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Fisetin is a plant flavonoid that has become one of the most talked-about longevity supplements. The interest comes from a 2018 mouse study that identified fisetin as the most potent senolytic among ten flavonoids tested [1]. A senolytic clears senescent cells — the damaged, dysfunctional cells that accumulate with age and drive tissue decline.
Here is the honest picture. Fisetin's biology looks promising in mice. Every published human trial of fisetin as a senolytic is still running. The dose used in those trials is not the dose on most fisetin capsules. And even the best-absorbed fisetin formulation delivers plasma concentrations just below the senolytic window seen in the lab. This guide walks through what the evidence actually shows, where the marketing overreaches, and how a clinician would think about fisetin today.
What is fisetin?
Fisetin is a flavonol — a subclass of the flavonoid group of plant polyphenols. Its chemical name is 3,3′,4′,7-tetrahydroxyflavone. It gives the yellow colour to the smoke bush (Rhus cotinus), and it occurs naturally in strawberries, apples, persimmons, onions, grapes, and cucumbers [2].
The average daily dietary intake of fisetin is around 0.4 mg per day. A typical supplement capsule contains 100 to 500 mg. That is 250 to 1,250 times more fisetin than a person would get from food.
Fisetin appears in supplements because of three properties. It scavenges free radicals as an antioxidant. It suppresses inflammatory signalling. And most importantly for the longevity market, it selectively kills senescent cells in the laboratory dish [1] [3].
Supplement fisetin usually comes from smoke tree extract or fustic wood, not from strawberries. The extraction process concentrates the compound thousands of times above dietary levels.
For a full breakdown of fisetin chemistry, sources, and the difference between dietary and supplement fisetin, see our article on what fisetin is.
How does fisetin work in the body?
Fisetin has four proposed mechanisms. Three are well established in cells. One is the reason people take it as a longevity supplement.
Senolytic activity
Senolytics are drugs and natural compounds that selectively kill senescent cells. Senescent cells are damaged cells that stop dividing but do not die. They accumulate with age. They secrete inflammatory signals that damage nearby tissue. This inflammatory secretion is called the senescence-associated secretory phenotype, or SASP.
Fisetin interferes with the survival pathways that keep senescent cells alive. In the founding 2018 paper, fisetin killed senescent human cells at 5–20 μM concentrations while leaving healthy cells intact [1]. Aged mice fed fisetin cleared senescent cells in fat, spleen, liver, and kidney tissue. Their median lifespan increased.
Read the deeper story in our article on fisetin as a senolytic.
SASP suppression
Fisetin also suppresses the inflammatory secretions from senescent cells. This is called senomorphic activity. Some formulations of fisetin — including certain liposomal versions — shift its pharmacology from senolytic clearance to senomorphic suppression [4]. That is a mechanistic change, not just a dose change.
Antioxidant and Nrf2 activation
Fisetin scavenges free radicals directly. It also activates the Nrf2 pathway, which turns on the body's own antioxidant defences [2].
Brain penetration
Fisetin can cross the blood-brain barrier in animal studies. This is unusual for a flavonoid and explains the interest in fisetin for cognitive function [5].
What does the fisetin evidence actually show?
The evidence for fisetin's benefits sits at four tiers of strength. Tier 1 is multiple large human trials with consistent results. Tier 4 is mechanistic laboratory data. Every claim about fisetin currently sits at Tier 3 or below.
Senescent cell clearance in mice — Tier 3
Fisetin reduced senescent cell burden in multiple mouse studies [1]. A 2025 study showed fisetin's effect on frailty and grip strength in aged mice matched the effect of genetic senescent cell clearance and matched a synthetic senolytic drug [6]. That head-to-head equivalence in mice is a striking result.
Human trials — still ongoing
Six clinical trials of fisetin are currently running or completed but unpublished. The AFFIRM trial at the Mayo Clinic tests fisetin for frailty in older women [7]. Others test fisetin for post-COVID recovery, knee osteoarthritis, breast cancer survivorship, and long-COVID cognitive symptoms. None have published efficacy results yet.
One published human trial — COVID-FIS — used fisetin in nursing home residents with COVID-19 [7]. It reported the intervention was safe. It did not report a clear clinical benefit.
