Depending on the total dosage of zinc and the composition of lozenges, zinc lozenges may shorten the duration of common cold episodes by up to 40%, according to a study
published in the July issue of Open Respiratory Medicine Journal
Zinc lozenges are dissolved slowly in the mouth to help ease the symptoms of the common cold. Interest in the healing properties of zinc lozenges started in the early 1980s with the observation that a cold of a young girl with leukemia rapidly disappeared when she dissolved a therapeutic zinc tablet in her mouth instead of swallowing it. Since then, more than a dozen studies have been carried out to find out whether zinc lozenges are effective, but the results of those studies have diverged.
Harri Hemila, MD, PhD, of the University of Helsinki, Finland, conducted a meta-analysis of all the placebo-controlled trials that have examined the effect of zinc lozenges on natural common cold infections. Of the 13 trial comparisons identified, 5 used a total daily zinc dose of less than 75 mg, and uniformly, those five comparisons found no effect of zinc. Three trials used zinc acetate in daily doses of over 75 mg, with the average indicating a 42% reduction in the duration of colds, and 5 trials used zinc salts other than acetate in daily doses of over 75 mg, with the average indicating a 20% decrease in the duration of colds.
In several studies, zinc lozenges caused adverse effects such as bad taste; however, there is no evidence that zinc lozenges might cause long term harm. Furthermore, in the most recent trial on zinc acetate lozenges, there were no significant differences between the zinc and placebo groups in the occurrence of adverse effects, although the daily dose of zinc was 92 mg.
Dr. Hemila concluded that "since a large proportion of trial participants have remained without adverse effects, zinc lozenges might be useful for them as a treatment option for the common cold."