Zinc
Zinc is a mineral your body needs for immune function, wound healing and hundreds of enzymes. Zinc lozenges started early in a cold may shorten it by about 2 days, but the evidence is low certainty, and zinc doesn't seem to prevent colds.
Zinc is an essential mineral found in some foods and sold as a supplement. It's needed for the activity of hundreds of enzymes, and it plays a role in immune function, protein and DNA synthesis, wound healing, and cell signaling and division.
Research & evidence
Strong support Some support Weak or no supportColours show how well the sources back each point. The reason is next to each one.
Zinc lozenges taken early in a cold — some individual trials started dosing within 24 hours of symptom onset — may shorten cold duration by about 2 days, per a 2024 Cochrane review rated low to very low certainty of evidence.
Limited evidenceSome support. Reviewers rated the certainty low
Study details
Low to very low certainty, per the review's own grading — based on 34 trials, 8,526 participants (2024 Cochrane review). Most trials used lozenges, though the review also covered other delivery forms. Effect on symptom duration (~2 days) is a pooled estimate with substantial variation between individual trials; effect on symptom severity is unclear. Zinc showed little to no effect on preventing colds (a separate question from treatment duration).
Source: Nault D, Machingo TA, Shipper AG, et al. "Zinc for prevention and treatment of the common cold." Cochrane Database Syst Rev. 2024 May 9;5(5):CD014914, as summarized in: NIH Office of Dietary Supplements, Zinc — Health Professional Fact Sheet, "The common cold" section. View source
Lower dietary zinc intake has been associated with higher depression risk in observational studies. Separately, zinc supplementation has shown benefit as an adjunct to antidepressant drugs in some depression studies.
Limited evidenceSome support. The source hedges (“may” or “associated with”)
Study details
The intake/depression-risk link is observational only (9 cohort/cross-sectional studies pooled; RR 0.67 for highest vs. lowest dietary zinc intake) — correlational, not causal, and measures dietary intake rather than clinical deficiency. The adjunct-supplementation finding comes from a small meta-analysis of just 5 RCTs (SMD -0.36, 95% CI -0.67 to -0.04, crossing toward null in some subgroups), and a separate 2022 meta-analysis (Yosaee et al.) found the antidepressant benefit specifically in monotherapy trials, not adjunct use.
Source: Li Z, Li B, Song X, Zhang D. "Dietary zinc and iron intake and risk of depression: A meta-analysis." Psychiatry Res. 2017 May;251:41-47. doi: 10.1016/j.psychres.2017.02.006; and da Silva LEM, de Santana MLP, Costa PRF, et al. "Zinc supplementation combined with antidepressant drugs for treatment of patients with depression: a systematic review and meta-analysis." Nutr Rev. 2021 Jan 1;79(1):1-12. doi: 10.1093/nutrit/nuaa039. View source
A 2023 systematic review concluded that zinc deficiency reduces testosterone levels and zinc supplementation improves them — though the review's evidence base is mostly animal studies (30 of 38 included papers), with only 8 human studies.
Limited evidenceWeak or no support. Mostly lab or animal studies
Study details
A narrative systematic review, not a meta-analysis; no pooled effect size or confidence interval reported. 79% of the underlying evidence (30 of 38 papers) is animal studies, not human. The review's own conclusion is not restricted to deficient individuals — it generalizes across all included studies — and explicitly states the effect "may vary depending on basal zinc and testosterone levels, zinc dosage form, elementary zinc dose, and duration." Much of the human evidence traces back to a single small 1996 study (4 young men in a deficiency-induction arm, 9 elderly men in an apparently uncontrolled before/after supplementation arm).
