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Research · Supplements

Zinc

Zinc taken once a cold starts was linked to shorter colds in pooled trials, at low certainty and with high heterogeneity. Taken to prevent colds, it made little or no difference. Fasting glucose and HbA1c fell in pooled trials. Nausea and other minor effects rose during treatment. Long-term excess intake has caused copper deficiency.

Add to Bio HackChecked 2026-11-09
Status
Dietary supplement in the US. Some zinc cold products are sold as homeopathic drugs.
Also called
zinc gluconate, zinc acetate, zinc picolinate, zinc citrate, zinc sulfate, zinc orotate, zinc lozenges, ZMA, Zicam
Taken for
colds, immunity, infections, testosterone, blood sugar, skin, wound healing, taste, smell, recovery, period pain, PMS

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help6

Reported risks3

What people take it for, and what was found

Shown to help6

Moderate

Length of a cold, zinc started at onset

Shown to shorten colds about 2.4 days when started at onset, in low-certainty evidence from children and adults.

The numbers and sources
Effect
In treatment trials, zinc shortened colds by a mean 2.37 days (95% CI -4.21 to -0.53, I² 97%, 8 studies, 972 participants, low certainty) [1]. In 7 lozenge trials using more than 75 mg a day, colds were 33% shorter (95% CI 21% to 45%). Acetate and gluconate lozenges did not differ significantly, and 192 to 207 mg a day did not outperform 80 to 92 mg a day [2].
Population
34 trials with 8,526 children and adults [1]; 575 adults with natural colds [2].
Sources
[1], [2]
Caveats
Heterogeneity was very high and most trials were at unclear or high risk of bias [1]. The single-author lozenge analysis [2] selected trials by dose.
Moderate

Blood sugar

Shown to lower fasting glucose about 14 mg/dL and HbA1c about 0.55% in people with and without diabetes.

The numbers and sources
Effect
Across 32 placebo-controlled interventions (1,700 participants, 14 countries), zinc lowered fasting glucose by 14.15 mg/dL (95% CI -17.36 to -10.93), 2-hour glucose by 36.85 mg/dL, HbA1c by 0.55% (95% CI -0.84 to -0.27) and hs-CRP by 1.31 mg/L [3]. Across 18 RCTs (1,023 participants) with diabetes, gestational diabetes or prediabetes, zinc lowered serum insulin (MD -2.50, 95% CI -4.69 to -0.31) and HOMA-IR (MD -1.10, 95% CI -2.05 to -0.15), and LDL cholesterol rose slightly (MD 3.46, 95% CI 1.48 to 5.43) [4].
Population
People with and without diabetes [3]; people with diabetes or prediabetes [4].
Sources
[3], [4]
Caveats
The fasting glucose effect depended on diabetes status and on the zinc formulation [3].
Moderate

Wound healing

Shown to improve ulcer healing in 5 trials of people with ulcers, from moderate-quality evidence.

The numbers and sources
Effect
Across 5 clinical trials, zinc treatment was associated with better ulcer healing at the final endpoint (MD 1.41, 95% CI 1.04 to 1.92), from moderate-quality evidence [5].
Population
People with ulcers in 5 clinical trials [5].
Sources
[5]
Caveats
Only 5 trials. The abstract does not give the number of participants, the zinc route or the dose [5]. The abstract of [5] labels its pooled figure a mean difference (MD), though it reads like a ratio. It is given here as printed.
Moderate

Taste disorders

Shown to improve taste more often than control in adults with taste disorders, and to lower taste loss during head and neck radiation.

The numbers and sources
Effect
Across 12 RCTs (938 participants) with idiopathic or zinc-deficiency taste disorders, taste improved more often on zinc than on control (RR 1.38, 95% CI 1.16 to 1.64) [6]. In 3 trials in people receiving radiation for head and neck cancer, zinc lowered the incidence of taste loss (RR 0.72, 95% CI 0.67 to 0.92) and did not speed recovery of taste (RR 2.58, 95% CI 0.97 to 6.88) [7].
Population
Adults with taste disorders, including people with chronic kidney disease [6]; head and neck cancer patients during radiation therapy [7].
Sources
[6], [7]
Caveats
The two reviews studied different groups. The radiation review rests on 3 trials [7]. The interval for the radiation result (0.67 to 0.92 around 0.72) is as the abstract of [7] prints it.
ModerateStudied in women

Period pain

Shown in one meta-analysis of 6 trials to lower period pain more than placebo, with larger effects at 8 weeks or longer.

