01 — Evidence
Evidence Summary
The clearest thing to say about fisetin in humans is what is still missing: no completed trial has shown an effect on tumor response, progression or survival. But the human tier is not empty — one small randomised trial in colorectal-cancer patients measured inflammatory biomarkers during chemotherapy, there is genuine human pharmacokinetic data, and supportive-care trials are ongoing. The broad case for tumor-directed activity sits underneath, entirely in cell and animal studies, at exposures far above what an oral dose reaches in a person.
Human
Clinical Record
A biomarker trial + PK + supportive care
No completed trial has shown an effect on a tumor — but the human tier is not empty. A small colorectal-cancer trial measured inflammatory biomarkers during chemotherapy.
- In colorectal-cancer patients on chemotherapy, fisetin significantly lowered one inflammatory biomarker (IL-8) versus placebo — but tumor response and survival were not assessed
- A randomised crossover showed an enhanced formulation raised systemic exposure many-fold, with only minor gastrointestinal effects
- Supportive-care survivorship trials (physical function, frailty, fatigue) are ongoing, without results
Animal
Preclinical Signal
Xenograft + carcinogenesis models
Fisetin reduced tumor burden across several cancer types in animals — but generally by injection or high oral doses, and often as a chemo-combination or prevention rather than shrinking an established tumor.
- Oral fisetin inhibited a head-and-neck tumor and modulated apoptosis in a lung-carcinogenesis model
- Systemic fisetin reduced tumor growth and lung metastases in a triple-negative breast-cancer model
- Pancreatic tumors were suppressed across several signaling pathways, in multiple independent studies
In Vitro
Cell Model Data
Broad mechanism panel; concentration-dependent
Fisetin's deepest layer is broad, multi-pathway anticancer activity across many cell lines — reproduced across laboratories, but at concentrations far above what an oral dose reaches in blood.
- Triggered tumor-cell death through the mitochondrial (Bax/Bcl-2) apoptosis route
- Suppressed the PI3K/AKT/mTOR, MAPK, Wnt and NF-κB growth-signaling pathways
- Reversed the invasion and stem-cell programmes that let cancer cells spread
Human
Clinical Record
No completed interventional trial has reported whether fisetin affects tumor response, progression, or survival. The cancer-trial footprint is mostly supportive and survivorship research — randomised trials of fisetin to improve physical function, prevent frailty, or reduce fatigue in cancer survivors — plus one early-phase treatment trial testing senolytic drug combinations that include fisetin in previously treated glioma. All are recruiting or ongoing and none has reported results, and none tests fisetin as a single anticancer agent.[26] One completed randomised trial in colorectal-cancer patients did measure inflammatory biomarkers during chemotherapy (below), but the human anticancer-efficacy question remains open.
Continue reading — full research detail+
The first — and so far only — human pharmacokinetic study was a randomised, double-blind crossover in 15 healthy volunteers. It compared 1,000 mg of unformulated fisetin against a fenugreek-galactomannan hydrogel formulation (Hybrid-FENUMAT™, "FF-20") delivering 192 mg of fisetin. The formulation produced roughly 26.9-fold higher AUC and 23.9-fold higher peak plasma concentration (238 ng/mL versus about 10 ng/mL), kept free fisetin measurable in plasma out to 8 hours rather than 2, and lowered the ratio of the metabolite geraldol to parent fisetin (though absolute geraldol exposure rose too) — with no significant adverse events, only two minor gastrointestinal complaints across both arms.[1] This establishes that meaningfully higher systemic exposure is achievable in people, but it says nothing about an anticancer effect. It is also the only published human fisetin PK comparison identified: it was funded by the formulation's developer, whose staff and the commercial seller's staff co-authored it, and no independent replication has been identified.
The one completed trial in an oncology population is a biomarker study, not an efficacy study. A randomised, double-blind trial gave 37 colorectal-cancer patients undergoing chemotherapy either fisetin 100 mg/day or placebo for seven weeks, starting one week before chemotherapy. Compared with placebo, the fisetin group showed a significant reduction in one inflammatory biomarker, interleukin-8; changes in hs-CRP, MMP-7, MMP-9 and IL-10 were not significantly different between groups (some fell within the fisetin group but not relative to placebo). Crucially, the trial did not assess tumor response, progression or survival.[31] So this is genuine repeated-dose human oncology exposure with a modest inflammatory signal — not evidence that fisetin controls cancer.
Most oncology trials are supportive-care and survivorship studies, testing whether fisetin's preclinical senolytic activity can reduce therapy-associated senescent-cell burden or its downstream effects (physical function, frailty, fatigue) — not tumor killing: randomised trials of fisetin, alone or with exercise, in breast-cancer and childhood-cancer survivors. Separately, one early-phase treatment trial in previously treated glioma tests drug combinations (dasatinib, quercetin, fisetin and temozolomide) — a treatment study rather than supportive care, though its multi-drug design would not isolate fisetin's contribution. All are recruiting or ongoing, and none has reported an outcome.[26]
Signal maturity: the human record is early-stage — a small colorectal-cancer biomarker trial, controlled single-dose pharmacokinetics, and a growing set of registered supportive-care and one early-phase treatment trial. What is still missing is the important part: no completed study has shown that fisetin changes tumor response, progression or survival. Human anticancer-efficacy evidence is, at present, absent — but human oncology exposure is not.
