Zinc and the common cold

Zinc supplements (frequently zinc acetate or zinc gluconate lozenges) are a group of dietary supplements that are commonly used in an attempt to treat the common cold.^[1] Evidence suggests that zinc does not prevent colds but may reduce their duration, with minimal or no impact on symptom severity.^[2][3] Adverse effects with zinc supplements by mouth include bad taste and nausea.^[1] The intranasal use of zinc-containing nasal sprays has been associated with the loss of the sense of smell;^[1] consequently, in June 2009, the United States Food and Drug Administration (USFDA) warned consumers to stop using intranasal zinc.^[1]

Zinc gluconate 50 mg tablets (GNC brand)

The human rhinovirus – the most common viral pathogen in humans – is the predominant cause of the common cold.^[4] The hypothesized mechanism of action by which zinc reduces the severity and/or duration of cold symptoms is the suppression of nasal inflammation and the direct inhibition of rhinoviral receptor binding and rhinoviral replication in the nasal mucosa.^[1]

Effectiveness

A 2024 Cochrane Review found little to no evidence that zinc prevents the common cold or reduces symptom severity, though it may modestly shorten the duration of symptoms. Zinc lozenges were associated with a reduction in cold duration, but the evidence was of low certainty and varied across studies.^[2]

A 2022 review observed that zinc lozenges may reduce cold duration, but the effect on symptom severity and cold prevention was minimal. The review highlighted that zinc's effect varied depending on the initial length of the cold, with longer colds experiencing greater reductions in duration.^[3]

A 2021 systematic review and meta-analysis on respiratory tract infections found that zinc modestly reduced symptom severity by day 3 and shortened illness duration by about two days, though the evidence was of low to very low certainty. Zinc offered minimal benefit in preventing infections and was associated with an increased risk of mild side effects, such as nausea and irritation.^[5]

Interactions

Some lozenge formulations do not contain enough zinc to effectively reduce the lengths of colds; some of them contain ingredients that bind zinc, like citric acid, which prevent the zinc from working.^[6]

Safety

There have been several cases of people using zinc nasal sprays and suffering a loss of sense of smell.^[1] In 2009 the US Food and Drug Administration issued a warning that people should not use nasal sprays containing zinc.^[1]

Excessive zinc intake may result in an unpleasant taste and/or nausea.^[1][7]

Mechanism of action

The hypothesized mechanism of action by which zinc reduces the severity and/or duration of cold symptoms is the suppression of nasal inflammation and the direct inhibition of rhinoviral receptor binding and rhinoviral replication in the nasal mucosa.^[1] Zinc has been known for many years to have an effect on cold viruses in the laboratory.^[8] In the arteriviridae and coronaviridae families of virus that also cause the common cold, in vitro studies found that zinc ionophores block the replication of those viruses in cell culture.^[9]