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Supplements

Zinc

An essential trace mineral where deficiency correction matters and oral lozenges may shorten a cold, but excess use can create copper deficiency and neurologic harm.

Moderate
Evidence rating
Evidence review

What the evidence says

Zinc is essential for immune function, growth, wound healing, and taste. Supplementation has a clear role in confirmed deficiency or inadequate intake, but more zinc does not continuously improve immunity and the adult tolerable upper intake level is 40 mg per day for routine total intake.[1]

For the common cold, a 2024 Cochrane review concluded that zinc may shorten an ongoing cold but probably does little or nothing to prevent one. Earlier meta-analysis estimated about 1.7 fewer days of symptoms, but heterogeneity was extreme and nausea and bad taste were more common.[2][3]

Lozenge chemistry matters because products can bind zinc and reduce release of free ions; positive high-dose meta-analyses therefore do not validate every retail lozenge. A later randomized trial of a commercial acetate lozenge found no faster recovery, illustrating the unresolved formulation problem.[4][5]

Doses of 50 mg or more for weeks can inhibit copper absorption, lower HDL cholesterol, impair immunity, and eventually cause anemia or neurologic injury. Zinc also interferes with tetracycline and quinolone antibiotics and penicillamine. Intranasal zinc should be avoided because of reports of permanent loss of smell.[1][6]

Potential benefits

  • Corrects zinc deficiency and supports normal immune, growth, and wound-healing functions.[1]
  • Oral lozenges started early may modestly shorten an ongoing common cold, depending on formulation.[2][3]

Side effects and cautions

  • Oral zinc commonly causes nausea, bad taste, stomach upset, vomiting, or loss of appetite.[3][1]
  • Chronic high doses can cause copper deficiency and neurologic harm; intranasal products may permanently impair smell.[1][6]
How we scored it

Evidence breakdown

Deficiency treatment is established; common-cold trials suggest a possible duration benefit with oral zinc, offset by heterogeneous formulations, taste and nausea, and no clear prevention effect.

Clinical relevanceHigh

Evidence covers deficiency, cold duration, toxicity, and medicine interactions.

Study qualityModerate

Many randomized cold trials exist, but formulations, doses, timing, and outcomes differ greatly.

Safety dataHigh

Acute gastrointestinal effects, copper depletion, drug interactions, and intranasal smell loss are well documented.

References

Full source list

  1. Zinc: Health Professional Fact Sheet

    NIH Office of Dietary Supplements · 2025

  2. Zinc for prevention and treatment of the common cold

    Cochrane Database of Systematic Reviews · 2024

  3. Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials

    CMAJ · 2012

  4. Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate

    JRSM Open · 2017

  5. Zinc acetate lozenges for the treatment of the common cold: a randomised controlled trial

    BMJ Open · 2020

  6. Is intranasal zinc effective and safe for the common cold? A systematic review and meta-analysis

    Journal of Primary Health Care · 2009