Fisetin is a plant compound that has attracted research interest over the past decade, particularly for its potential anti-ageing and neuroprotective effects. First isolated from the Venetian sumac tree back in 1833, it belongs to the same chemical family as quercetin and has a similar yellow colour.

I should be upfront: fisetin research is still in early stages. Most studies are in animals or test tubes, with only a handful of human trials. The hype around fisetin as a “senolytic” (a compound that clears out damaged cells) has outpaced the clinical evidence. That said, the preliminary findings are interesting enough to warrant a closer look.

What is fisetin?

Fisetin (3,3’,4’,7-tetrahydroxyflavone) is a naturally occurring flavonoid, which is a type of plant pigment responsible for many of the colours in fruits and vegetables. It belongs to the flavonol subgroup, alongside quercetin, myricetin, and kaempferol.

Where is fisetin found?

Strawberries contain the highest concentration of fisetin among common foods, with roughly 160 micrograms per gram of fruit. Other sources include:

Fruits: apples, persimmons, mangoes, kiwi, grapes
Vegetables: tomatoes, onions, cucumbers
Nuts: various tree nuts contain small amounts
Beverages: wine (from grapes)

The amount of fisetin in these foods is quite low. To get the doses used in research studies (typically 100mg or more), you would need to eat several kilograms of strawberries daily. This is why supplements have become popular, though it is worth noting that most supplement formulations have not been tested in clinical trials.

How does fisetin work?

Fisetin appears to act through several mechanisms in laboratory studies:

Antioxidant activity: Like other flavonoids, fisetin can neutralise reactive oxygen species. In test tube studies, it has shown stronger antioxidant capacity than some other common flavonoids [1].

Senolytic effects: This is where much of the recent excitement comes from. In mice, fisetin has been shown to selectively kill senescent cells, which are damaged cells that accumulate with age and release inflammatory signals. A 2018 study found fisetin reduced senescent cell markers and extended median lifespan in aged mice [2].

Anti-inflammatory properties: Fisetin appears to inhibit several inflammatory pathways, including NF-kB and various cytokines, at least in cell culture models.

The question, of course, is whether any of this translates to humans. We simply do not know yet.

What are the potential benefits of fisetin?

I have gone through the available clinical evidence. There is not much of it, frankly, and what exists is mostly from single studies with small sample sizes. Here is what the research actually shows:

1. May help with acute ischaemic stroke recovery

This is probably the strongest piece of clinical evidence for fisetin, though “strongest” is relative given how little human research exists overall.

Stroke is a leading cause of death and disability worldwide. About two-thirds of strokes are ischaemic, meaning they are caused by a blockage rather than bleeding. Treatment focuses on restoring blood flow as quickly as possible, usually through clot-dissolving drugs like rt-PA (recombinant tissue plasminogen activator).

A double-blind randomised placebo-controlled trial involving 192 patients with acute ischaemic stroke tested whether fisetin could improve outcomes when combined with rt-PA treatment. Patients received either fisetin or placebo alongside standard care over seven days [3].

The results showed that patients receiving fisetin had better stroke outcomes measured by the NIHSS score (a standard neurological assessment). Blood markers of inflammation, including MMP-2, MMP-9, and C-reactive protein, were also lower in the fisetin group.

My take: this is a properly designed trial with meaningful results. The improvement in NIHSS scores was statistically significant. However, it is a single study, and fisetin is not part of standard stroke treatment protocols. I would want to see replication before drawing strong conclusions.

Hyperuricaemia, which is elevated uric acid in the blood, affects a substantial portion of people with chronic kidney disease. When uric acid levels remain high over time, it can damage the kidneys through inflammation and fibrosis.

An animal study examined whether fisetin could prevent this type of kidney damage. Researchers induced hyperuricaemia in mice and then treated some with fisetin. The treated mice showed reduced uric acid levels, less kidney inflammation, and less fibrosis compared to untreated animals [4].

The proposed mechanism involves STAT3 and TGF-beta signalling pathways, both of which are involved in inflammation and tissue scarring.

I should be clear: this is an animal study. The doses used do not translate directly to humans, and mouse kidney physiology differs from human physiology in relevant ways. Interesting preliminary work, but nothing you should base health decisions on yet.

3. May help prevent diabetic complications (animal studies only)

Diabetes causes damage throughout the body partly through a process called protein glycation, where sugar molecules attach inappropriately to proteins. One particularly harmful form involves methylglyoxal, a reactive compound that increases substantially in people with poorly controlled blood sugar.

In diabetic mice, fisetin supplementation reduced methylglyoxal-protein adducts and appeared to protect against some diabetes-related tissue damage [5]. The researchers proposed that fisetin works by enhancing the glyoxalase system, which is the body’s natural defence against methylglyoxal.

Again, this is animal research. The jump from mice to humans involves many unknowns. People with diabetic bladder dysfunction or other diabetic complications should not view fisetin as a treatment based on this evidence.

Alcoholic liver disease progresses through several stages: fatty liver, inflammation, fibrosis, and eventually cirrhosis. Currently, there are no FDA-approved drugs specifically for liver fibrosis. Treatment relies on stopping alcohol use and managing complications.

