Quercetin

Quercetin is a preclinical curiosity with no human tumour response evidence.

Small RCTs show reduced nasal symptoms; bioavailability limits real-world effect.

Quercetin stabilizes mast cells and improved allergic rhinitis symptoms in small trials — the best-evidenced natural antihistamine supplement.

Quercetin has senolytic interest but human anti-inflammatory data in ageing are preliminary.

Quercetin has plausible antiviral and mast-cell stabilising activity with weak human evidence.

Quercetin has plausible mast cell effects for allergic sinus symptoms and weak clinical data.

Quercetin is a potent antioxidant in vitro, but poor bioavailability means human trials show smaller and less consistent effects on oxidative stress markers than laboratory data suggest.

Evidence for quercetin and immune function is preliminary. A trial in cyclists found reduced post-exercise illness, but broader immune benefit and the widely promoted antiviral claims are not established in humans.

Quercetin produces small reductions in blood pressure in meta-analysis, most evident at doses above 500mg daily and in people with hypertension. Effects on lipids and clinical events are unproven.

Promising preventive layer for seasonal allergies — start before the season hits.

Plausible adjunct for antihistamine-resistant hives; evidence is early.

Quercetin is the best-studied supplement in chronic pelvic pain syndrome, with two positive randomised trials — a genuine evidence-based adjunct for the most common and most treatment-resistant form of prostatitis.

Quercetin, a natural mast-cell stabiliser, has small trials reducing allergic rhinitis symptoms — the most common driver of post-nasal drip — making it a reasonable seasonal adjunct, though nasal steroid sprays and saline rinses have far stronger evidence.

Quercetin has modest evidence for allergic congestion specifically — small trials show reduced allergy symptoms — but it will not unblock a cold, and saline rinses plus steroid sprays have far stronger data for congestion relief.

Plausible on paper, untested for MCS, and aimed at a mechanism MCS has never been shown to involve.

Plausible mechanism, minimal quality human data; butterbur (PA-free) has better trial support among supplements.

Quercetin lowers CRP in meta-analysis, particularly at doses above 500mg daily and in people with elevated baseline inflammation. Bioavailability is poor and translation of biomarker change into clinical benefit is unproven.

Mechanistically plausible but human trial evidence is lacking — an optional add-on, nothing more.