AimsThe aim of this study was to determine whether the allergy status and other characteristics of common cold patients modify the effects of zinc acetate lozenges. MethodsWe had available individual patient data for three randomized placebo-controlled trials in which zinc acetate lozenges were administered to common cold patients. We used both one stage and two stage meta-analysis to estimate the effects of zinc lozenges. ResultsThe total number of common cold patients was 199, the majority being females. Eighty percent of them fell into the age range 20-50years. One third of the patients had allergies. The one stage meta-analysis gave an overall estimate of 2.73days (95% CI 1.8, 3.3days) shorter colds by zinc acetate lozenge usage. The two stage meta-analysis gave an estimate of 2.94days (95% CI 2.1, 3.8days) reduction in common cold duration. These estimates are to be compared with the 7day average duration of colds in the three trials. The effect of zinc lozenges was not modified by allergy status, smoking, baseline severity of the common cold, age, gender or ethnic group. ConclusionSince the effects of zinc acetate lozenges were consistent between the compared subgroups, the overall estimates for effect seemed applicable over a wide range of common cold patients. While the optimal composition of zinc lozenges and the best frequency of their administration should be further investigated, given the current evidence of efficacy, common cold patients may be encouraged to try zinc lozenges for treating their colds.