Zinc Lozenges Show More Promise for Shortening Colds

Zinc may modestly reduce the length of a cold when taken soon after symptoms begin, according to registered dietitian Johannah Katz RD. A 2024 Cochrane review suggested that illness could end roughly two days sooner, though confidence in that finding was low because the studies differed widely in their methods, formulations and doses. The review also found no persuasive reduction in overall symptom severity.

Lozenges have stronger support than zinc tablets that are swallowed. In a 2027 analysis combining seven trials, lozenges providing more than 75mg of zinc reduced cold duration by an average of 33% versus placebo. These products dissolve gradually, distributing zinc through the mouth and throat. Researchers proposed that this could hinder cold viruses from multiplying and spreading, but that explanation has not been confirmed. Benefits have appeared with lozenges using either the acetate or gluconate form of zinc, without a significant difference between them.

Trials reporting shorter colds generally supplied about 75-90 mg of elemental zinc each day, with many using 80-92 mg/day, for under two weeks. Those quantities exceed the US adult upper intake level of 40 mg/day. NHS guidance sets a maximum of 25mg daily from supplements unless a doctor recommends otherwise. Katz said amounts beyond roughly 100 mg/day have not shown greater benefit.

Possible effects include nausea, an upset stomach and an unpleasant or metallic taste. Prolonged high intake can disrupt copper absorption and weaken immune function. Zinc may also interact with penicillamine and with tetracycline or quinolone antibiotics. Nasal zinc gels and sprays have been associated with potentially permanent smell loss. Evidence suggests zinc is more useful after symptoms start than as routine prevention, which may do little or nothing to lower the chance of catching a cold.