Animal
Preclinical Signal
Across several cancer types, fisetin reduced tumor burden in animals — but the doses are weight-adjusted, frequently given by injection or at high oral levels, and several of the strongest effects are chemo-combinations or prevention rather than regression of an established tumor.[3,4,5]
Continue reading — full research detail+
In a genetic Apc/Pik3ca mouse model of intestinal tumorigenesis, fisetin alone (1 mg/animal intraperitoneally) reduced tumor incidence to 40% versus 71% in controls, and combined with 5-fluorouracil reduced tumor multiplicity (4±2 versus 12±4 tumors) — without causing established tumors to regress, so this is a prevention signal.[3] Oral fisetin (50 mg/kg for 19 days) inhibited a head-and-neck xenograft by roughly 73% with reduced Ki-67 and increased cleaved caspase-3,[4] and oral fisetin (25 mg/kg) modulated the mitochondrial apoptosis axis in a benzo(a)pyrene lung-carcinogenesis model.[13]
Systemic fisetin (100 mg/kg intraperitoneally) reduced tumor growth and the number of lung metastatic nodules in a triple-negative breast-cancer xenograft.[5] Pancreatic xenografts were suppressed in several independent studies — through fisetin-induced DNA damage,[27] PI3K/AKT/mTOR inhibition,[28] Wnt/β-catenin suppression,[29] and cancer-stem-cell depletion that also enhanced gemcitabine.[30] The recurring caveat is the route and dose: these are injected or high oral animal exposures, and several depend on pairing fisetin with a chemotherapy drug.
Signal maturity: tumor-growth suppression is real and reproduced across colorectal, head-and-neck, breast and pancreatic models, including by oral dosing in one head-and-neck study — but it is achieved at exposures a human oral dose is unlikely to reach, and the colorectal result is prevention rather than regression.
In Vitro
Cell Model Data
Fisetin's deepest layer is broad, multi-pathway anticancer activity reproduced across colorectal, head-and-neck, breast, prostate, lung, melanoma, pancreatic, epidermoid and leukaemia cell lines — suppressing the PI3K/AKT/mTOR, MAPK, Wnt and NF-κB pathways while driving apoptosis and cell-cycle arrest.[25]
Continue reading — full research detail+
The recurring molecular signature is a Bax/Bcl-2 shift with cytochrome c release, caspase activation and PARP cleavage, cell-cycle arrest at G1/S or G2/M, and reversal of epithelial–mesenchymal-transition markers — reported repeatedly and across independent laboratories.[25] A notable nuance appears in colorectal cells, where fisetin lowered the antioxidant regulator Nrf2 and raised reactive oxygen species to drive apoptosis[6] — the reverse of its Nrf2-raising, ferroptosis-protective behavior in normal tissue, and the clearest sign that its redox effect is context-dependent.
The load-bearing caveat runs through all of it. Effective in-vitro concentrations cluster in the 10–120 µM range, whereas the highest unconjugated (parent) plasma fisetin measured in humans is about 0.8 µM even with an enhanced formulation (and roughly 0.03 µM unformulated) — one to three orders of magnitude lower.[1] This is strong evidence of a translational exposure problem, and a real reason not to assume laboratory findings translate to oral human use. It is not proof that no biological activity can occur: the human study measured only parent fisetin and its active metabolite geraldol, not the circulating conjugates or the actual concentration reached inside a tumor, so the gap limits translation rather than closing the question.
Signal maturity: the growth-signaling-suppression and apoptosis mechanisms are the deepest, most consistently replicated findings for this compound, spanning many cancer types across many publications. Their ceiling is exposure: the concentrations that produce them sit far above what oral fisetin achieves in human plasma.
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02 — Pathways
Pathway Interaction Profile
Fisetin engages several distinct biological pathways relevant to tumor behavior, grouped below by the functional role each one supports. These are direct anti-tumor mechanisms from cell and animal research, and — further down — a separate, preclinical set of pathways where fisetin protected a healthy organ from a chemotherapy drug. Every mechanism below carries the same caveat: it was demonstrated at exposures an oral human dose is unlikely to reach.
Fisetin's Contain classification rests on reported suppression of the metastatic and tumor-niche programme — inflammatory signaling, blood-vessel growth, invasion and epithelial–mesenchymal transition, and cancer stem-cell markers — across several cancer types, with one live-animal reduction in lung metastases. It is partial because the evidence is cell and injected-animal work at exposures an oral human dose is unlikely to reach.
Block Seeding & Niche Formation
Research concerning formation of supportive pre-metastatic niches at distant sites.
