Both fisetin and quercetin are being tested as senolytics — drugs that clear senescent cells linked to aging. The research has moved fast. Here's the current state of the evidence, mechanism by mechanism.
Senescent cells — cells that have stopped dividing but refuse to die — are now one of the most intensively studied targets in aging research. As they accumulate with age, they secrete a cocktail of inflammatory proteins called the senescence-associated secretory phenotype (SASP), which damages neighboring tissue, accelerates aging, and is now linked to conditions ranging from osteoarthritis and lung disease to cognitive decline and cancer.
The concept of senolytic therapy — drugs that selectively clear senescent cells — moved from speculative biology to human clinical trials faster than almost any other area in longevity medicine. Two natural compounds have been at the center of this research: fisetin and quercetin.
Quercetin's senolytic properties were first systematically described in a landmark 2015 paper by the Mayo Clinic's Kirkland and Tchkonia labs (Zhu et al., *Aging Cell*), which showed that a combination of dasatinib (a cancer drug) and quercetin (D+Q) cleared senescent cells in mouse fat tissue and improved physical function in aged mice. The D+Q combination has since become the most-studied senolytic protocol and has entered multiple human clinical trials.
Quercetin in human trials: A 2019 open-label pilot study (Kirkland et al., *EBioMedicine*) gave D+Q intermittently to patients with idiopathic pulmonary fibrosis — a senescence-driven disease — and found reductions in circulating senescent cell markers (p21, p16) and improvements in physical function over three weeks. A 2020 Mayo Clinic trial in diabetic kidney disease (Justice et al., *Journals of Gerontology*) found reduced senescent cell burden using the D+Q protocol.
The quercetin bioavailability problem. Quercetin has notoriously poor oral bioavailability — often less than 10% in standard capsule form — because it is rapidly metabolized in the gut wall and liver. This has driven the development of more absorbable forms:
The dasatinib in D+Q is a prescription oncology drug — not something you can buy over the counter. Quercetin alone (without dasatinib) shows weaker senolytic activity in isolation, and its use as a standalone senolytic (at doses practical for daily supplementation) is less well-validated than the D+Q combination.
Fisetin is a flavonoid found in strawberries, apples, and onions. It was identified as a potent senolytic in a 2018 Nature Medicine paper (Yousefzadeh et al., Mayo Clinic) that compared 10 different flavonoids for senolytic activity and found fisetin to be the most effective — reducing senescent cell burden by 25–30% in aged mice and extending median healthspan.
What made the fisetin paper notable is that it worked as a standalone compound without dasatinib — suggesting fisetin may have stronger intrinsic senolytic activity than quercetin.
Fisetin in human trials: The Unity Biotechnology and Mayo-affiliated groups launched the SToMP-AD trial (fisetin in older adults at risk for Alzheimer's disease) and the AFFIRM-LITE trial (fisetin for reducing inflammation in older adults). Both are currently ongoing or recently completed as of 2026. Early published data shows fisetin is well tolerated and reduces some circulating inflammatory markers, though definitive efficacy data from blinded RCTs is still emerging.
Cleveland Clinic fisetin protocol: The Cleveland Clinic's Aging and Cognitive Health Evaluation in Elders (ACHIEVE) research group has published interest in fisetin as a non-pharmaceutical senolytic agent. Their commonly referenced protocol (based on preclinical and early human data) uses intermittent high-dose fisetin: typically 20 mg/kg body weight for 2–3 consecutive days per month, which for a 70 kg adult is approximately 1,400 mg/day over that window. This is not a daily dose — it's designed to mimic the "pulse-dosing" approach used in animal studies.
| Factor | Fisetin | Quercetin |
|--------|---------|-----------|
| Senolytic potency (preclinical) | Stronger (top of 10 flavonoids tested) | Moderate alone; strong with dasatinib |
| Human RCT data | Emerging (trials ongoing 2026) | D+Q combination has multiple published trials |
| Bioavailability | Poor (similar to quercetin); enhanced forms under development | Poor; phytosome form improves 20x |
| Standalone vs combination | Works alone in animals; unclear in humans | Strongest evidence is as D+Q combination |
| Common dose | 100–1,400 mg (pulse dosing per Cleveland protocol) | 500–1,000 mg/day or pulse with dasatinib |
| Food sources | Strawberries, apples (low concentration) | Onions, capers, apples (moderate concentration) |
Senolytic research is moving fast, but mainstream clinical recommendations haven't caught up. Currently, senolytics are not FDA-approved treatments for any aging-related condition — they remain in the research phase. Interest is highest among:
If you prefer a food-first approach (knowing that food concentrations are far lower than supplemental doses):
Food fisetin contributes meaningfully to antioxidant and anti-inflammatory diet patterns, but reaching senolytic pulse doses through food alone is not practical. Supplementation is required for dose-relevant senolytic activity.
What is the Cleveland Clinic fisetin protocol?
The commonly referenced Cleveland Clinic-affiliated senolytic protocol uses fisetin at approximately 20 mg/kg/day for 2 consecutive days each month (pulse dosing). For a 70 kg adult, that's ~1,400 mg/day for those 2 days. This mirrors the intermittent dosing strategy shown to clear senescent cells in animal models.
Is quercetin or fisetin better for senolytics?
Fisetin showed stronger standalone senolytic activity in a head-to-head comparison of 10 flavonoids at the Mayo Clinic. Quercetin has more published human clinical data but mainly in combination with dasatinib (a prescription drug), not as a standalone compound.
What dose of fisetin should I take?
No human dose has been definitively established through a completed Phase 2 or 3 RCT. Commonly used doses range from 100 mg/day for chronic supplementation to 1,000–1,400 mg/day for 2–3-day pulse protocols (based on the Cleveland/Mayo protocol frameworks). Consult a physician before starting high-dose pulse protocols.
Do fisetin and quercetin interact with medications?
Both compounds inhibit CYP3A4 to some degree, which can affect the metabolism of certain drugs including some statins, blood thinners, and immunosuppressants. Always disclose senolytic supplement use to your physician, especially if you take prescription medications.