When zinc lozenges have extra flavor ingredients like citric acid or glycine, they don't work as well for shortening colds because these ingredients stick to the zinc. Lozenges with multiple flavor additives showed no reduction in cold length, while those with just one reduced colds by over 3 days.

Different ingredients in zinc lozenges can change how well they work, even if the amount of zinc is the same, because some ingredients stick to the zinc and make it harder for your body to use it.

Certain zinc lozenges can help treat colds if they're made without ingredients like citric acid, but if those ingredients are added, the lozenges might not work because they don't release enough zinc.