The trial involved 100 employees of the Cleveland Clinic, who enrolled within 24 hours of developing symptoms of the common cold. Half the participants were assigned randomly to the zinc treatment while the other half received placebo lozenges.

Participants were asked to dissolve one lozenge in their mouths every two hours while awake for as long as they had any cold symptoms. They used an average of five lozenges each per day. The zinc lozenges each contained 13.3 mg of zinc in the form of zinc gluconate. They were manufactured by the Quigley Corporation under the trade name COLD–EEZE.

The results of the trial, reported in Annals of Internal Medicine, showed a clear benefit of zinc therapy. The average time for all cold symptoms to disappear was only 4.4 days in the zinc group compaired to 7.6,days in the placebo group.

Sore throat symptoms disappeared within one day in the zinc group but took three days in the placebo group. The period of actual nasal drainage also was considerably shorter in the zinc group-four days compared to seven days in the placebo group.

In addition, the zinc group had significantly fewer days with coughing, headache and hoarseness.

There was no significant difference in the groups with regard to fever, muscle ache, scratchy throat, or sneezing.

However, zinc group participants complained of more side effects (nausea and bad taste) than did the placebo group.

Researchers speculate that zinc may prevent the replication of cold viruses, especially the rhinovirus. But they warn against long-term ingestion of zinc because it may lead to imbalances in levels of copper and other nutrients in the body.