Comprehensive review — Tavenier 2024
The most complete review of fisetin as a senotherapeutic was published in 2024 [8]. Its conclusion is measured: fisetin shows senolytic activity in cells and animals, ongoing human trials will determine clinical translation, and low bioavailability may limit its usefulness in humans.
Other claimed benefits
Fisetin is marketed for cognitive function, skin health, hair growth, joint pain, and cardiovascular health. Each claim rests on preclinical evidence. See our deeper article on fisetin benefits for the tier grading of each specific claim.
How well is fisetin absorbed?
Fisetin has poor oral bioavailability. This is the most important thing to understand about the supplement.
The only published human pharmacokinetic study gave 15 healthy adults 1,000 mg of unformulated fisetin in one arm and a hydrogel-encapsulated formulation in the other [9]. Peak plasma fisetin from the unformulated dose was only 10 ng/ml — about 35 nanomolar. The senolytic effect in the laboratory dish requires 1 to 5 micromolar, roughly 30 to 150 times higher than that plasma peak.
The encapsulated formulation improved things. Dose-normalised, peak concentration was 24 times higher. Total exposure was 27 times higher. Fisetin remained detectable in blood for 8 hours instead of 2 hours.
Even so, peak fisetin from the best-formulated version reached about 0.83 μM. That is still just below the low end of the senolytic window.
The Krishnakumar 2022 study was funded by the company that owns the tested formulation. Four of six authors were company employees. We flag this because independent replication is still pending.
For the full breakdown of fisetin absorption biology and formulation options, see our article on fisetin bioavailability.
What is the right dose of fisetin?
Every published human trial of fisetin as a senolytic uses the same dose. The dose is 20 mg per kilogram of body weight, given once daily for two consecutive days, then nothing for one month. This is called the pulsed protocol or the hit-and-run schedule.
For a 70 kg adult, 20 mg/kg is 1,400 mg. Two days on. Twenty-eight days off. Then repeat.
Almost every commercial fisetin capsule is sold for daily use at 100 to 500 mg per day. That daily-capsule format matches no published trial of fisetin as a senolytic.
The pulsed protocol makes biological sense. Senescent cells are hard to kill because they resist apoptosis. Fisetin appears to interfere with several survival pathways at once, but only when the plasma concentration is high enough. Two consecutive days of high dosing may be enough to push senescent cells past the survival threshold. Continuous low dosing may keep the plasma concentration too low to hit that threshold.
See our fisetin dose article and our detailed breakdown of the Mayo Clinic pulsed protocol for the full picture.
How should you take fisetin?
Three practical rules based on the pharmacokinetic data.
Take fisetin with a fat-containing meal
Fisetin is fat-soluble. Absorption improves substantially when it is taken with dietary fat. Yoghurt, nut butter, avocado, or olive oil in a meal are all sufficient. Taking fisetin on an empty stomach is the least efficient way to absorb it.
Take fisetin in the morning
All published trial protocols administer fisetin in the morning. Fisetin has mild anti-inflammatory activity that may cause slight drowsiness in some people. Morning dosing gives the body all day to handle any subtle sedative effect.
Choose a formulation that matches your protocol
If you follow the pulsed senolytic protocol, you need enough capsules per pulse to hit 20 mg/kg. If you take daily lower doses, a smaller-capsule product is fine. Formulation matters more than raw dose. See our article on liposomal fisetin and formulation choice.
For the full timing and pairing guidance, see our article on how to take fisetin.
Is fisetin safe?
Fisetin has a reassuring general safety profile in the short-term pulsed protocols used in published trials. No serious adverse events have been reported.
Long-term safety of daily fisetin at commercial capsule doses over months and years has not been formally studied in a controlled trial.
Common side effects
Mild gastrointestinal upset is the most common report. Some users report headache, fatigue, or mild sleep disturbance. Discontinuing the supplement resolves these effects in most cases.
Is fisetin bad for the liver?
No. Fisetin has shown liver-protective effects in animal studies, not liver toxicity. Patients with existing liver disease should still consult their doctor before starting any supplement.
