Objective: To summarize and critique the medical literature on the use of zinc lozenges for treatment of the common cold.
Data sources: MEDLINE searches (January 1966-June 1997) identified human clinical trials on the use of zinc lozenges for the treatment of the common cold. Bibliographies were also reviewed for relevant articles.
Study selection: Double-blind, placebo-controlled trials of zinc lozenges in adults for the treatment of the common cold, with the clinical end points of reduction in duration and/or severity of cold symptoms.
Data extraction: All double-blind placebo-controlled, human clinical trials on the use of zinc lozenges for the treatment of the common cold were included.
Data synthesis: The use of zinc lozenges in the treatment of the common cold has been suggested to reduce the duration and severity of cold symptoms. Of eight double-blind, placebo-controlled trials, four found zinc lozenges to be effective, while the other four reported no difference between zinc and placebo therapy. Potential reasons for the discrepancy between the results of these trials include inadequate placebo control, formulation of the lozenge, and the dose of zinc used. Common adverse effects include unpleasant taste, mouth irritation, and nausea.
Conclusions: Treatment of the common cold with zinc gluconate lozenges, using adequate doses of elemental zinc, may be effective in reducing duration and severity of cold symptoms. The benefit appears to be maximal if the lozenges are started immediately after the onset of symptoms. The formulation of the lozenges also appears to be important because the addition of citric acid or tartaric acid may reduce efficacy due to chelation of zinc ion. Although zinc gluconate lozenges have dominated clinical trials thus far, further studies are needed to demonstrate the efficacy of zinc acetate lozenges and to determine whether their adverse effect profile is more favorable to that of zinc gluconate lozenges. Patients should play an important role in the decision-making process and must decide whether the benefit gained from treatment with zinc lozenges outweighs the potential adverse effects.