NF-κB / TNF-α / IL-6 inflammatory axis
In human colon cancer cells, fisetin has been reported to inhibit NF-κB activation and EGFR signaling while inducing apoptosis and suppressing anchorage-independent colony growth.[2] A separate liver-cancer study adds an in-vivo, immunocompetent line of support with a different inflammatory mechanism: fisetin inhibited neutrophil extracellular trap formation via AKT/ROS, weakened NET-driven proliferation and invasion, and reduced tumor growth, neutrophil recruitment and intratumoral NETs in mice.[35] Fisetin's broader anti-inflammatory NF-κB activity is best documented outside cancer models, so the tumor-niche claim is kept to what these studies show.
COX-2 / PGE₂
In human colon cancer cells (HT29), fisetin has been reported to downregulate COX-2 protein specifically — leaving COX-1 unaffected — and to inhibit secretion of the pro-inflammatory lipid PGE₂, alongside reduced β-catenin/TCF-4 signaling.[2] A single in-vitro colorectal study underlies this node.
Angiogenesis / VEGF / HIF-1α
In hypoxic lung carcinoma cells, fisetin has been reported to suppress hypoxia-induced VEGF at low micromolar concentrations by a HIF-1α–independent mechanism — notably, it raised HIF-1α (which entered the nucleus but formed a transcriptionally inactive complex) while suppressing STAT3 signaling, the effect that tracked its VEGF-inhibitory potency.[10] Its active metabolite geraldol separately accumulated in tumors and inhibited endothelial-cell migration.[11] Fisetin does not lower HIF-1α — a common misstatement.
Prevent Tumor Cell Shedding
Research concerning invasion and escape from existing lesions (EMT and ECM breach).
EMT & metastatic invasion
Fisetin has been reported to reverse epithelial–mesenchymal transition and reduce invasion across three cancer types. In triple-negative breast cancer it raised E-cadherin and lowered N-cadherin, vimentin and Snail through PTEN/Akt/GSK-3β signaling, and — the strongest single finding — reduced tumor growth and the number of lung metastatic nodules in a live xenograft.[5] In non-small-cell lung cancer it raised E-cadherin and lowered vimentin, N-cadherin and MMP-2 while suppressing β-catenin, NF-κB, EGFR and STAT3.[8] In prostate cancer it inhibited the oncoprotein YB-1, reducing EMT markers in cells and in a xenograft.[9]
Prevent Dormant Reactivation
Research concerning wake-up signalling and reactivation of dormant disseminated tumour cells.
Cancer stemness (CD44, ALDH, Nanog/Sox2)
In non-small-cell lung carcinoma cells, fisetin lowered the cancer stem-cell markers CD44 and CD133 and reduced colony formation.[8] In pancreatic cancer this extended in vivo: fisetin blocked the CDK1–STAT3 axis, depleting the cancer-stem-cell subpopulation and enhancing gemcitabine's effect in cells and in a xenograft.[30] This sits under Prevent Dormant Reactivation as an inferred recurrence route — reducing the stem-like, tumor-initiating population that can seed relapse — not a direct measurement of dormant disseminated tumor cells awakening, which these studies did not test.
Fisetin's Weaken classification is its best-replicated tumor-directed theme: reported suppression of the core growth-signaling pathways cancer cells depend on to proliferate — corroborated in animals, including by oral dosing in one head-and-neck model and by pancreatic xenografts — but at exposures no human oral dose has been shown to reach.
Expansion Suppression
Research concerning proliferation, cell-cycle progression, and the capacity of lesions to add durable mass.
PI3K–AKT–mTOR (signaling)
In PIK3CA-mutant colorectal cancer cells, fisetin combined with 5-fluorouracil has been reported to suppress the axis at multiple nodes — lowering PI3K, phospho-AKT, phospho-mTOR, 4E-BP1, p70S6K, Raptor and Rictor while raising phospho-AMPKα — and in a genetic Apc/Pik3ca mouse it reduced intestinal tumor incidence and multiplicity.[3] The same axis is suppressed in head-and-neck cancer,[4] in BRAF-mutant melanoma,[7] and in pancreatic cancer, where fisetin inhibited proliferation, migration and invasion through PI3K/AKT/mTOR and suppressed a xenograft.[28]
RAS–RAF–MEK–ERK (MAPK)
In BRAF-mutant melanoma, fisetin has been reported to inhibit both the MAPK and PI3K/AKT/mTOR arms — lowering phospho-MEK1/2, phospho-ERK1/2, phospho-AKT and phospho-mTOR and shifting Bax/Bak up and Bcl-2/Mcl-1 down — with fisetin plus sorafenib reducing xenograft growth more than either agent alone.[7] The MAPK evidence is melanoma-based; a lead-file claim of activity in KRAS-mutant lung cancer traced only to a review and is not carried here.
