Zinc acetate lozenges for the treatment of the common cold: a randomised controlled trial

Abstract

Objective: To examine a commercially available zinc acetate lozenge for treating the common cold.

Design: Randomised, double-blinded, placebo-controlled trial.

Setting: Working population in Finland.

Participants: We included men and women aged ≥18 years who usually had ≥1 cold per winter. Exclusions were pregnancy, lactation, chronic runny nose or chronic cough.

Intervention: We randomised 253 participants to receive a package of lozenges to be taken if they caught the common cold. Of the 253 participants, 88 contracted the common cold and 87 were included in our primary analysis. Zinc acetate lozenges contained 13 mg elemental zinc and placebo lozenges contained sucrose octa-acetate to camouflage the taste of zinc. Instruction to use was six times per day for the maximum of 5 days.

Primary outcome: Rate of recovery from the common cold analysed by Cox regression.

Results: There was no difference in the recovery rate between zinc and placebo participants during the 10-day follow-up (rate ratio for zinc vs placebo=0.68, 95% CI 0.42 to 1.08; p=0.10). The recovery rate for the two groups was similar during the 5-day intervention, but for 2 days after the end of zinc/placebo use, the zinc participants recovered significantly slower compared with the placebo participants (p=0.003). In the zinc group, 37% did not report adverse effects, the corresponding proportion being 69% in the placebo group.

Conclusions: A commercially available zinc acetate lozenge was not effective in treating the common cold when instructed to be used for 5 days after the first symptoms. Taste has been a common problem in previous zinc lozenge trials, but a third of zinc participants did not complain of any adverse effects. More research is needed to evaluate the characteristics of zinc lozenges that may be clinically efficacious before zinc lozenges can be widely promoted for common cold treatment.

Trial registration number: NCT03309995.

Keywords: common cold; randomised trial; respiratory infections; zinc lozenges.

Figure 1

Flowchart of the trial. One participant discontinued the study on the first day and no outcome could be recorded to her; she was administered zinc lozenges. She described that over two decades ago, she had recurrent colds and a few physicians encouraged her to test taking zinc supplements. For one winter, she used zinc and did not suffer from colds, yet over the winter, she started to develop strong adverse reactions from zinc so that she could not continue taking it. Apparently, her strong reaction to the zinc lozenges of our trial were caused by some type of sensitivity generated years earlier. Two of the 45 participants in the zinc group were unable to enter follow-up data through the web-based questionnaire, but we received the primary outcome, the duration of the common cold, by email.

Figure 2

Kaplan-Meier curves describing recovery of participants from the common cold in the zinc lozenge and placebo groups among all participants (A), among 56 participants who did not report any taste or other adverse effects on any of the follow-up recordings (B) and among 31 participants who reported taste or other adverse effects on one or more of their follow-up recordings (C). In panel A, the recovery rate in the zinc group decreased significantly after the zinc lozenge treatment ended. RR, ratio for the recovery rate between zinc and placebo groups, with RR<1 indicating that recovery is faster in the placebo group. The number of patients still sick in the two groups is marked at the bottom of the figure. RR, rate ratio.