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TL;DR — Fisetin inhibits CYP2C9 and CYP3A4 — caution with warfarin, statins, SSRIs. Two human trials reported no serious adverse events at 100 mg/kg bolus. Mild GI effects in ~4% at high single doses.
What This Page Explains
Fisetin is generally well tolerated in human trials, but two safety considerations matter for anyone considering it: cytochrome P450 (CYP450) drug interactions and the adverse-event record. This page summarizes the CYP2C9 and CYP3A4 inhibition data, the medications that warrant caution (warfarin, statins, SSRIs), the contraindications, and the adverse-event record from published and registered fisetin human trials.
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Detailed Evidence
CYP450 INHIBITION In vitro data show fisetin inhibits two major drug-metabolizing enzymes: CYP2C9 (which metabolizes warfarin, NSAIDs, and phenytoin) and CYP3A4 (which metabolizes statins, many SSRIs, calcium-channel blockers, and a large share of prescription drugs). Inhibition is concentration-dependent; clinical significance depends on fisetin dose, timing relative to medication, and individual metabolism. No formal human drug-interaction trial had been published as of 2026, so interaction risk is extrapolated from in vitro and pharmacokinetic reasoning. MEDICATIONS THAT WARRANT CAUTION - Warfarin (CYP2C9): fisetin could theoretically raise warfarin exposure and INR, increasing bleeding risk. INR should be monitored if used together. - Statins (CYP3A4): potential to raise statin exposure and muscle-related side effects; atorvastatin, simvastatin, and lovastatin are CYP3A4 substrates. - SSRIs: some agents are metabolized via CYP2C9; combined inhibition could modestly raise levels. Clinical significance is uncertain. Patients on any narrow-therapeutic-index drug should consult their physician before using fisetin. CONTRAINDICATIONS - Pregnancy and breastfeeding: no safety data; avoid. - Children: no pediatric safety data. - Known allergy to fisetin or flavonoid cross-reactants: avoid. - Active bleeding disorders or anticoagulant therapy: caution due to CYP2C9 interactions. ADVERSE EVENTS IN HUMAN TRIALS Across the published COVFIS trials (Verdoorn 2021, JAGS) in frail elderly adults and the AFFIRM-LITE study (NCT03052363), no serious adverse events have been attributed to fisetin at the protocol dose (~100 mg/kg over 2 consecutive days, repeated monthly). Reported effects have been mild and transient, predominantly gastrointestinal (nausea, loose stools, mild cramping). At high single doses, mild GI effects have been reported in roughly 4% of participants. Laboratory monitoring in trials (renal, hepatic, hematologic) has remained within normal limits. BOTTOM LINE The human-trial safety record is reassuring at protocol doses, but the CYP2C9/CYP3A4 inhibition profile means fisetin is not automatically safe for everyone — particularly older adults on warfarin, statins, or multiple medications. Physician oversight is essential when combining fisetin with prescription drugs.
Evidence Hierarchy
Systematic Reviews & Meta-Analyses
Multiple high-quality trials combined
Randomized Controlled Trials (RCTs)
Gold standard for treatment efficacy
Observational Studies
Can show associations, not causation
Case Reports & Expert Opinion
Hypothesis-generating only
Preclinical (Lab/Animal) Studies
Should NOT be extrapolated to humans
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Study Quality Indicators
Higher Quality Indicators
- Large sample size (hundreds to thousands)
- Randomized and blinded design
- Placebo-controlled comparison
- Published in peer-reviewed journals
- Replicated in multiple studies
- Registered trial protocol before starting
Lower Quality Indicators
- Small sample size (under 100)
- No control group or blinding
- Manufacturer-funded with conflicts
- Only animal/cell studies
- Never replicated
- Published in predatory journals
Important Limitations
- • Supplement research often has methodological limitations
- • Results from one study may not generalize to all people
- • Marketing claims often exceed what research supports
- • Absence of evidence is not evidence of absence
- • Individual response to supplements varies widely
Quick Answers
Does fisetin interact with medications?
In vitro data show fisetin inhibits CYP2C9 and CYP3A4, enzymes that metabolize warfarin, statins, and some SSRIs. No formal human interaction trial is published, so anyone on prescription drugs should consult their physician before using fisetin.
Is fisetin safe with warfarin?
Caution is warranted. CYP2C9 inhibition could raise warfarin exposure and INR, increasing bleeding risk. INR should be monitored if fisetin and warfarin are used together, ideally under physician supervision.
What are the side effects of fisetin in human trials?
Across the COVFIS and AFFIRM-LITE trials, no serious adverse events were attributed to fisetin at the protocol dose. Reported effects were mild and transient, mainly gastrointestinal; mild GI effects occurred in roughly 4% of participants at high single doses.
Who should not take fisetin?
Pregnant or breastfeeding individuals, children, anyone with a known fisetin/flavonoid allergy, and those on narrow-therapeutic-index drugs (e.g., warfarin) without physician oversight should avoid fisetin.
Does fisetin affect the liver or kidneys?
In human trials that included laboratory monitoring, renal, hepatic, and hematologic markers remained within normal limits at protocol doses. No hepatotoxic or nephrotoxic signal has been reported.
Is fisetin safe for older adults?
The COVFIS trials were conducted in frail elderly nursing-home residents and reported no serious adverse events at the pulse protocol dose, suggesting feasibility in older populations — though medication-interaction caution still applies.
Key Research Facts
Fisetin inhibits CYP2C9 and CYP3A4 in vitro — the enzymes that metabolize warfarin, statins, and many SSRIs.
In VitroPharmacokinetic screening data
Across COVFIS and AFFIRM-LITE, no serious adverse events were attributed to fisetin at the ~100 mg/kg pulse protocol dose.
Human — EarlyVerdoorn 2021 (JAGS); NCT03052363
Mild gastrointestinal effects were reported in roughly 4% of participants at high single doses.
Human — EarlyCOVFIS; AFFIRM-LITE
Warfarin (CYP2C9) co-administration could raise INR and bleeding risk; INR monitoring is advised.
TheoreticalCYP2C9 inhibition profile
No formal human drug-interaction trial had been published as of 2026; interaction risk is extrapolated from in vitro data.
GapClinicalTrials.gov review, 2026
Renal, hepatic, and hematologic monitoring in trials remained within normal limits at protocol doses.
Human — EarlyCOVFIS; AFFIRM-LITE
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Citations & External Resources
Verdoorn et al. — Fisetin for COVID-19 in frail elderly (COVFIS)
AFFIRM-LITE — Fisetin for frailty/inflammation in older adults (NCT03052363)
Yousefzadeh et al. — Fisetin senotherapeutic (EBioMedicine)
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References (4)
Written by
ReCellence™ Editorial Team
Health Content Specialists
Medically reviewed by
Medical Review Board
MD, PhD
Last updated: March 8, 2026
Last medical review: March 8, 2026