Wnt / β-catenin
In colon cancer cells, fisetin attenuated Wnt/β-catenin signaling — lowering β-catenin and TCF-4 with reduced downstream cyclin D1 and MMP-7.[2] In pancreatic cancer this extended in vivo: fisetin lowered the mitotic protein MISP, reducing nuclear β-catenin and suppressing xenograft growth.[29]
Cell cycle checkpoints (CDK4/6–RB–E2F, G1/S, G2/M)
Fisetin has been reported to arrest the cell cycle across several cancers. In head-and-neck cancer it caused G2/M arrest — lowering Cdc25C, CDK1 and cyclin B1 and raising p53 — without killing normal cells, and an oral 50 mg/kg dose inhibited a xenograft by roughly 73%.[4] It caused G2/M arrest with mitochondrial apoptosis in epidermoid carcinoma,[12] and G0/G1 arrest in leukaemia.[14]
Androgen Receptor (AR) Signalling
In androgen-receptor-positive prostate cancer, fisetin has been reported to act as an AR antagonist — competing with androgen at the AR ligand-binding domain, destabilizing the receptor and lowering its transcriptional output including PSA, and synergizing with the AR antagonist bicalutamide in LNCaP cells; in athymic mice it inhibited an AR-positive prostate xenograft (CWR22Rν1) and reduced serum PSA.[36] This is a distinct hormone-axis mechanism from the growth-signaling pathways above, and one of the cleaner target-to-phenotype chains in fisetin's evidence base, with in-vivo corroboration — though, like the rest, at exposures well above what oral fisetin reaches in people.
Fisetin's Attack classification rests on regulated tumor-cell death by several context-dependent routes — intrinsic mitochondrial apoptosis across several models (some with oral in-vivo corroboration), DNA double-strand-break damage that also underlies its tumor radiosensitisation, and an emerging, single-cancer ferroptosis signal whose direction is the mirror image of what fisetin does in normal tissue. Reactive oxygen species contribute in some models but are not required in others: the head-and-neck study with the strongest in-vivo corroboration reported cell death independent of both ROS and p53.
Direct Tumor-Directed Killing
Research concerning regulated tumour-cell death (apoptosis, ferroptosis, necroptosis).
Intrinsic apoptosis (mitochondrial / Bcl-2)
Fisetin has been reported to induce mitochondrial apoptosis across multiple cancers. In epidermoid carcinoma it lowered Bcl-2/Bcl-xL/Mcl-1 and raised Bax/Bak/Bad, collapsed mitochondrial membrane potential, released cytochrome c, and activated caspases — all blocked by a pan-caspase inhibitor.[12] It drove caspase-mediated PARP cleavage with oral in-vivo corroboration in head-and-neck cancer,[4] modulated the Bcl-2/Bax axis in an oral-dose lung-carcinogenesis model,[13] and activated caspase-3/-8/-9 in leukaemia cells.[14] In colorectal cells, lowering nuclear Nrf2 and raising ROS was the route to this apoptosis.[6]
DNA damage & repair / PARP
Fisetin has been reported to induce DNA double-strand-break damage (γH2A.X, comet assay) accompanying apoptosis in head-and-neck cancer,[4] to induce DNA damage and S-phase arrest in pancreatic cancer with xenograft corroboration and enhanced chemotherapy sensitivity,[27] and to radiosensitise colorectal cancer independent of KRAS-mutation status by inhibiting YB-1 and blocking repair of radiation-induced double-strand breaks.[17] This is a tumor-directed radiosensitising action, not host radioprotection — no normal-tissue radioprotection evidence exists.
Ferroptosis (execution / cell death)
An emerging, single-cancer signal: in osteosarcoma, fisetin has been reported to induce ferroptosis through a ROS/FOXO3-driven autophagy route, lowering SLC7A11 and reducing xenograft growth.[15] It is treated as emerging because it rests on one cancer model — and because it runs opposite to fisetin's better-documented behavior in normal tissue, where it suppresses ferroptosis via Nrf2/HO-1.[16] The direction of fisetin's redox effect is context-dependent, and this is the clearest illustration of it.
Fisetin's Protect classification is scored on host-outcome evidence, and that evidence is preclinical only: two whole-animal studies in which fisetin protected a healthy organ from a core chemotherapy drug. Its potential supportive-care role in cancer patients — improving physical function, frailty or fatigue in survivors through its senolytic action — is being tested in ongoing trials, but none has reported results, so there is no completed clinical host-outcome to score.
Other Organ-System Reserve
Research concerning renal, cardiac, pulmonary, and other non-hepatic organ reserve under stress.
Cisplatin-induced nephrotoxicity
In a rat model of cisplatin nephrotoxicity, fisetin has been reported to restore BUN, creatinine and renal histology, suppress NF-κB (p65), TNF-α, iNOS and NADPH-oxidase, and preserve Bcl-2 — importantly, without reducing kidney platinum uptake, so it did not simply block the drug's delivery.[18] This is a healthy-animal toxicity model, not a tumor-bearing one.
