Most fisetin marketing describes it as an antioxidant that protects cells. A 2024 study in glioblastoma cells reported the opposite effect at high concentrations: fisetin broke DNA strands, switched on the cell’s DNA damage alarm, and made a chemotherapy drug more lethal [1]. The authors’ own summary is blunt: high-dose fisetin has a genotoxic potential.
That sounds alarming if you take fisetin every day, and it deserves a straight answer rather than a dismissal. The short version is that the effect is real, it was seen in cancer cells in a dish, and the concentrations involved are far above anything a person has been measured to reach from a capsule. The longer version is below, including the parts that are still unknown.
Key Takeaways
- In LN229 glioblastoma cells, fisetin at 40 to 80 micromolar caused DNA strand breaks and activated a p53 DNA damage response [1].
- Similar DNA damage has been reported in head and neck cancer cells, where fisetin killed cancer cells without killing normal cells at the concentrations tested [2].
- 40 micromolar is about 11,450 ng/mL. The highest peak plasma level measured in the first human pharmacokinetic study, from a formulated product, was 238.2 ng/mL [3].
- No study has measured DNA damage in people taking fisetin. That gap is real.
Important: This article describes laboratory research and is not medical advice. If you have cancer or are receiving chemotherapy or radiotherapy, do not take fisetin without talking to your oncology team, because its effects on DNA repair and on cancer drugs have not been tested in people. Fisetin can also affect drug-metabolising enzymes. Speak to a doctor or pharmacist first.
What the glioblastoma study found
The researchers used LN229 cells, a human glioblastoma line, and measured three things: whether the cells survived, whether their DNA was broken, and whether the cell’s damage-response machinery switched on [1]. DNA breaks were measured two ways, with the alkaline comet assay, which shows broken DNA trailing out of the nucleus like a comet tail, and with gamma-H2AX staining, which marks sites of double-strand breaks.
Fisetin was cytotoxic and induced apoptosis. In the 40 to 80 micromolar range it also caused DNA damage on both assays and activated p53, the protein that halts the cell cycle when DNA is damaged [1]. It increased the DNA damage caused by a second chemical, methyl methanesulfonate, which the authors put down, with a deliberate hedge, to presumably inhibiting DNA repair.
Combined with temozolomide, the standard first-line drug for glioblastoma, fisetin increased cell death, reduced the number of cells left senescent after treatment and showed senolytic activity against them [1]. The authors read this as a reason to test fisetin as an add-on cancer therapy in clinical trials. No such glioblastoma trial has reported.
It is not a one-off finding
A 2024 study in head and neck squamous cell carcinoma cells found the same pattern. Fisetin at 25 to 75 micromolar inhibited growth and killed the cancer cells, and the comet assay and gamma-H2AX phosphorylation again showed concentration-dependent DNA damage [2]. The same paper reports no cell death in normal cells at the concentrations tested, and a 73 percent reduction in tumour volume in mice given 50 mg/kg orally for 19 days.
An older line of work explains part of the mechanism. In human peripheral lymphocytes, which are normal white blood cells rather than cancer cells, several flavonoids caused DNA breakage by mobilising copper ions bound to chromatin and generating reactive oxygen species [4]. Fisetin ranked second of the five tested, behind myricetin and ahead of quercetin, kaempferol and galangin. In other words, the same chemistry that makes a flavonoid an antioxidant in one setting can make it a pro-oxidant in the presence of copper.
A 2026 review of fisetin’s pharmacology lists genotoxicity at relatively high concentrations among its safety considerations [5]. This is a known property of the molecule, not a fringe claim.
Putting 40 micromolar next to a real dose
Cell studies report concentrations in micromolar. Human pharmacokinetic studies report nanograms per millilitre of plasma. Converting between them takes one number, fisetin’s molecular weight of about 286.24 g/mol, so 1 micromolar is roughly 286 ng/mL.
On that basis, 25 micromolar is about 7,156 ng/mL, 40 micromolar is about 11,450 ng/mL, and 80 micromolar is about 22,899 ng/mL.
Now the human data. In the first human pharmacokinetic study, fifteen healthy volunteers took a single 1,000 mg dose of unformulated fisetin, and the peak plasma concentration was 9.97 ng/mL [3]. A formulated version reached 238.2 ng/mL. The lowest concentration that broke DNA in the glioblastoma study is therefore roughly 1,148 times the peak from 1,000 mg of plain fisetin, and roughly 48 times the peak from the formulated product.
