A randomized parallel-group two arm superiority trial with an allocation ratio 1:1, both participants and investigators blinded. The zinc lozenge that will be used in the study is a commercial product available from the University Pharmacy, Helsinki, Finland. The product is classified as a "medical device" and it is not regulated according to the jurisdiction for medicines. Each lozenge contains 13 mg elemental zinc as zinc acetate. The instruction in the commercial package for common cold patients is to dissolve slowly 6 lozenges per day in their mouth, which totals to 78 mg/day of elemental zinc, at most for 5 days. The same instruction will be used in this trial. The University Pharmacy prepared 200 placebo lozenge packages so that the placebo lozenges contain sucrose octaacetate, and they are similar with the zinc lozenges in visual appearance and in taste. 200 packages of zinc lozenges will be used as the active intervention. The packages will contain 30 lozenges (6 lozenges/day × 5 days). The packages of lozenges will be distributed to the enrolled participants in November 2017. The participants will be instructed to keep the package readily available so that, when they catch the common cold, they will find the package and they can start to take the lozenges according to the instructions. The participants will be instructed to start taking zinc lozenges as soon as they start to suffer from the first symptoms of the common cold. The participants will be instructed to take 6 lozenges daily over the time awake, evenly distributed, allowing the lozenge to dissolve in the mouth as slowly as possible. The duration of intervention is for the maximum of 5 days. If the symptoms disappear before 5 days, the participant may stop the usage of the lozenges. There will be no limitations for other treatments that participants wish to use for treating their colds. Participants will be requested to respond to a web-based symptom questionnaire daily from the first day of the treatment to the recovery from the common cold, or to a maximum of 2 weeks.
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The duration of the common cold (time to recovery)
Timeframe: 2 weeks after the start of the intervention