Doxorubicin-induced cardiotoxicity
In two independent rat studies, fisetin has been reported to attenuate doxorubicin cardiomyopathy — one via SIRT1/Nrf2-mediated suppression of ferroptosis (restored GPX4, lowered lipid-ROS; blocking SIRT1 abolished the benefit),[19] the other improving cardiac function and lowering CK-MB, LDH and caspase-3/cTn-I/iNOS/TNF-α.[20]
The tension to keep in view: both organ-protection stories attribute the benefit to an antioxidant, Nrf2-raising action — the opposite of fisetin's pro-oxidant, Nrf2-lowering action in colorectal tumor cells (see Attack and Evidence). Neither protection study used a tumor-bearing animal, so whether a host-protective dose would blunt fisetin's own anti-tumor effect is untested, though the cisplatin study's unchanged renal platinum uptake is reassuring on drug delivery.
Prevent Tumor Cell Shedding
Research concerning invasion and escape from existing lesions (EMT and ECM breach).
Fisetin reversed the invasion programme cancer cells use to spread — and, in a breast-cancer model, reduced the number of lung metastases in a live animal.
Expansion Suppression
Research concerning proliferation, cell-cycle progression, and the capacity of lesions to add durable mass.
Fisetin lowered activity in the central growth-signaling pathway across colorectal, head-and-neck, melanoma and pancreatic models, slowing proliferation.
Direct Tumor-Directed Killing
Research concerning regulated tumour-cell death (apoptosis, ferroptosis, necroptosis).
Intrinsic apoptosis (mitochondrial / Bcl-2)
Fisetin triggered tumor-cell death through the mitochondrial route across several cancers, with oral-dose animal corroboration in a head-and-neck model. Evidence is preclinical — concentration limitations apply.
Other Organ-System Reserve
Research concerning renal, cardiac, pulmonary, and other non-hepatic organ reserve under stress.
Chemotherapy organ protection
In animal studies, fisetin protected the kidney from cisplatin and the heart from doxorubicin — a preclinical host-protection signal, not yet tested in cancer patients.
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03 — Pharmacokinetics
Pharmacokinetics and Administration
For fisetin, formulation is not a footnote — it is the story. Unformulated fisetin is poorly absorbed and rapidly converted to sulfate and glucuronide conjugates whose cancer-relevant activity is poorly characterized, so unconjugated (free) fisetin in the blood is low and short-lived; the gap between what works in a dish and what an oral dose reaches in a person is the single most important thing to understand here.
Absorption
Fisetin is highly lipophilic and poorly water-soluble, and is rapidly conjugated after an oral dose, so free fisetin in plasma is low. An enhanced hydrogel formulation raised peak exposure about 24-fold in a human study.
The Concentration Gap
Laboratory studies use fisetin concentrations of 10–120 µM; the highest human plasma peak is about 0.8 µM even with an enhanced formulation — one to three orders of magnitude lower than what triggers the in-vitro effects.
Clinical Dose Context
Retail fisetin is sold at roughly 100–500 mg per dose, and senolytic research uses ~20 mg/kg/day in short courses. No oncology dose has ever been established, because no cancer-efficacy trial has been run.
Formulation Effects
A fenugreek-galactomannan hydrogel (Hybrid-FENUMAT™) produced roughly 27× higher AUC than unformulated fisetin in humans; nano- and lipid systems raise solubility and half-life in animals. None has been tested for a cancer outcome.
Metabolism
After absorption fisetin undergoes rapid glucuronidation and sulfation, and forms an active methylated metabolite, geraldol. Both fisetin and geraldol selectively inhibit the drug-clearing enzyme CYP2C8 in laboratory studies.
Co-Dosing Considerations
Medicines cleared by CYP2C8 — including the chemotherapy agent paclitaxel — warrant clinician review, since fisetin inhibits that enzyme in vitro; no human interaction has been demonstrated.
Absorption
Fisetin is highly lipophilic (logP ~3.2) and poorly water-soluble (~10 µg/mL), which limits its oral absorption.[22] After an oral dose it is rapidly and extensively conjugated: in rats, parent fisetin appeared in serum only transiently during the absorption phase, while sulfate and glucuronide conjugates predominated almost immediately.[21] The practical consequence is that free, unconjugated fisetin in the blood is low and short-lived unless an enhanced formulation is used.
The one human pharmacokinetic study measured this directly. A fenugreek-galactomannan hydrogel formulation (Hybrid-FENUMAT™, "FF-20") delivering 192 mg of fisetin produced approximately 26.9-fold higher AUC and 23.9-fold higher peak plasma concentration than 1,000 mg of unformulated fisetin, and kept free fisetin measurable in plasma out to 8 hours rather than 2.[1] This establishes that meaningfully higher systemic exposure is achievable in people — the load-bearing fact behind everything in the concentration gap below.