Compared with placebo [18]; placebo or no treatment [19]

The numbers and sources
Effect
Across 6 RCTs, zinc lowered pain severity more than placebo (Hedges's g -1.541, 95% CI -2.268 to -0.814). Longer treatment (8 weeks or more) gave larger reductions (p = 0.003), and higher doses added a small amount per milligram. Adverse events did not differ significantly from placebo (OR 2.54, 95% CI 0.78 to 8.26) [18]. In a Cochrane review, zinc sulfate lowered pain by 0.95 points on a 0 to 10 scale against placebo in one trial (95% CI 0.36 to 1.54, 99 women) [19].
Population
6 RCTs with 739 women with primary dysmenorrhea [18]; one RCT of 99 women within a review of 27 RCTs [19].
Sources
[18], [19]
Caveats
The Cochrane review rated its evidence low or very low quality [19]. The effect size in [18] is a standardized difference, not points on a pain scale.
StrongStudied in women

PMS symptoms

Shown in two reviews to ease PMS symptoms more than placebo, with small to moderate drops in total, emotional and physical symptom scores.

Compared with placebo [20][21]; placebo across the zinc trials reviewed [22]

The numbers and sources
Effect
Across 4 pooled RCTs, zinc lowered total PMS scores (Hedges's g -0.384) and emotional symptoms (g -0.347) with moderate certainty, and physical symptoms (g -0.512) with low certainty [20]. A second review of 5 studies found better physical health (MD 3.69, 95% CI 1.65 to 5.74) and fewer physical symptoms (MD -0.79, 95% CI -1.39 to -0.20) than placebo, with lower anger, anxiety and tearfulness scores [21]. A narrative review of 31 RCTs found zinc consistently improved psychological PMS symptoms, at 30 mg a day in 60 students and 50 mg a day in 142 women for 3 months [22].
Population
5 RCTs in women of reproductive age, 4 pooled [20]; 5 studies in young women with PMS [21]; 31 RCTs with 3,254 women aged 15 to 50 [22].
Sources
[20], [21], [22]
Caveats
All trials had some concerns for risk of bias, and the trials were few [20]. The two meta-analyses draw on largely the same small set of trials.

Mixed results2

Limited

Testosterone

Limited evidence: one small trial found no testosterone change in zinc-sufficient men, while a review, mostly of animal studies, found supplementation raised it, varying with baseline zinc.

The numbers and sources
Effect
In 14 exercising men with zinc-sufficient diets (11.9 to 23.2 mg a day), a zinc-magnesium supplement (ZMA) raised serum zinc but did not change serum total or free testosterone [9]. A systematic review of 8 clinical and 30 animal studies concluded zinc deficiency lowers testosterone and supplementation raises it, varying with baseline zinc and testosterone [10].
Population
14 young men [9]; mixed human and animal studies [10].
Sources
[9], [10]
Caveats
The sources point in different directions. The review [10] reports no pooled effect size and draws mostly on animal data.
Limited

Infections other than colds

Limited evidence: one trial found fewer infections in children with sickle cell anemia, while another found no change in deaths in infants with sepsis.

The numbers and sources
Effect
In children with sickle cell anemia, 20 mg zinc sulfate a day for 6 months led to 80 infections against 124 on placebo (305.7 against 480.7 per 100 person-years, IRR 0.62, 95% CI 0.45 to 0.86) [11]. In infants hospitalized with suspected sepsis, 10 mg a day for 14 days with antibiotics did not change death in hospital (4.1% against 4.9%, RR 0.83, 95% CI 0.60 to 1.15) or by 12 weeks (9.0% against 8.6%, RR 1.05, 95% CI 0.84 to 1.32) [12]. In adults hospitalized with COVID-19, ICU admission or death occurred in 5.7% on 90 mg zinc acetate a day and 23.5% on standard care alone (OR 0.21, 95% CI 0.03 to 0.96) [13].
Population
100 children aged 1 to 4 in Uganda, all on hydroxyurea [11]; 3,153 infants aged 3 to 59 days in India and Nepal [12]; 71 adults in one Spanish hospital [13].
Sources
[11], [12], [13]
Caveats
Each result comes from one trial in a different population. The sepsis trial was underpowered because events were fewer than expected, and vomiting was slightly more common on zinc [12]. The COVID-19 trial was small and open-label [13].

Not shown to help2

Moderate

Catching a cold, zinc taken daily

Not shown to prevent colds in children and adults taking zinc daily.

The numbers and sources
Effect
Zinc made little or no difference to the risk of developing a cold (RR 0.93, 95% CI 0.85 to 1.01, 9 studies, 1,449 participants, low certainty). When colds occurred, their length did not differ (MD -0.63 days, 95% CI -1.29 to 0.04, moderate certainty) [1].
Population
15 prevention trials in children and adults [1].
Sources
[1]
Caveats
Trials mixed common cold and upper respiratory infection definitions.
Moderate

Smell loss

Not shown to improve smell in adults with smell disorders, though one study reported improvement after head injury.

