Depending on the total dose of zinc and the composition of lozenges, zinc lozenges may shorten the duration of common colds by up to 40 percent.

Harri Hemila, from University of Helsinki in Finland, completed a meta-analysis of placebo-controlled trials that have examined the effect of zinc lozenges on natural common cold infections. Of the 13 trial comparisons identified, five used a total daily zinc dose of less than 75 milligrams, and those five comparisons uniformly found no effect of zinc. Three trials used zinc acetate in daily doses of more than 75 milligrams, with the average indicating a 42 percent reduction in the duration of colds. Five trials used zinc salts other than acetate in daily doses of more than 75 milligrams, with the average indicating a 20 percent decrease in the duration of colds.

The researchers concluded that the study “shows strong evidence that the zinc lozenge effect on common cold duration is heterogeneous so that benefit is observed with high doses of zinc but not with low doses…. The effects of zinc lozenges should be further studied to determine the optimal lozenge compositions and treatment strategies.”

Hemila, H. (2011). Zinc lozenges may shorten the duration of colds: a systematic review. Open Respiratory Medicine Journal. 5:51-58.

—Dr. Bob Goldman