The Concentration Gap
This is the central pharmacokinetic fact, and it must be read against what plasma fisetin can actually reach. The cell studies underlying the Pathway Interaction Profile above used fisetin at 10–120 µM. The human study measured a peak unconjugated (parent) plasma fisetin of about 238 ng/mL — roughly 0.8 µM — even with the enhanced formulation, and only about 10 ng/mL (~0.03 µM) unformulated.[1] So even the best human oral exposure sits one to three orders of magnitude below the concentrations that produce the in-vitro effects. That is strong evidence of a translational exposure problem — but the study measured only parent fisetin and its active metabolite geraldol, not the circulating conjugates or the concentration reached inside a tumor, so the gap limits direct translation rather than proving activity is impossible.
| Benchmark | Concentration | Interpretation |
|---|---|---|
| Fisetin concentration active in cell studies | 10–120 µM | The range that produced the apoptosis, signaling-suppression and EMT effects in the pathways above |
| Human plasma peak — enhanced formulation | ~0.8 µM | The highest unconjugated (parent) plasma fisetin measured in people (238 ng/mL), with the Hybrid-FENUMAT™ hydrogel — still roughly 12- to 150-fold below the active range[1] |
| Human plasma peak — unformulated | ~0.03 µM | Total plasma peak with plain fisetin (10 ng/mL), around 25-fold lower again — and the free active fraction is lower still[1] |
Clinical Dose Context
Retail fisetin is commonly sold at 100–500 mg per dose, and higher senolytic-research regimens use around 20 mg/kg/day for short pulsed courses — but for aging and survivorship endpoints, not cancer efficacy. No oncology-specific tumor-exposure target has ever been defined, because no cancer-efficacy trial has been run. The one controlled human comparison is a reminder that milligrams on a label are not the same as exposure: a 1,000 mg unformulated dose produced far lower plasma levels than a formulation delivering only 192 mg of fisetin.[1]
| Setting | Dose | Source |
|---|---|---|
| Human PK study — enhanced formulation | 192 mg fisetin (in 1,000 mg FF-20) | 26.9× AUC / 23.9× Cmax vs. unformulated[1] |
| Human PK study — unformulated | 1,000 mg | Peak ~10 ng/mL; far lower exposure despite the higher milligram dose[1] |
| Senolytic aging / survivorship research | ~20 mg/kg/day, short courses | Aging, frailty and survivorship trials — not cancer efficacy[26] |
| Retail supplement | ~100–500 mg/day | No oncology dose established for any product |
Formulation Effects
Because fisetin's native bioavailability is poor, delivery technology dominates its real-world exposure. The clearest human evidence is the Hybrid-FENUMAT™ hydrogel, which encapsulates fisetin micelles in a fenugreek-galactomannan scaffold and produced the ~27-fold exposure increase above.[1] Preclinical nano- and lipid-based systems point the same way, though none has been tested for an oncology outcome.[22]
| Formulation | Mechanism | Reported effect | Citation |
|---|---|---|---|
| Unformulated fisetin | Reference form | Peak ~10 ng/mL; free fisetin measurable to 2 h (human) | [1] |
| Hybrid-FENUMAT™ (FF-20) | Fenugreek-galactomannan hydrogel with fisetin micelles | 26.9× AUC, 23.9× Cmax, free fisetin to 8 h (human) | [1] |
| PLA nanoparticles | Polymer nanoparticle | Half-life 3.42 vs. 1.84 h and roughly doubled exposure (rat) | [22] |
| Nanocochleates | Lipid–calcium cochleate carrier | ~141-fold higher bioavailability (preclinical) | [22] |
| Nanocrystals | Particle-size reduction | Aqueous solubility raised from ~60 to ~420 µg/mL | [22] |
Metabolism
After absorption fisetin undergoes rapid glucuronidation and sulfation.[21] It also forms a methylated metabolite, geraldol (3,4′,7-trihydroxy-3′-methoxyflavone), which is itself biologically active — in mice it accumulated in tumors above parent-fisetin levels and inhibited endothelial migration.[11] In mice, an intraperitoneal dose peaked at about 2.5 µg/mL within 15 minutes and then cleared rapidly (initial half-life ~0.09 h, terminal ~3.1 h),[11] consistent with the short free-fisetin window seen in humans.
Co-Dosing Considerations
No human drug-interaction study for fisetin exists. The considerations below rest on human-tissue in-vitro data and mechanism, and each is flagged by the most cautious guidance that evidence supports.
