Quercetin, a plant pigment in onions, apples and tea, is an inexpensive dietary supplement studied for blood pressure, infection and aging. The most consistent finding is a small blood-pressure drop, mainly when pressure is already raised. Pairing it with a prescription cancer drug to clear worn-out cells remains unproven. Alone at usual doses, it appears well tolerated for up to three months; its main risk is interactions with common drugs. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Blood pressure | <120/<80 mmHg | Primary benefit marker |
| Serum uric acid | 3.5–7.2 mg/dL men, 2.6–6.0 mg/dL women | Expected to change |
| Serum creatinine with eGFR | 0.7–1.3 mg/dL men, 0.6–1.1 mg/dL women | Safety check: a sustained rise stops use |
| ALT | ≤29–33 U/L men, ≤19–25 U/L women | Safety check; also expected to fall in fatty liver |
| INR (only if on warfarin) | No established target for quercetin; change from own baseline within the prescriber's range | Safety check: a rise signals an interaction |
Cadence: Baseline before starting; home blood pressure weekly for the first 4 weeks, then monthly; uric acid, creatinine and ALT at 8–12 weeks, then every 6–12 months; INR 3–7 days after starting or stopping quercetin while on warfarin