Different zinc lozenges have different amounts of the active form of zinc, and only the active form fights viruses.

Different zinc lozenges let your body absorb zinc differently. Some, like zinc acetate, let you use all the zinc, while others don't let you use any at all.

Different types of zinc lozenges release zinc in different amounts when they dissolve in your mouth, and this affects how well they work in studies.

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.

Zinc lozenges might help with cold symptoms, but lab tests show zinc doesn't really fight cold viruses directly, so there's probably another reason they work.