Discuss whether to combine, separate, or avoid fisetin and a medication with your treating oncology team or physician.
| Flag | Interaction |
|---|---|
| Caution | Medicines cleared by CYP2C8 — notably the taxane chemotherapy agent paclitaxel, and several other narrow-therapeutic-index drugs — warrant clinician review. Fisetin and its metabolite geraldol have been reported to selectively inhibit CYP2C8 in human liver microsomes, with fisetin the more potent (equilibrium dissociation constant 4.1 µM); the inhibition is reversible and not mechanism-based, and no human interaction has been demonstrated. Systemic parent-fisetin peaks (~0.8 µM formulated, ~0.03 µM unformulated) sit below that inhibition constant, so a clinically significant systemic interaction is uncertain — though gut and portal concentrations after an oral dose can be higher, which is why the flag is retained.[23] |
| Monitor | Fisetin's tumor-directed effects are partly reactive-oxygen-species-dependent, while its host-protective effects are antioxidant. How co-administered antioxidants, or pro-oxidant therapies such as radiotherapy, interact with it has not been studied clinically, so the direction of any combined effect is uncertain.[6,18] |
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04 — Onset & Washout
Onset and Washout
Fisetin's plasma clock is fast and short: free fisetin appears within about an hour of an oral dose and is largely gone within hours unless an enhanced formulation extends it. How that maps onto any biological effect is unmeasured — every timing figure below describes blood concentration or a studied dosing schedule, not a demonstrated anticancer window.
Immediate Onset
Free fisetin reaches peak blood levels within about an hour of an oral dose and clears quickly — measurable to roughly 8 hours with an enhanced formulation, but only about 2 hours without one. This describes plasma concentration only.
Steady State
The only human pharmacokinetic study was single-dose. Steady-state exposure, accumulation, and sustained target engagement have not been measured in people.
Accumulated Effect
Animal anticancer studies used repeated dosing over roughly two to four weeks. Human senolytic-research regimens use short pulsed courses — for aging and survivorship endpoints, not cancer efficacy.
Dosing Pattern in Studies
The animal studies used repeated injection or high oral doses. No human oncology dosing schedule has been established — this is how fisetin was studied, not a recommended regimen.
Washout
How long fisetin's influence can take to clear before it stops being a relevant factor for co-administered medications.
No clinically validated washout period exists. With only single-dose human pharmacokinetics, no repeated-dose disposition data, and a reversible (not mechanism-based) CYP2C8 inhibition whose in-vivo duration is unmeasured, no washout interval can be reliably calculated.
Two Distinct Clocks
Fisetin's timeline splits into two genuinely different layers: how quickly it appears in and leaves the blood, and how long any tumor-relevant change would take to show up. The second has never been measured in a person — there is no human anticancer endpoint — so the two clocks cannot be connected here.
The direct-pharmacology clock (Clock A) tracks fisetin in plasma. In the human study, formulated fisetin reached peak concentration at about 1.2 hours and unformulated at about 0.9 hours, with free fisetin measurable to 8 hours (formulated) or 2 hours (unformulated).[1] In mice, an intraperitoneal dose peaked within 15 minutes and cleared rapidly (terminal half-life ~3.1 hours).[11] That describes plasma concentration only — not target engagement, tissue levels, or how long any downstream effect persists.
| Clock A — Measured Plasma Exposure | Clock B — Downstream Anticancer Effect | |
|---|---|---|
| Onset | Fast — free fisetin peaks within about 1 hour of an oral dose | Unknown in humans — no trial has measured a tumor-tissue effect or its timing |
| Persistence | Short — free fisetin measurable ~2 h unformulated, ~8 h with an enhanced formulation | Unmeasured — animal anticancer studies used repeated dosing over two to four weeks, not single doses |
| What it covers | Measured fisetin plasma concentration only — not target engagement or tissue levels | The anticancer readouts that only exist in cell and animal models, under repeated-dosing regimens |
Because no human study has measured a tumor-directed effect, Clock B is entirely preclinical here. What the animal work establishes is that reaching an anticancer effect required sustained, repeated dosing at exposures well above what oral fisetin reaches in people — not that a particular plasma window drives a particular result.
Steady State and Accumulation
Not characterized. The one human pharmacokinetic study was single-dose, so steady-state plasma levels, accumulation, trough concentrations and continuous target engagement are all unmeasured. Humans have taken fisetin repeatedly — colorectal-cancer patients received 100 mg/day for seven weeks[31] and senolytic trials use pulsed courses — but none of those studies measured pharmacokinetics, so repeated-dose exposure has occurred without steady-state data. Animal anticancer regimens likewise used repeated dosing to produce an effect, which supports repeated administration as the studied pattern — not proof that any particular steady-state level is biologically necessary.
Dosing Pattern in Studies
Animal anticancer studies used repeated dosing over roughly two to four weeks — for example oral 50 mg/kg for 19 days in a head-and-neck xenograft, or 100 mg/kg intraperitoneally every three days for four weeks in a breast xenograft.[4,5] Human senolytic-research regimens have used short pulsed courses (for example two consecutive days), but for aging and survivorship endpoints, not cancer efficacy.[26] No oncology dosing schedule has been established, and no pulsed anticancer schedule has been tested — this describes how the compound was studied, not a recommended regimen.
