You feel a cold coming on, or maybe it’s already upon you: the telltale cough, sore throat and stuffy head. You swing by the drugstore, where a shelf full of over-the-counter products containing the mineral zinc claim to be able to shorten the duration of your symptoms. The promise of relief is tempting. But is it one these products can make good on? A new analysis of studies published on zinc and cold viruses concludes that there isn’t enough evidence to say whether over-the-counter zinc treatments have any effect on preventing the common cold. For those who pop lozenges or inhale nasal spray…