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Background: Over the past 20 years, the use of zinc as an over-the-counter alternative therapy for the common cold has vastly grown in popularity. Recent reports of potentially permanent anosmia caused by intranasal zinc therapy warrant careful analysis of the therapeutic effects of zinc., Methods: A search of the Medline database (including articles published during 1966-2006) for studies of zinc and the common cold produced 105 published reports. Fourteen were randomized, placebo-controlled studies that examined the effect of zinc lozenges, nasal sprays, or nasal gels on naturally acquired common colds. Eleven features of experimental design affecting signal quality, chance, bias, and blinding were used to evaluate the 14 placebo-controlled studies. These criteria were validated case definition, quantifiable hypothesis, sample size calculation, randomized assignment, double blinding, proof of blinding, measurement of compliance, measurement of dropout rate, analysis by intent to treat, description of methods of analysis, and measurements of probability. Equal weight was given to each criterion, because failure to meet any one could potentially invalidate the findings of a clinical trial., Results: Four studies met all 11 criteria. Three of these studies reported no therapeutic effect from zinc lozenge or nasal spray. One study reported positive results from zinc nasal gel. Of the remaining 10 studies, 6 reported a positive effect and 4 reported no effect. Intent-to-treat analysis was the most common criterion not met., Conclusions: This structured review suggests that the therapeutic effectiveness of zinc lozenges has yet to be established. One well-designed study did report a positive effect of zinc nasal gel.

Background: Echinacea is a herbal preparation that is frequently used to treat the common cold. Spending on echinacea in the United States has risen to >300 million dollars annually., Methods: A total of 322 articles related to echinacea and colds, including 9 placebo-controlled clinical trials, were identified using the Medline and PubMed databases. Eleven features of experimental design that affect the accuracy of the measurement of features of interest, the probability of a chance relationship, bias, and blinding were used to evaluate the 9 placebo-controlled studies. The criteria were validated case definition, quantifiable hypothesis, sample-size calculation, randomized assignment, double blinding, proof of blinding, measurement of compliance, measurement of drop-out rate, analysis by intention to treat, description of the methods of analysis, and measurement of probability. Equal weight was given to each criterion, since failure to meet any one of them could potentially invalidate the findings of a clinical trial., Results: Of the 9 studies, 2 met all 11 criteria. The results of both studies were judged to be negative by the people who performed the studies. Of the remaining 7 studies, 6 were judged to have positive results, and 1 was judged to have negative results. The criterion most commonly not met was proof of blinding., Conclusions: This structured review suggests that the possible therapeutic effectiveness of echinacea in the treatment of colds has not been established.