According to a meta-analysis of three randomized controlled trials published in Open Forum Infectious Diseases, zinc acetate lozenges may increase the rate of recovery from the common cold three fold. On the fifth day, 70% of the zinc lozenge patients had recovered compared with 27% of the placebo patients.
The effect of zinc acetate lozenges was not modified by age, sex, race, allergy, smoking, or baseline common cold severity. Therefore the 3-fold increase in the recovery rate from common cold may be widely applicable. While some zinc lozenges have an unpleasant taste, the zinc acetate lozenges used in these three randomized trials did not suffer from such a problem.
The dose of zinc in the three studies was between 80 to 92 mg/day. Such doses are substantially higher than the recommended daily zinc intake in the USA, which is 11 mg/day for men and 8 mg/day for women. However, in certain other controlled studies, unrelated to the common cold, zinc has been administered in doses of 100 to 150 mg/day to patients for months with few adverse effects. Furthermore, 150 mg/day zinc is a standard treatment for Wilson's disease that requires treatment for the rest of a patient's life. Therefore, it seems highly unlikely that 80-92 mg/day of zinc for one to two weeks, starting very soon after the onset of the first cold symptoms, might lead to long-term adverse effects. None of the three analyzed zinc lozenge studies observed serious adverse effects of zinc.
Even though there is strong evidence that properly formulated zinc acetate lozenges can increase the rate of recovery from the common cold by 3 fold, many zinc lozenges on the market appear to have either too low doses of zinc or they contain substances that bind zinc ions, such as citric acid. Therefore, the findings of this meta-analysis should not be directly extrapolated to the wide variety of zinc lozenges on the current market.
Although the lead author, Dr. Harri Hemilä from the University of Helsinki, Finland, suggests that the optimal formulation of zinc lozenges and the best frequency of their administration should be further investigated, he also instructs common cold patients to test individually whether zinc lozenges are helpful for them: "given the strong evidence of efficacy and the low risk of adverse effects, common cold patients may already be encouraged to try zinc acetate lozenges not exceeding 100 mg of elemental zinc per day for treating their colds."