Washout
No clinically validated fisetin washout period has been established. The single human pharmacokinetic study describes plasma elimination of a single dose, but the CYP2C8-interaction evidence under Co-Dosing Considerations comes from laboratory microsome studies — it does not establish a human interaction magnitude or measure how long any enzyme effect would persist. A parent compound's plasma half-life cannot be used to calculate an enzyme-interaction washout on its own, since interaction duration can depend on active metabolites (fisetin forms the active geraldol), intracellular retention, and repeated dosing — none of which has been measured for fisetin. Any decision about timing fisetin around chemotherapy, particularly a CYP2C8 substrate such as paclitaxel, belongs with the treating medical team, raised when the compound is started rather than deferred to a fixed interval.
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05 — Safety
Safety Profile
Fisetin is well tolerated in the human trials reported so far, where adverse effects have been mild and mostly gastrointestinal. But "well tolerated" is not the whole picture: human exposure is broader than a single study, oncology-specific safety is still thin, and there is an unresolved laboratory signal — fisetin damages chromosomes in cultured human cells — that a reassuring "negative Ames test" alone does not close.
Gastrointestinal effects — the most commonly reported adverse effect in human trials (occasional bloating or reduced appetite), mild and not linked to serious events.
Genotoxicity signal (laboratory only) — in cultured human cells fisetin inhibits topoisomerase II and disturbs chromosome segregation, behaving as an aneugen and clastogen. Shown at concentrations above ordinary plasma levels, not in supplement users — but unresolved.
Human exposure vs. oncology safety — repeated-dose human exposure exists (a 7-week colorectal-cancer trial; a pulsed senolytic osteoarthritis trial) with no obvious new signal, but cancer-population safety remains thin.
Pregnancy — no dedicated human reproductive-safety data were identified; in that absence, use during pregnancy should be reviewed by a clinician.
Adverse Effects and Human Exposure
Reported adverse effects are mild and mostly gastrointestinal. In the single-dose pharmacokinetic study, fisetin — formulated and unformulated — produced no significant adverse events, with only two minor gastrointestinal complaints across both arms.[1] But human exposure is not limited to that one study: colorectal-cancer patients received 100 mg/day for seven weeks with only minor changes reported,[31] and a completed randomised knee-osteoarthritis trial exposed 34 people to pulsed high-dose fisetin (~20 mg/kg/day) — adverse events occurred in 28/34 fisetin recipients versus 33/40 on placebo, and serious adverse events in 2/34 versus 2/40, with no obvious fisetin-specific pattern, though the study was small and non-oncology.[34]
Preclinical toxicology summarised in the human PK report is reassuring at the doses tested — no toxicity up to a 2,000 mg/kg single oral dose in mice, no toxic manifestations after 90 days of dietary fisetin, and a negative Ames mutagenicity test.[1] That reassurance has to be read alongside the chromosome-segregation signal below, which the Ames test (which detects gene mutations in bacteria, not chromosome-level damage in human cells) would not have caught. Drug-interaction considerations — the CYP2C8 inhibition relevant to paclitaxel — are covered once under Co-Dosing Considerations above, not restated here.
Genotoxicity and Chromosome Segregation — Laboratory Only
This is the safety consideration a "negative Ames test" can obscure. In cultured human cells (TK6 lymphoblastoid and HL60), fisetin inhibited topoisomerase IIα and induced micronuclei, behaving as an aneugen (causing whole-chromosome mis-segregation) at lower concentrations and a clastogen (chromosome breakage) at higher ones.[32] A later study in TK6 cells confirmed fisetin induced aneuploidy, hyperdiploidy and polyploidy, and its authors explicitly called for further investigation of fisetin-containing supplements.[33] This is the same topoisomerase-II mechanism that underlies fisetin's DNA-damaging action against tumor cells — a genuine double edge.
The context matters and should not be overstated: these are cultured-cell experiments, generally at micromolar concentrations above the plasma levels ordinary oral fisetin reaches, and genotoxicity has not been demonstrated in people taking fisetin. But it is an unresolved laboratory signal that belongs in an honest safety picture, not something a bacterial mutation assay resolves.
Data Gaps, Liver Safety, and Pregnancy
There is no long-term human safety dataset, no dedicated oncology-population safety study, and no dedicated human reproductive-safety study. Fisetin has no LiverTox monograph and no hepatotoxicity signal was identified in the literature reviewed — an absence of any reported drug-induced liver injury, not a positive demonstration of hepatic safety in humans. Given the reproductive-data gap, use in pregnancy or when trying to conceive should be reviewed by a qualified clinician rather than assumed safe.
06 — Sourcing
Sourcing Guide
Formulation is the biggest factor in whether a fisetin product can deliver anything close to what the research above describes — because unformulated fisetin is poorly absorbed, the choice between a plain powder capsule and an enhanced-bioavailability form changes how much free fisetin reaches the bloodstream at all. Brand quality, ease of access, and compound concentrations matter too. Our Sourcing Guide offers a curated list of products available on the retail market we found to answer all of those concerns.
Fisetin Sourcing Guide07 — Literature
References
Last reviewed: August 2026