Tier 4 — mechanistic

Safety Aspects of the Use of Quercetin as a Dietary Supplement

Andres S, Pevny S, Ziegenhagen R, Bakhiya N, Schäfer B, Hirsch-Ernst KI, Lampen A
Molecular Nutrition & Food Research 2018 62(1):1700447

Bibliography

PubMed
PMID 29127724
DOI
10.1002/mnfr.201700447

Study snapshot

DesignNarrative review
ModelReview of human intervention studies and animal data on isolated quercetin supplement safety
SampleNot applicable — narrative safety review, no newly recruited participants.
InterventionNot applicable — review of quercetin supplement safety studies; no fisetin intervention.
DurationNot applicable to review; included human studies varied in length.
EndpointsQuercetin adverse effects and tolerability; Higher-dose and long-term safety limitations; Potential interactions and risks in susceptible populations

What the study showed, in plain terms

This German food-safety authority review examines what's known about the safety of quercetin taken as a standalone supplement, often at doses of up to 1,000 mg per day — well above what people get from food. Short-term studies rarely report anything beyond mild side effects. But the review is clear that solid long-term safety data (more than 12 weeks of high-dose use) don't yet exist, and flags some specific concerns worth knowing about: quercetin may worsen kidney damage in people with existing kidney disease, may promote tumour growth in some hormone-sensitive cancers in animal models, and can alter how the body handles certain other drugs.

Key findings

Adverse effects from supplemental quercetin are rarely reported and generally mild in published human intervention studies. However, adequate safety data for long-term use (over 12 weeks) at high doses (1,000 mg or more) are not currently available. Animal studies raise theoretical concerns about nephrotoxicity in pre-damaged kidneys and tumour promotion in oestrogen-dependent cancers. Human and animal studies show quercetin can alter the bioavailability of co-administered drugs.

What this study can and cannot tell us

Narrative review, not primary data, and does not evaluate fisetin. The review itself notes that long-term high-dose human safety data for quercetin are limited — use to characterise the general quercetin safety picture, not as a substitute for fisetin-specific safety information.

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Dr. Khaled Mahmoud, MBBChCritical Care Medicine, Longevity Science & Editorial Direction Dr. Amr Yasser, PhDCardiometabolic, Musculoskeletal, Gut & Bioavailability