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As a possible treatment for common colds, we tested zinc gluconate lozenges in a double-blind, placebo-controlled, clinical trial. One 23-mg zinc lozenge or matched placebo was dissolved in the mouth every 2 wakeful hr after an initial double dose. After 7 days, 86% of 37 zinc-treated subjects were asymptomatic, compared with only 46% of 28 placebo-treated subjects (P = 0.0005). Side effects or complaints were usually minor and consisted mainly of objectionable taste and mouth irritation. Zinc lozenges shortened the average duration of common colds by about 7 days.
Eby, G. A., Davis, D. R., & Halcomb, W. W. (1984). Reduction in duration of common colds by zinc gluconate lozenges in a double-blind study. Antimicrobial Agents and Chemotherapy, 25(1), 20–24. https://doi.org/10.1128/AAC.25.1.20