Drug interactions
Fisetin is metabolised by cytochrome P450 enzymes. Theoretical drug interactions exist with:
- Warfarin and direct oral anticoagulants (DOACs)
- Antiplatelet drugs like aspirin, clopidogrel, and ticagrelor
- Tyrosine kinase inhibitors used in cancer treatment
- Chemotherapy agents
- Immunosuppressants
Patients on any of these medications should speak with their prescriber before starting fisetin. See our full article on fisetin drug interactions.
Who should avoid fisetin
Fisetin should not be started during pregnancy, breastfeeding, or an active malignancy without specialist guidance. See our articles on fisetin in pregnancy and the full fisetin safety profile.
How does fisetin compare to other flavonoids?
Longevity supplement shelves carry several plant-derived compounds with overlapping claims. Fisetin sits alongside quercetin, spermidine, urolithin A, resveratrol, and apigenin. Each targets a different aspect of ageing biology.
Fisetin vs quercetin
Both are flavonoids with similar structures. Fisetin is more potent as a standalone senolytic in mouse studies. Quercetin has more human trial data overall, mostly in combination with the prescription drug dasatinib. See our fisetin vs quercetin comparison.
Fisetin vs urolithin A
Urolithin A is a mitophagy inducer — it helps cells recycle damaged mitochondria. Fisetin clears senescent cells. Different mechanisms, potentially complementary. Urolithin A has arguably stronger human evidence on muscle function endpoints. See our fisetin vs urolithin A comparison.
Fisetin vs spermidine
Spermidine is an autophagy inducer — a different mechanism entirely. Spermidine has more human epidemiological and trial data than fisetin. See our fisetin vs spermidine comparison.
Fisetin vs resveratrol
Resveratrol is a sirtuin activator with a long trial history of mixed results. Fisetin's senolytic mechanism is distinct. See our fisetin vs resveratrol comparison.
Fisetin vs apigenin
Apigenin inhibits CD38, an enzyme that consumes NAD+. Fisetin does not. See our fisetin vs apigenin comparison.
What foods are highest in fisetin?
Strawberries top the food-source list at around 160 μg per gram. A large 200 g serving of strawberries provides about 32 mg of fisetin. Apples come next at 26.9 μg/g. Persimmons contain around 10.6 μg/g. Onions, grapes, cucumbers, lotus root, and kiwi contain smaller amounts.
Even a strawberry-heavy diet delivers far less fisetin than a single supplement capsule. A 100 mg fisetin capsule contains roughly 625 g of strawberry equivalent. A 500 mg capsule contains about 3.1 kg of strawberry equivalent.
Whether dietary fisetin produces any senolytic effect is unknown. The human evidence for senolysis comes from supplement-level doses, not dietary intake. Strawberries remain worth eating for their broader flavonoid, vitamin C, and fibre content. See our article on foods high in fisetin.
What we still do not know about fisetin
Five open questions matter more than any other.
Does fisetin work as a senolytic in humans? The AFFIRM trial and the other five running trials will tell us. Until they publish, this is the central unknown.
What is the right human dose? Every trial uses 20 mg/kg × 2 days. That number is extrapolated from mouse data. It has not been optimised in dose-ranging human studies.
Does formulation matter for the senolytic effect? Better absorption produces higher plasma concentrations, but at least one liposomal formulation appears to convert fisetin from a senolytic to a senomorphic. Which effect readers want is not obvious.
Is chronic dosing safe? All safety data on fisetin comes from short pulsed protocols. The long-term safety of daily commercial capsules over years has not been characterised.
Which conditions respond best? Ongoing trials cover frailty, osteoarthritis, post-COVID syndrome, and cognitive endpoints. Real-world efficacy may vary by condition and by patient.
Bottom line
Fisetin's senolytic biology is real. The mouse data are strong. Human trials are running but have not yet published results. Every commercial fisetin capsule dosed daily sits outside the trial-validated protocol. Absorption is poor even with the best formulation. Safety looks reassuring in the short term but is not established for chronic daily use.
If you decide to try fisetin, take it with a fat-containing meal in the morning. If you follow the pulsed senolytic protocol, plan the dose to hit 20 mg/kg on two consecutive days each month. If you take daily capsules, know that the format matches no completed trial. Discuss any use with your doctor if you are on prescription medication, pregnant, breastfeeding, or being treated for cancer.