The numbers and sources
Effect
Across 6 studies, improvement in tested smell function did not differ between zinc and control (OR 1.78, 95% CI 0.63 to 5.03), nor did self-reported improvement (OR 0.69, 95% CI 0.25 to 1.93). One study reported improvement in people with smell loss after head injury [8].
Population
Adults with smell disorders in 3 RCTs and 3 observational studies of 25 to 606 participants, followed 1 to 15 months [8].
Sources
[8]
Caveats
Half the studies were observational. This concerns oral zinc. Intranasal zinc has been linked to smell loss (see Risks).

Doses studied

Cold treatment lozenges gave 45 to 276 mg a day of zinc gluconate for 4.5 to 21 days [1]. The lozenge meta-analysis compared 80 to 92 mg and 192 to 207 mg a day [2]. The taste disorder trials used 17 to 86.7 mg of elemental zinc a day for 3 to 6 months [6]. The ZMA trial used a commercial zinc and magnesium product in men already eating 11.9 to 23.2 mg a day [9]. The sickle cell trial gave 20 mg zinc sulfate a day [11], and the infant sepsis trial 10 mg a day for 14 days [12].

Risks

Reported risks3

ModerateHow often is not known

Nausea, taste disturbance and other minor effects

Shown to raise minor side effects such as unpleasant taste and nausea about 34% when used to treat colds.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
When zinc was used to treat colds, non-serious adverse events rose (RR 1.34, 95% CI 1.15 to 1.55, 16 studies, 2,084 participants, moderate certainty). Adverse events tracked in the trials included unpleasant taste, vomiting, stomach cramps and diarrhea. Prevention trials showed RR 1.11 (95% CI 0.84 to 1.47) for adverse events and 1.67 (95% CI 0.78 to 3.57) for serious adverse events [1].
Population
31 trials reporting non-serious adverse events, 2,422 participants [1].
Sources
[1]
Caveats
No treatment trial reported serious adverse events [1].
LimitedHow often is not known

Copper deficiency from excess zinc

Case reports: excess zinc led to copper deficiency with anemia and nerve damage, with blood counts usually recovering after zinc was stopped.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Three men developed zinc-induced copper deficiency, recognized on bone marrow examination: anemia and severe neutropenia, with progressive peripheral neuropathy in two [14]. A review of 37 published cases found elemental zinc doses from about 50 mg to more than 1,500 mg a day for weeks to years, from supplements, denture adhesive creams and swallowed coins. Anemia was present in nearly all cases, most often with neutropenia, and serum copper was low in every case. Blood counts recovered in most within weeks to months after zinc was stopped and copper given, while nerve damage improved more slowly and sometimes incompletely [15].
Population
Three case reports, including one man on prescribed zinc for acrodermatitis enteropathica [14]; 37 cases in 34 publications from 1972 to 2025 [15].
Sources
[14], [15]
Caveats
Case reports cannot give a rate. Bone marrow findings often led to an initial misdiagnosis of myelodysplastic syndrome [15].
LimitedHow often is not known

Loss of smell from intranasal zinc

Case reports: people lost their sense of smell after intranasal zinc gel. FDA states it received over 130 such reports by 2009.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
All 17 patients presenting with smell loss after intranasal zinc gluconate gel had impaired olfaction on testing. They reported deep sniffing, immediate burning, and smell loss within 48 hours. Seven never developed cold symptoms [16]. The FDA states it had received more than 130 reports of anosmia linked to Zicam intranasal zinc products by 2009 [17].
Population
Retrospective clinic case series [16]; FDA adverse event reports [17].
Sources
[16], [17]
Caveats
This concerns nasal gel and swabs, not oral zinc.

Claims tested and not found

  1. That daily zinc prevents colds. Risk of a cold did not differ from placebo (RR 0.93, 95% CI 0.85 to 1.01) [1].
  2. That zinc raises testosterone in men who already get enough. Serum total and free testosterone did not change on ZMA [9].
  3. That oral zinc restores lost smell. Tested smell function did not improve more than control across 6 studies (OR 1.78, 95% CI 0.63 to 5.03) [8].

