A study published in the Open Respiratory Medicine Journal demonstrated that the duration of common cold may be shortened by up to 40% by zinc lozenges depending on the total dosage of zinc and composition of lozenges.
Zinc lozenges are dissolved slowly in the mouth for the treatment of common cold.
Zinc lozenges invoked the curiosity of researchers in the early 80s with an unexpected observation that a young girl with leukemia was immediately relieved of her common cold on chewing and dissolving a therapeutic zinc tablet in her mouth rather than swallowing it. Although numerous studies were conducted since then to determine the effectiveness of zinc lozenges, results of those studies have diverged.
A meta-analysis of all placebo-controlled trials, in which natural common cold infections were treated with zinc lozenges, was carried out by Dr. Harri Hemila of the University of Helsinki, Finland. Amongst the 13 trial comparisons, a daily dose of less than 75 mg zinc was used in five comparisons and those 5 comparisons were consistently found to have no effect with zinc. On an average, a 42% reduction in the duration of colds was observed in 3 trials using zinc acetate at daily doses of over 75 mg. An average of 20% reduction in the duration of colds was observed in 5 trials using zinc salts other than acetates at daily doses of over 75 mg.
Although several studies have demonstrated the adverse effects, such as bad taste, caused by zinc lozenges, there is no evidence of long term harm with their use. Furthermore, the most recent trial on zinc acetate lozenges did not demonstrate any significant variation in the occurrence of adverse effects between zinc and placebo groups despite 92 mg of daily doses of zinc.
To conclude, Dr. Hemila said that zinc lozenges might be a useful treatment option for common cold since a large proportion of trial participants did not show signs of any adverse effects.