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 US, 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.
The researchers believe that 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 analysed zinc lozenge studies observed serious adverse effects of zinc.