Zinc for Colds, Lozenges and Immune Claims: What Trials and Reviews Found
What the 2024 Cochrane review and other reviews found for zinc and colds, lozenges and COVID-19, why results vary, and the safety points to know before using zinc.
Content last updated . This page has not been medically reviewed.
Quick answer
Zinc may make little or no difference to whether you catch a cold, and the best review found only low-certainty signs that zinc used as a treatment may shorten a cold that has already started. [1] Zinc nasal products are a separate safety issue and are not recommended; see Zinc nasal sprays and loss of smell. General background on zinc is on Zinc.
Evidence labels: mixed, insufficient evidence, Proper evidence not found. Amounts below are study amounts from trials, never advice.
How the sources define the question
The Cochrane review (2024) included randomized trials of any form of zinc against placebo, in adults and children, to prevent or treat the common cold or upper respiratory infection. It excluded products where zinc was combined with other minerals, vitamins or herbs. [1] The common cold is a self-limiting viral illness, so a benefit has to be measured against colds that would resolve anyway. [1]What the reviews found
| Question | What the source found | Strength |
|---|---|---|
| Does zinc prevent colds? | 15 prevention trials. Little or no reduction in risk of developing a cold (risk ratio 0.93, 95% CI 0.85 to 1.01). [1] | Low certainty |
| Does zinc shorten a cold when started as treatment? | 19 treatment trials. Colds may be shorter by about 2.4 days on average (mean difference -2.37 days, 95% CI -4.21 to -0.53), but trials differed widely. [1] | Low certainty |
| Does zinc reduce symptom severity? | Uncertain for treatment (very low certainty). [1] | Very low |
| Side effects | Non-serious side effects were probably more common with zinc used as treatment (RR 1.34). [1] | Moderate |
| Adults, all acute respiratory infections | A 2021 meta-analysis found zinc did not reduce the risk of infection but shortened symptom duration. [2] | Mixed |
| COVID-19 | A 2023 meta-analysis of four trials found no statistically significant difference in death; trials used different designs and comparators. [3] | Insufficient |
Lozenges and why results vary
Of the 34 trials, 17 used lozenges in acetate, gluconate or orotate forms; the others used capsules, dissolved powders, tablets, syrups or nasal products. Zinc gluconate was given at 45 to 276 mg a day for 4.5 to 21 days. [1] The authors note wide variation in products, add-on treatments and outcomes, and incomplete reporting, which limits conclusions. [1] NCCIH (2020) noted that oral lozenges may reduce cold duration when started within 24 hours and used for less than 2 weeks, and listed bad taste, throat irritation, nausea and diarrhea as side effects. [4] Because forms and amounts differed across trials, these results cannot be turned into advice about any product, and no form is ranked here; see Zinc forms compared.Frequently asked questions
Does zinc prevent colds?
The 2024 Cochrane review found it may make little or no difference, with low-certainty evidence. [1]
Do zinc lozenges shorten a cold?
Treatment trials suggest colds may be about 2.4 days shorter on average, but certainty is low and the trials varied widely. [1]
Does zinc help with COVID-19?
A 2023 meta-analysis of four trials found no significant difference in deaths. Evidence is insufficient. [3]
Are there side effects?
Bad taste, nausea and stomach upset were more common with zinc treatment. [1]
Is zinc "immune support" proven for healthy adults?
Proper evidence not found beyond the cold reviews above; we searched PubMed and the NCCIH cold digest.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Limits and uncertainty
- Most trials had unclear or high risk of bias in at least one area. [1]
- We read the review's published summary, not the full report, so details beyond it are not covered here.
- Trials in people with low zinc do not automatically transfer to people with adequate zinc, and the reverse. MedlinePlus says supplementation beyond the recommended dietary allowance is not recommended at this time. [5]
- Wellness-goal context: Vitamin C, vitamin D and zinc for immunity and Colds, flu and respiratory infections.
Safety and who should ask first
Large amounts of zinc may cause diarrhea, cramps and vomiting, and long-term excess can lead to copper deficiency. [5] The NHS advises no more than 25 mg a day of zinc supplements unless a doctor advises it, and says high zinc can lower copper absorption. [6] NCCIH says zinc may interact with antibiotics and penicillamine. [4] Ask a pharmacist before combining zinc lozenges with medicines, and check the total from lozenges and multivitamins (Medication interactions). Pregnancy, children, kidney or liver conditions and upcoming surgery are all reasons to talk to a clinician first. A fever that lasts, trouble breathing or a child who seems very unwell needs medical care, not a supplement.
References
- Nault D et al. Zinc for prevention and treatment of the common cold. Cochrane Database Syst Rev. 2024. PubMed 38719213. Read 2026-10-22.
- Abioye AI et al. Effect of micronutrient supplements on influenza and other respiratory tract infections among adults: a systematic review and meta-analysis. BMJ Glob Health. 2021. PubMed 33472840. Read 2026-10-22.
- Wu JY et al. The effect of zinc on the outcome of patients with COVID-19: a systematic review and meta-analysis of randomized controlled trials. J Infect. 2023. PubMed 36693569. Read 2026-10-22.
- NCCIH, The Common Cold and Complementary Health Approaches: What the Science Says (December 2020). Read 2026-10-22.
- MedlinePlus Medical Encyclopedia, Zinc in diet (review date 1/21/2025). Read 2026-10-22.
- NHS, Vitamins and minerals: Others (chromium, copper, manganese, molybdenum, selenium, salt, zinc; page last reviewed 3 August 2020). Read 2026-10-22.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.