Do Zinc Lozenges Shorten a Cold?
Zinc lozenges are widely sold as a cold remedy. The best evidence suggests a possible modest reduction in how long a cold lasts, but the result is uncertain and depends heavily on which studies are included.
Oral zinc lozenges started soon after symptoms begin shorten the common cold.
Possible benefit, considerable uncertainty
Oral zinc lozenges may shorten an adult cold by roughly one to two days on average. However, trial results vary widely, symptom severity does not clearly improve, and minor side effects are more common with zinc.[1]
What does that mean in plain English?
Some people taking zinc lozenges recovered sooner than people taking placebo lozenges. Other well-controlled studies found no benefit. When the results were pooled, the average favoured zinc, but the large differences between trials make that estimate unstable.[1]
The evidence is more convincing for a possible reduction in duration than for an improvement in severity. It also does not show that zinc cures the infection or that every lozenge sold in shops will have the same effect.
Timing matters, but it does not settle the question
Several trials enrolled people within 24 hours of their first symptoms, and the NIH evidence summary describes possible benefit when oral lozenges are started within that window. Different zinc salts, formulations, doses, schedules, and study methods still produced inconsistent results.[6]
What the best evidence says
Plausible Zinc may shorten the duration of an existing cold
The 2024 Cochrane review found that zinc treatment may reduce cold duration by an average of 2.37 days. This estimate came from eight randomized studies involving 972 participants.[1]
Confidence was low because the results were extremely inconsistent. Most studies also had an unclear or high risk of bias in at least one area.
Uncertain Zinc does not clearly make symptoms less severe
The Cochrane review found very low-certainty evidence for overall symptom severity. The pooled result did not establish that zinc meaningfully changes how severe a cold feels.[1]
Mixed results Individual adult trials point in opposite directions
A 1996 trial of 100 adults reported a median symptom duration of 4.4 days with zinc gluconate versus 7.6 days with placebo.[3]
A preregistered 2020 trial produced the opposite result. Among 87 participants who developed a cold, a commercial zinc acetate lozenge did not accelerate recovery; median duration was seven days with zinc and five days with placebo.[4]
Not supported Benefit has not been demonstrated in children
Why the evidence remains uncertain
The studies did not test one standard product. They used different zinc salts, lozenge ingredients, daily amounts, treatment schedules, and definitions of recovery. That makes it difficult to predict whether a particular commercial lozenge will reproduce the average result.
The 2024 review also reported that most studies were funded by organizations connected to relevant commerce or industry, or did not clearly report funding. This does not automatically invalidate a study, but it adds another reason for caution.[1]
What this does not prove
- Zinc lozenges do not appear to be a proven cure for the common cold.
- The evidence does not show a reliable reduction in overall symptom severity.
- The adult findings should not be assumed to apply to children.
- The results cannot be generalized to every zinc lozenge or formulation.
- Evidence about treating an existing cold does not prove that zinc reliably prevents colds.
Safety note
Oral zinc can cause unpleasant taste, nausea, and other gastrointestinal symptoms. Across 16 treatment studies, non-serious adverse events were more common with zinc than with placebo.[1]
Long-term high intake can contribute to copper deficiency, and zinc can interact with some medicines. Intranasal zinc products should not be used because they have been linked to severe and potentially permanent loss of smell.[6]
Key studies
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| Source | What it found | Main limitations |
|---|---|---|
| Cochrane, 2024 Systematic review, 34 trials overall; duration analysis: 8 studies, N=972 |
Zinc treatment shortened colds by an estimated 2.37 days on average. | Low-certainty evidence, extreme inconsistency, variable formulations, and risk-of-bias concerns. |
| Science et al., 2012 Systematic review and meta-analysis, 17 trials, N=2,121 |
Oral zinc shortened symptoms by 1.65 days overall; the result favoured adults but not children. | Very high inconsistency between studies; adverse effects were more common with zinc. |
| Mossad et al., 1996 Randomized double-blind trial, N=100 adults |
Median symptom duration was 4.4 days with zinc gluconate and 7.6 days with placebo. | Single relatively small trial using an intensive schedule of one lozenge every two hours while awake. |
| Hemilä et al., 2020 Preregistered randomized double-blind trial; 253 randomized, 87 in the main cold analysis |
A commercial zinc acetate lozenge did not accelerate recovery. | Relatively few randomized participants developed a cold; findings apply to the tested formulation and five-day schedule. |
| Macknin et al., 1998 Randomized double-blind trial, N=249 children |
Zinc gluconate lozenges did not significantly shorten colds. | Paediatric findings do not directly answer whether selected adult formulations may work. |
Bottom line
Zinc lozenges are plausible, not proven, as a way to shorten an adult cold. The best estimate suggests a modest reduction of roughly one to two days, but confidence is low because results differ greatly between studies.
They should not be described as a cure, a reliable way to reduce symptom severity, or a remedy shown to work for children or across all commercial formulations.
Frequently asked questions
Do zinc lozenges shorten a cold?
Possibly. The best current review found low-certainty evidence that zinc treatment may shorten a cold by about two days on average, but results varied greatly between studies.[1]
How soon were zinc lozenges started in positive studies?
Several studies and the NIH evidence summary focused on starting oral zinc lozenges within 24 hours of the first cold symptoms. This does not establish that every formulation used this way will work.[6]
Do zinc lozenges make cold symptoms less severe?
That remains unclear. The 2024 Cochrane review found very low-certainty evidence for overall symptom severity and could not establish a reliable benefit.[1]
Do zinc lozenges work for children?
Evidence in children is not convincing. A randomized trial involving 249 children found that zinc gluconate lozenges did not significantly shorten their colds.[5]
Are zinc cold remedies safe?
Oral zinc commonly causes unpleasant taste, nausea, and other digestive symptoms. Intranasal zinc products should not be used because they have been linked to severe and potentially permanent loss of smell.[6]
References
- Nault D, et al. Zinc for prevention and treatment of the common cold. Cochrane Database of Systematic Reviews. 2024.
- Science M, et al. Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials. CMAJ. 2012.
- Mossad SB, et al. Zinc gluconate lozenges for treating the common cold: a randomized, double-blind, placebo-controlled study. Annals of Internal Medicine. 1996.
- Hemilä H, et al. Zinc acetate lozenges for the treatment of the common cold: a randomised controlled trial. BMJ Open. 2020.
- Macknin ML, et al. Zinc gluconate lozenges for treating the common cold in children: a randomized controlled trial. JAMA. 1998.
- National Center for Complementary and Integrative Health. The Common Cold and Complementary Health Approaches: What the Science Says.
Disclaimer
Disclaimer: This article is for general educational information only and is not medical advice. It does not diagnose, treat, or replace care from a qualified health professional. Always speak with a qualified health professional about personal health questions, medicines, pregnancy, medical conditions, or before changing treatment.
Do not use intranasal zinc products for colds because they have been linked to severe and potentially permanent loss of smell.