Sources

  1. Nault D, Machingo TA, Shipper AG, et al. Zinc for prevention and treatment of the common cold. Cochrane Database of Systematic Reviews. 2024. https://doi.org/10.1002/14651858.CD014914.pub2
  2. Hemilä H. Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. JRSM Open. 2017. https://doi.org/10.1177/2054270417694291
  3. Wang X, Wu W, Zheng W, et al. Zinc supplementation improves glycemic control for diabetes prevention and management: a systematic review and meta-analysis of randomized controlled trials. American Journal of Clinical Nutrition. 2019. https://doi.org/10.1093/ajcn/nqz041
  4. Loaiza-Giraldo JP, Amigo-Fierro F, Cancino-Castro CI, et al. Effects of Zinc Supplementation on Glycemic Control, Insulin Resistance, Inflammation and Oxidative Stress in Diabetes: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Endocrinology, Diabetes & Metabolism. 2026. https://doi.org/10.1002/edm2.70264
  5. Arribas Lopez E, Zand N, Ojo O, Kochhar T. Systematic review and meta-analysis of the effect of zinc on wound healing. BMJ Nutrition, Prevention & Health. 2025. https://doi.org/10.1136/bmjnph-2024-000952
  6. Mozaffar B, Ardavani A, Muzafar H, Idris I. The Effectiveness of Zinc Supplementation in Taste Disorder Treatment: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Journal of Nutrition and Metabolism. 2023. https://doi.org/10.1155/2023/6711071
  7. Chi WJ, Myers JN, Frank SJ, et al. The effects of zinc on radiation-induced dysgeusia: a systematic review and meta-analysis. Supportive Care in Cancer. 2020. https://doi.org/10.1007/s00520-020-05578-8
  8. Fornazieri MA, Fornazieri HB, Artero NA, et al. The effects of zinc supplementation on olfactory disorders: a systematic review with meta-analysis. Brazilian Journal of Otorhinolaryngology. 2026. https://pubmed.ncbi.nlm.nih.gov/42950529/
  9. Koehler K, Parr MK, Geyer H, et al. Serum testosterone and urinary excretion of steroid hormone metabolites after administration of a high-dose zinc supplement. European Journal of Clinical Nutrition. 2009. https://doi.org/10.1038/sj.ejcn.1602899
  10. Te L, Liu J, Ma J, et al. Correlation between serum zinc and testosterone: A systematic review. Journal of Trace Elements in Medicine and Biology. 2023. https://doi.org/10.1016/j.jtemb.2022.127124
  11. Namazzi R, Mellencamp KA, Bagala I, et al. Daily Zinc Supplementation for Infection Prevention in Children With Sickle Cell Anemia: The ZIPS-2 Randomized Clinical Trial. JAMA. 2026. https://doi.org/10.1001/jama.2026.14190
  12. Wadhwa N, Sinha A, Basnet S, et al. Zinc as adjunct treatment for clinical severe infection in young infants: A randomized double-blind placebo-controlled trial in India and Nepal. PLOS Medicine. 2025. https://doi.org/10.1371/journal.pmed.1004759
  13. Gómez-Zorrilla S, Sendra E, Du J, et al. Zinc adjuvant treatment in SARS-CoV-2: A randomized clinical trial. Journal of Trace Elements in Medicine and Biology. 2025. https://doi.org/10.1016/j.jtemb.2025.127778
  14. Willis MS, Monaghan SA, Miller ML, et al. Zinc-induced copper deficiency: a report of three cases initially recognized on bone marrow examination. American Journal of Clinical Pathology. 2005. https://doi.org/10.1309/V6GVYW2QTYD5C5PJ
  15. Dutta A, Chaudhary V, Kumari S, et al. Zinc-Induced Hematologic Toxicities: A Systematic Review of Descriptive Studies. Biological Trace Element Research. 2026. https://doi.org/10.1007/s12011-026-05136-z
  16. Alexander TH, Davidson TM. Intranasal zinc and anosmia: the zinc-induced anosmia syndrome. Laryngoscope. 2006. https://doi.org/10.1097/01.mlg.0000191549.17796.13
  17. U.S. Food and Drug Administration. Homeopathic Drug Products: Guidance for FDA Staff and Industry. 2022. https://www.fda.gov/media/163755/download
  18. Hsu TJ, Hsieh RH, Huang CH, et al. Efficacy of Zinc Supplementation in the Management of Primary Dysmenorrhea: A Systematic Review and Meta-Analysis. Nutrients. 2024. https://doi.org/10.3390/nu16234116
  19. Pattanittum P, Kunyanone N, Brown J, et al. Dietary supplements for dysmenorrhoea. Cochrane Database of Systematic Reviews. 2016. https://doi.org/10.1002/14651858.cd002124.pub2
  20. Kim YM, Baek J. Effect of zinc supplementation on premenstrual symptoms: A systematic review and meta-analysis. Women & Health. 2025. https://doi.org/10.1080/03630242.2025.2539815
  21. Haider S, Sajjad M, Zahid M. A systematic review and meta-analysis examining the role of zinc supplementation in ameliorating physical and psychological manifestations of premenstrual syndrome in young females. European Journal of Obstetrics, Gynecology and Reproductive Biology. 2025. https://doi.org/10.1016/j.ejogrb.2025.114082
  22. Robinson J, Ferreira A, Iacovou M, Kellow NJ. Effect of nutritional interventions on the psychological symptoms of premenstrual syndrome in women of reproductive age: a systematic review of randomized controlled trials. Nutrition Reviews. 2025. https://doi.org/10.1093/nutrit/nuae043

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