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ingestible · for respiratory health & asthma

Quercetin (Flavonoid Supplement)

Reviewed by the Nimbera editorial team · Last updated May 2026

Cesarone et al. (2019), Minerva Medica, pilot registry: subjects with mild-to-moderate asthma taking quercetin phytosome (QFit) alongside standard treatment showed better daytime and nighttime symptom control, reduced rescue inhaler use, higher peak expiratory flow with less variability, and lower oxidative stress markers versus standard treatment alone. PMID: 31578841. Note: this is a pilot registry, not a blinded RCT; larger trials are needed.$20-40/month

How to use

Take 500-1000 mg of quercetin daily with a meal containing fat, as quercetin is fat-soluble and bioavailability is low from standard powders. Phytosome or liposomal formulations improve absorption significantly and are preferred. Bromelain (250-500 mg) is sometimes combined with quercetin to further enhance anti-inflammatory effects.

How it works

Quercetin inhibits mast cell degranulation and histamine release, suppresses pro-inflammatory cytokines (IL-4, IL-5, IL-13), and inhibits phosphodiesterase enzymes, producing mild bronchial smooth-muscle relaxation. It also acts as an antioxidant that reduces oxidative stress in inflamed airways.

Where to buy

Health food stores and online retailers. Look for quercetin phytosome (Thorne, Jarrow) or quercetin + bromelain combinations. Standard quercetin capsules are widely available but have poor bioavailability.

Typical cost: $20-40/month

Safety notes

Quercetin significantly potentiates warfarin - metabolites displace warfarin from serum albumin and inhibit CYP2C9, raising INR by 0.8-1.5 points; do not combine without physician oversight and frequent INR monitoring. Can raise blood levels of cyclosporine (immunosuppressant) by 30-50%, increasing risk of nephrotoxicity - avoid combination. May inhibit the thyroid hormone uptake transporter; use caution if taking levothyroxine. Avoid doses above 1000 mg/day. Insufficient safety data in pregnancy and breastfeeding - avoid. People with kidney disease should avoid supplemental quercetin.

Drug & supplement interactions

  • Always tell your doctor or pharmacist about any supplements you take.
  • Interactions can occur with prescription medications, blood thinners, and immunosuppressants.
  • Herbal remedies can affect how the body absorbs or metabolises drugs.
  • Check drugs.com interactions checker before starting.

Clinical source

Cesarone et al., Minerva Med 2019

This information is compiled from primary clinical literature and is for informational purposes only. It is not a substitute for professional medical advice. Read our full disclaimer.