This review summarizes the clinical evidence for the use of several natural substances in the management of coronavirus disease 2019 (COVID-19) infection. Clinical trials have demonstrated the efficacy of quercetin, melatonin, vitamin D, curcumin, N-acetylcysteine, and zinc in people with COVID-19. Studies of natural substances have been conducted in people with mild disease (outpatients) as well as people admitted for moderate or severe COVID-19. The natural substances discussed here may have anti-inflammatory, immune-modulating, and antioxidant effects that may be particularly relevant in people experiencing COVID-19 illness.
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