Zinc Gluconate Lozenges for Treating the Common Cold

IN RESPONSE:

We do not agree with Farr and colleagues that the placebo used in our study resulted in biased results favoring beneficial treatment effects of the zinc lozenges. Patients receiving zinc lozenges who reported no side effects of the medication before the end of the study reported a duration of symptoms similar to that in persons with side effects. The number of placebo and zinc recipients who believed that their medication had helped alleviate their cold symptoms did not significantly differ. No clear pattern of movement was seen regarding a patient's guesses about which medication he or she was receiving during the study. Patients guessed their group assignment from among seven choices: 1) certainly placebo, 2) probably placebo, 3) possibly placebo, 4) do not know, 5) certainly active, 6) probably active, or 7) possibly active. When the zinc and placebo groups were divided into these seven subgroups, the mean and median durations of symptoms of the zinc recipients in each subgroup were always shorter than those of the placebo recipients in the same subgroup. The study nurse saw the patients within 1 day of their reported cure, and she observed no cold symptoms. These facts, as outlined in our paper, support our beliefs that blinding appears to have been maintained during the study and that the beneficial effects of zinc gluconate lozenges are real and not due to a faulty placebo.