The jury is still out on that question because many zinc studies, both those that find it beneficial and those that don't, are flawed. In studies with positive results, zinc lozenges or syrup appeared to shorten a cold by one day and seemed most effective when taken within 24 hours of the start of symptoms. Taking zinc lozenges with food may reduce side effects, such as a bad taste and nausea. Steer clear of zinc nasal spray, however, which may permanently damage your sense of smell.