is on the silymarin complex or silibinin/silybin (NAFLD, chronic liver disease, IV Legalon SIL for Amanita poisoning) — not this single molecule.
| Completed | Planned | Terminated | Preclinical |
|---|---|---|---|
| —(none, isolate) | — | — | Minimal(comparative chemistry; class-level) |
Last checked: July 2026.
Toxicity & Safety
Silydianin has no toxicity signal of its own, and reaches people only as a minor fraction of a well-tolerated milk-thistle extract. The one real caution belongs to the source herb — Asteraceae allergy — rather than to the molecule.
- No signal of intrinsic toxicity. It reaches humans normally only as ~5–10% of a well-tolerated seed extract.
- No distinctive target-based caveat. Unlike its sibling silychristin, no MCT8 activity is reported.
- Avoid the isolate in pregnancy and lactation.
- Asteraceae allergy. This caution applies to milk-thistle products generally — a source-herb issue, not a molecular one.
Full Safety & Interactions Detail
Silydianin has a low toxicity verdict — no signal of intrinsic toxicity, and it reaches humans normally only as a minor (~5–10%) fraction of a well-tolerated seed extract. Unlike its sibling silychristin it carries no distinctive target-based caveat (no MCT8 activity reported), and Asteraceae-allergy caution applies to milk-thistle products generally.
Dosage
There is no established therapeutic dose — silydianin is not sold or dosed as an isolate and is consumed only as ~5–10% of a standardized silymarin extract, so any figure would be extrapolation from the complex.
References
- Selc M, Babelova A (2025). Looking beyond silybin: the importance of other silymarin flavonolignans. Frontiers in Pharmacology. https://pubmed.ncbi.nlm.nih.gov/40761399/
- Sersen F, et al. (2006). Silymarin and its components scavenge phenylglyoxylic ketyl radicals. Fitoterapia. https://pubmed.ncbi.nlm.nih.gov/16956731/
- Kim JL, et al. (2012). Osteogenic activity of silymarin through enhancement of alkaline phosphatase and osteocalcin in osteoblasts and tibia-fractured mice. Experimental Biology and Medicine. https://pubmed.ncbi.nlm.nih.gov/22496431/
- Kim JL, et al. (2012). Osteoblastogenesis and osteoprotection enhanced by the flavonolignan silibinin in osteoblasts and osteoclasts. Journal of Cellular Biochemistry. https://pubmed.ncbi.nlm.nih.gov/21898547/
- Vostálová J, et al. (2019). Skin-protective activity of silymarin and its flavonolignans. Molecules. https://pubmed.ncbi.nlm.nih.gov/30875758/
- Chlopčíková Š, et al. (2004). Chemoprotective effect of plant phenolics against anthracycline-induced toxicity on rat cardiomyocytes: silymarin and its flavonolignans. Phytotherapy Research. https://pubmed.ncbi.nlm.nih.gov/15022159/
