Quercetin warrants further study as potential adjuvant therapy for COVID-19, says recent research

Two recent studies have found that quercetin supplementation may be an effective adjuvant therapy for the treatment of COVID-19.

Two recent studies evaluated the efficacy of quercetin supplementation as an adjuvant therapy in COVID-19 treatment. In a prospective, randomized, controlled, open-label study, published in the International Journal of General Medicine1 152 patients with confirmed COVID-19 infection were either prescribed standard care or standard care with quercetic supplement twice daily for 30 days. Each tablet contained 500 mg of Quercetic Phytosome, an ingredient from Indena SpA (Milan, Italy), which corresponds to 200 mg of quercetin. The primary endpoints of the study were: need and length of hospitalization, need for non-invasive oxygen therapy, progression to intensive care units, and death.

Results showed statistically significant differences between the two groups. Outpatients needing hospitalization were 22 in the standard care group, compared to seven in the quercetin group, and patients needing non-invasive oxygen therapy were 15 in the standard care group compared to one in the quercetic group. No patients in the quercetin group progressed to the intensive care unit, while eight did in the standard are group, three of which died. There were no deaths in the quercetic group. When researchers took comorbidities into account, they discovered that 45 out of 76 standard care patients had comorbidities, compared to 29 out of 76 in the quercetic group, making the likelihood of hospitalization fourfold in patients receiving standard care. Among patients without comorbidities, however, researchers found that the addition of quercetic supplementation was associated with significantly lower length of hospitalization and need of oxygen therapy, compared to standard care.

Following the success of this study, a follow-up open label, randomized, controlled pilot study2 was undertaken to focus the outcomes from the initial study. In the second study, 42 outpatients with COVID-19 were prescribed either standard care or standard care with the addition of same quercetin supplement. During the two-week trial, the protocol for the quercetic group was to take three tablets of the quercetin supplement per day for the first seven days, then two per day for the remainder of the study. The primary outcomes of this second study included the time needed to become negative at the RT-PCR for SARS-CoV-2 and the course of COVID-19 symptoms.

Results showed that supplementation with quercetin significantly reduced virus persistence by 76% in the first week, compared 9.5% in the standard care group, and by the end of two weeks, all subjects in the quercetin group tested negative, while two subjects in the standard care group remained positive. When it came to symptom relief, after the first week, 57% of subjects in the quercetic group were symptom-free, compared to 19% in the standard care group.

Quercetin’s benefits have been attributed to its antioxidant and anti-inflammatory properties. “Quercetin has diverse health benefits and has been widely used as a dietary supplement to boost the body’s immune system and keep a healthy lifestyle. Tackling COVID-19 in the early-stage of infection is very crucial to minimize the severity of the disease,” says one of the studies’ researchers Amjad Khan, postdoc, DPhil, M.Sc (Oxford University), from the University of Health Sciences, Lahore, Pakistan. “The results of the two pilot clinical studies are very encouraging and deserve further clinical explorations in the context of COVID-19. Quercetin is a safe, affordable and worldwide available agent.”


  1. Di Pierro F et al. “Possible therapeutic effects of adjuvant quercetin supplementation against early-stage COVID-19 infection: a prospective, randomized, controlled, and open-label study.” International Journal of General Medicine, vol. 14 (2021): 2359-2366
  2. Di Pierro F et al. “Potential clinical benefits of quercetin in the early stage of COVID-19: results of a second, pilot, randomized, controlled and open-label clinical trial.” International Journal of General Medicine, vol. 14 (2021): 2807-2816