Taking zinc lozenges when you have a cold might help you get better faster, cutting down how long you're sick by about one-third.
Evidence from Studies
Supporting (2)
Community contributions welcome
Zinc Lozenges Reduce the Duration of Common Cold Symptoms
The study tested zinc lozenges and found they made colds go away faster, even more than the claim said, so it supports the claim.
Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage
This study looked at zinc lozenges for colds and found they really do shorten colds by about 33%, just like the claim says.
Contradicting (2)
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Zinc acetate lozenges for the treatment of the common cold: a randomised controlled trial
This study tested zinc lozenges and found they didn't help people get over colds faster—in fact, people taking zinc recovered slower after stopping the lozenges. So it contradicts the claim that zinc lozenges reduce cold duration by 33%.
Two randomized controlled trials of zinc gluconate lozenge therapy of experimentally induced rhinovirus colds
The study tested zinc lozenges and found they did not shorten colds at all, which goes against the claim that they reduce cold duration by 33%.
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.