All eight publications since 1984 that have reported a total of 10 clinical studies of the treatment of common colds with zinc are reviewed. The reasons for the puzzling mix of diametrically opposite results in these studies are elucidated and related to independent in vitro investigations. A theoretical framework is put forth that explains the beneficial effects of zinc and that has a solid foundation based on the known molecular structures of the surface of human rhinovirus and intercellular adhesion molecule-1, the docking point for human rhinovirus present on the surfaces of cells of the nasal epithelium. The results of clinical investigations and theory suggest that consistently beneficial therapeutic effects can be expected of zinc ions from zinc gluconate with glycine in lozenges prepared according to homeopathic principles and procedures. The latest study published used an "intent to treat" statistical model, and the highly beneficial effects of zinc found in that study could not be compared directly with results from any earlier studies. Raw data from that study were therefore reanalyzed on the basis of assessable patients, and the results show an even better effect and can be compared directly with earlier findings. No side effects or adverse experiences due to zinc that were serious, disturbing, or persistent were found in any of the 10 studies.