An animal study found that fisetin improved alcohol-induced liver damage in mice. The proposed mechanisms included faster alcohol clearance, reduced oxidative stress, and correction of lipid metabolism abnormalities [6].

This fits with fisetin’s known antioxidant properties, since alcohol metabolism generates substantial oxidative stress in the liver. However, I would not recommend fisetin supplements for anyone with alcohol-related liver disease based on a single animal study.

What about senolytic effects in humans?

The Mayo Clinic has been running clinical trials testing fisetin as a senolytic in various conditions, including chronic kidney disease, frailty, and osteoarthritis [7]. Some results have been published, but the findings are mixed and the trials are small.

The basic idea is appealing: clear out damaged senescent cells, reduce chronic inflammation, potentially slow some aspects of ageing. In mice, this has worked impressively well. Whether it translates to humans remains genuinely uncertain.

I keep seeing fisetin promoted online as an anti-ageing supplement based on the mouse studies. The enthusiasm is understandable but premature. We simply do not have good human data yet.

Are there any side effects of fisetin?

At typical supplemental doses, fisetin appears to be well-tolerated in the limited human studies that exist. Reported side effects are mainly gastrointestinal: stomach upset, nausea, and occasionally diarrhoea.

However, here is the problem: we do not have long-term safety data. Most human studies have lasted weeks, not years. The safety of taking fisetin supplements regularly over extended periods is simply unknown.

Fisetin is fat-soluble and gets absorbed better with dietary fat. Some supplement formulations include lipid carriers to improve absorption, though how much this actually matters clinically is unclear.

Safety precautions (3 contraindications to note)

1. Pregnancy, breastfeeding, and children

There is no safety data for fisetin in pregnant or breastfeeding women, or in children. The prudent approach is to avoid it entirely in these groups. This is standard advice for any supplement without established safety profiles.

2. People taking blood sugar medications

Fisetin may have blood sugar-lowering effects based on animal studies. If you have diabetes or take medications that lower blood sugar, fisetin could potentially cause hypoglycaemia. This is theoretical but worth being cautious about, particularly if you are on insulin or sulphonylureas.

3. People taking other medications

Like many flavonoids, fisetin can affect drug-metabolising enzymes in the liver. This means it could potentially increase or decrease blood levels of other medications. If you take any prescription medications, discuss fisetin with your doctor before supplementing.

This is not just standard disclaimer language. Drug interactions with flavonoids are real and documented. Quercetin, which is structurally similar to fisetin, has known interactions with several drug classes.

How much fisetin should you take?

There is no established optimal dose. Human studies have used between 100mg and 1400mg daily, with higher doses typically used in senolytic protocols (intermittent high doses rather than daily supplementation).

The Mayo Clinic senolytic trials have generally used around 20mg per kilogram of body weight, taken for two consecutive days and then not again for a month or more. This intermittent dosing is based on the theory that senolytic effects do not require continuous supplementation.

For general antioxidant purposes, lower daily doses (100-500mg) are more common in supplements, though again, there is no clinical evidence establishing what dose, if any, provides meaningful benefits.

The bottom line

Fisetin is a flavonoid with genuinely interesting properties in laboratory and animal studies. The senolytic research in mice has been particularly notable. However, the human evidence is thin:

One good stroke trial showing benefit as an adjunct to standard treatment
Several ongoing trials for age-related conditions with mixed or unpublished results
No long-term safety data

If you are considering fisetin supplements, I would suggest waiting for more human trial results. The Mayo Clinic trials should provide better data in the coming years. In the meantime, eating strawberries and other fisetin-rich foods is unlikely to cause harm and may offer modest benefits through various plant compounds, not just fisetin.

For people with specific health conditions like kidney disease, urinary symptoms, or diabetes, standard medical treatments should remain the priority. Fisetin is not a substitute for evidence-based care.

9 Benefits and Side Effects of Quercetin - a closely related flavonoid with more clinical research
12 Benefits and Side Effects of Resveratrol - another plant compound studied for anti-ageing effects
26 Benefits and Side Effects of Curcumin - a different anti-inflammatory compound with more human research

References

Khan N, et al. Fisetin: a dietary antioxidant for health promotion. Antioxid Redox Signal. 2013;19(2):151-162. PubMed
Yousefzadeh MJ, et al. Fisetin is a senotherapeutic that extends health and lifespan. EBioMedicine. 2018;36:18-28. PubMed
Wang L, et al. Fisetin Prolongs Therapy Window of Tissue Plasminogen Activator by Attenuating Neuroinflammation in Ischemic Stroke. Stroke. 2019;50(11):3326-3334. PMC
Ren Q, et al. Fisetin Attenuates Hyperuricemia-Induced Nephropathy Through Inhibition of STAT3 and TGF-beta Signaling Pathways. J Agric Food Chem. 2021;69(21):5939-5950. PubMed
Maher P, et al. Fisetin lowers methylglyoxal dependent protein glycation and limits the complications of diabetes. PLoS One. 2011;6(6):e21226. PMC
Hou XL, et al. Fisetin attenuates chronic alcohol-induced liver injury in mice. Biomed Pharmacother. 2018;97:1389-1399. PMC
ClinicalTrials.gov. Search results for fisetin. National Library of Medicine. ClinicalTrials.gov
NHS. Herbal medicines: overview. NHS Website