Different zinc lozenges have different amounts of the active form of zinc, and only the active form fights viruses.
Evidence from Studies
Supporting (1)
Community contributions welcome
Zinc lozenges as cure for the common cold – A review and hypothesis
The study shows that only certain zinc lozenges release the active ingredient (ionized zinc) that fights colds, and it matches exactly what the claim says about how much ionized zinc is in different types.
Contradicting (4)
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Zinc acetate lozenges for the treatment of the common cold: a randomised controlled trial
The study tested zinc acetate lozenges and found they didn't help with colds, which goes against the idea that ionized zinc in these lozenges has antiviral effects.
Zinc Acetate Lozenges May Improve the Recovery Rate of Common Cold Patients: An Individual Patient Data Meta-Analysis
The study only looked at how well zinc acetate lozenges help with cold recovery, but it doesn't check if other zinc types don't work or talk about ionized zinc levels, so it doesn't support the claim.
Zinc acetate lozenges for treating the common cold: an individual patient data meta-analysis.
The study shows zinc acetate lozenges help shorten colds, but it doesn't check if other zinc products have less ionized zinc or if only ionized zinc fights viruses, so it doesn't fully support the claim.
In vitro activity of zinc salts against human rhinoviruses
The study looked at zinc salts like those in lozenges and found they don't work well against cold viruses in lab tests, which goes against the claim that ionized zinc fights viruses.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.