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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 Open Respiratory Medicine
Journal.
For treating the common cold, zinc lozenges are dissolved slowly in the
mouth. Interest in zinc lozenges started in the early 1980s from the
serendipitous 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 over a dozen studies have been
carried out to find out whether zinc lozenges are effective, but the
results of those studies have diverged.
Dr. Harri Hemila of the University of Helsinki, Finland, carried out 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, five 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. Five 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, but 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."