Quercetin–bromelain supplementation and clinical outcomes of COVID-19: a randomized, double-blind, placebo-controlled trial in hospitalized patients in Tunisia
RCT 244 hospitalized, severely hypoxemic COVID-19 patients in Tunisia reporting lower respiratory deterioration with quercetin + bromelain. The trial was registered retrospectively in June 2024, two years after completion, and shows signs of outcome switching: the sample size was calculated for a reduction in mortality, and the introduction frames mortality and complications as the aim. The definition of respiratory deterioration (SpO₂ falling below 94%) cannot apply to most participants, whose mean baseline SpO₂ was ~79%, and the definition of escalation is unspecified. Event counts are difficult to reconcile: 93 deaths and 68 patients on NIV, but only 37 respiratory-deterioration events and 4 intubations. A co-author is affiliated with the product’s manufacturer and authors declare no competing interests.
Bioavailability. Quercetin has low bioavailability and studies typically use advanced formulations to improve bioavailability which may be required to reach therapeutic concentrations.
This study is excluded in meta-analysis:
multiple significant issues pending author response, see discussion.
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risk of death, 14.0% lower, RR 0.86, p = 0.43, treatment 43 of 122 (35.2%), control 50 of 122 (41.0%), NNT 17.
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risk of mechanical ventilation, no change, RR 1.00, p = 1.00, treatment 2 of 122 (1.6%), control 2 of 122 (1.6%).
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risk of progression, 58.0% lower, RR 0.42, p = 0.007, treatment 11 of 122 (9.0%), control 26 of 122 (21.3%), NNT 8.1, respiratory deterioration.
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hospitalization time, 7.7% higher, relative time 1.08, p = 0.37, treatment mean 11.22 (±8.24) n=122, control mean 10.42 (±5.76) n=122.
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Effect extraction follows pre-specified rules prioritizing more serious outcomes. Submit updates
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Gargouri et al., 13 Oct 2026, Double Blind Randomized Controlled Trial, Tunisia, peer-reviewed, 9 authors, this trial uses multiple treatments in the treatment arm (combined with bromelain) - results of individual treatments may vary.