Source: Te L, Liu J, Ma J, Wang S. "Correlation between serum zinc and testosterone: A systematic review." J Trace Elem Med Biol. 2023 Mar;76:127124. doi: 10.1016/j.jtemb.2022.127124. View source
Dosage
| Form | Amount |
|---|---|
| Any form | Recommended daily amounts for adults: 11 mg for men and 8 mg for women. The upper limit for adults is 40 mg a day. It doesn't apply to people taking zinc as medical treatment, who should be under a doctor's care. |
Side effects
Nausea and upset stomach are common, and lozenges can change how things taste. Taking high doses for weeks can lower your copper levels.
Well documented Reported (case reports, anecdotal or one study) None reportedThe circle shows how well documented an effect is, not how serious it is. A rarely reported effect can still be serious, so always read ‘When to stop’.
| Effect | Frequency | When to stop |
|---|---|---|
| Nausea, vomiting, upset stomach or diarrheaWell documentedListed plainly by NIH, MSK or LiverTox | Common | Stop and talk to a doctor if it persists. |
| Taste changesWell documentedListed plainly by NIH, MSK or LiverTox | Common, with lozenges | Switch forms or stop if it bothers you. |
| Low copper and weakened immune functionWell documentedListed plainly by NIH, MSK or LiverTox | With high doses (50 mg or more a day for weeks) | Stop and see a doctor if you're taking high doses long term. |
Safety & interactions
Safety
Too much zinc can cause nausea, dizziness, headaches, stomach upset, vomiting and loss of appetite. Taking 50 mg or more a day for weeks can lower copper levels, reduce immune function and lower HDL ("good") cholesterol. The upper limit for adults is 40 mg a day from food and supplements. Intranasal zinc products were taken off the market after more than 130 reports of lost sense of smell.
Contraindications
MSK lists no contraindications for zinc. Its warnings: zinc above 100 mg a day may increase the risk of prostate cancer; 100–300 mg a day can cause long-term problems, including copper deficiency and a weakened immune system; and heavy use of zinc-containing denture adhesives has caused serious problems. If you take antibiotics, penicillamine, eltrombopag or iron supplements, see Drug interactions.
Drug interactions
Take the antibiotic at least 2 hours before, or 4 to 6 hours after, the zinc supplement (NIH ODS; examples: Cipro for quinolones, Achromycin/Sumycin for tetracyclines). MSK gives a different window: take zinc 2 hours before or 4 hours after these antibiotics. In a small 1975 study (7 people), tetracycline levels dropped about 30% with zinc, while doxycycline wasn't significantly affected; the study's authors described the interaction's clinical significance as limited.
Take zinc supplements and penicillamine at least 1 hour apart (NIH ODS). MSK also says zinc can make penicillamine less effective.
Thiazide diuretics — such as chlorthalidone (Hygroton, Thalitone) and hydrochlorothiazide (Esidrix, HydroDIURIL) — increase zinc excretion in urine, which decreases serum zinc concentrations. Anyone taking these medications regularly should discuss their zinc status with their health care provider.
An antacid containing polyvalent cations significantly reduced eltrombopag absorption by binding to it (chelation), so MSK advises leaving at least 4 hours between eltrombopag and any zinc-containing medication or supplement. MSK's patient page says zinc can greatly reduce eltrombopag's effectiveness.
Taking supplements with 25 mg or more of iron at the same time as zinc supplements can reduce zinc absorption and blood zinc levels (NIH). MSK says taking iron and zinc supplements together may reduce the absorption of both.
Established: stated plainly by an authoritative source. Documented: supported by case reports or trial data. Theoretical: based on mechanism, animal data, or a cautious listing. Always check with your pharmacist or prescriber.
Combining with other herbs
Avoid combining with
Which form to buy
Zinc citrate or zinc gluconate
Good choiceAbsorbed better than other forms (per NIH)
About 61% absorbed in young adults, compared with 50% for zinc oxide.
Zinc oxide
Works, with a catchWorks, but absorbed somewhat less than the leading form
Absorbed somewhat less (about 50%) than citrate or gluconate (about 61%).
Lozenges (zinc acetate or gluconate), for colds
Good choiceThe form most used in the research
Most cold trials gave zinc as acetate or gluconate lozenges.