That gap is the main reason the glioblastoma result is not a direct warning about capsules. It comes with three caveats. Plasma is not tissue, and nobody has measured fisetin concentrations inside human cells. The pharmacokinetic study measured fisetin itself and its metabolite geraldol separately, and metabolites may behave differently. And cells in a dish are exposed for hours to a steady concentration, while a dose in the body rises and falls. Our page on why oral fisetin absorbs so poorly covers the absorption side in more detail.
What animal and safety studies show
The animal record points the other way at practical doses. In the 2018 study that made fisetin famous as a senolytic, giving it to old mice reduced senescence markers, reduced age-related pathology and extended median and maximum lifespan [6]. That is not a genotoxicity test, and it does not rule out subtler effects, but it is a reassuring result at the doses used.
Formal genotoxicity testing of fisetin itself is thin. One study tested a fisetin-ruthenium complex, a modified compound rather than the supplement form, with the Ames test, chromosomal aberration test and micronucleus assay in mice, and found no mutagenic or genotoxic effect [7]. Its highest dose, 400 mg/kg, did produce organ toxicity, and that result applies to the complex, not to plain fisetin.
For the broader safety picture, including what has and has not been reported in people, see our overview of fisetin side effects.
Who should take this seriously
For a healthy adult taking a typical supplement, the cell data do not show a measured risk. Nobody has shown fisetin damaging DNA in a human body, and the concentrations involved are dozens to more than a thousand times above measured plasma levels. It is still worth knowing that the effect exists, because better-absorbed formulations narrow the gap, and high-dose pulse protocols push exposure up.
The group for whom this matters most is people with cancer. The reason fisetin is interesting to cancer researchers, that it damages DNA, may block DNA repair and adds to the effect of chemotherapy, is exactly why combining it with treatment should only happen inside a trial or with an oncologist’s agreement. Our page on fisetin and chemotherapy timing goes through the human evidence on that question, and the preclinical cancer research page covers the wider laboratory picture.
If you are deciding on a dose, our dosage guide sets out what the human trials have actually used.
Common questions
Does fisetin damage DNA?
In cancer cell studies, yes, at high concentrations. Fisetin at 40 to 80 micromolar caused DNA strand breaks in glioblastoma cells [1], and similar damage was seen in head and neck cancer cells [2]. No study has measured DNA damage in people taking fisetin.
Is the dose in a fisetin supplement high enough to damage DNA?
There is no direct evidence that it is. 40 micromolar is about 11,450 ng/mL, while the peak plasma level in the first human pharmacokinetic study was 238.2 ng/mL, from a formulated product [3]. Tissue levels in humans have not been measured.
Is fisetin an antioxidant or a pro-oxidant?
It depends on conditions. In human lymphocytes in the presence of copper, flavonoids including fisetin generated reactive oxygen species and broke DNA [4], even though the same compounds act as antioxidants elsewhere.
Should people with cancer avoid fisetin?
They should not take it without their oncology team. Fisetin increased the effect of a chemotherapy drug in glioblastoma cells and may inhibit DNA repair [1], which is a reason for caution as well as a research interest.
Has fisetin passed genotoxicity testing?
Formal testing of plain fisetin is limited. A fisetin-ruthenium complex showed no mutagenic or genotoxic effect in mice [7], but that is a modified compound, not the supplement form.
References
- Genotoxic and Cytotoxic Activity of Fisetin on Glioblastoma Cells. Anticancer Res (2024). PMID 38423634
- Fisetin induces G2/M phase arrest and caspase-mediated cleavage of p21Cip1 and p27Kip1 leading to apoptosis and tumor growth inhibition in HNSCC. Mol Carcinog (2024). PMID 38801393
- Enhanced bioavailability and pharmacokinetics of a novel hybrid-hydrogel formulation of fisetin orally administered in healthy individuals: a randomised double-blinded comparative crossover study. J Nutr Sci (2022). PMID 36304817
- Mobilization of Copper ions by Flavonoids in Human Peripheral Lymphocytes Leads to Oxidative DNA Breakage: A Structure Activity Study. Int J Mol Sci (2015). PMID 26569217
- Fisetin: a multitarget flavonol bridging oxidative stress, inflammation, aging, and cancer. Naunyn Schmiedebergs Arch Pharmacol (2026). PMID 41538057
- Fisetin is a senotherapeutic that extends health and lifespan. EBioMedicine (2018). PMID 30279143
- Assessment of toxicity and genotoxic safety profile of novel fisetin ruthenium-p-cymene complex in mice. Toxicol Res (2023). PMID 37008693
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease. Content is for informational purposes only and is not medical advice; consult a qualified healthcare provider before starting any supplement. As an Amazon Associate we earn from qualifying purchases.