Zinc bound to gluconic acid, supplying about 13% elemental zinc. It is the most common form in supplements and in cold lozenges, and one of the two salts used in most zinc-and-colds trials.
Zinc has one of the better-evidenced supplement stories and one of the most abused. Deficiency is genuine and consequential — it impairs immune function, wound healing, taste and growth, and zinc supplementation in children in low-income settings reduces diarrhoea duration and mortality, which is why WHO includes it in treatment protocols. For colds, lozenges taken within a day of symptom onset have shortened illness in meta-analyses, although a 2024 Cochrane update rated the certainty of that evidence low. Where it goes wrong is chronic high-dose use: 50 mg/day sustained for months causes copper deficiency, which can produce an irreversible spinal cord disorder, and intranasal zinc has caused permanent loss of smell.
Sold as
Tablet, Capsule, Lozenge, Syrup, Component of multivitamins and cold remedies
Also known as
Zinc, Gluconate zinc, Cold lozenge zinc
Regulation: The Tolerable Upper Intake Level is 40 mg/day of elemental zinc for adults, set on copper metabolism and impaired immune function. The FDA warned against intranasal zinc products after reports of permanent loss of smell, and several were withdrawn. Oral lozenges commonly supply 13–25 mg per lozenge, so a full-day lozenge regimen exceeds the upper limit substantially.
What the research used
The amounts, forms and durations published trials of Zinc gluconate actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Recommended Dietary Allowance, adults
8–11 mg
Strong
8 mg/day for women and 11 mg/day for men. Vegetarians may need substantially more because phytate in legumes and grains binds zinc and reduces absorption.
Studied for Tolerable Upper Intake Level, adults
40 mg
Strong
Set on copper metabolism. Note that cold-lozenge regimens deliberately exceed it for short periods, which is defensible for a few days and not for months.
Studied for Common cold lozenge trials
75–100 mg
Moderate
Lozenges dissolved in the mouth, divided through the day · Started within 24 hours of symptom onset, until symptoms resolve
Trials used zinc gluconate or acetate lozenges at these daily totals. Formulations containing citric acid, sorbitol or mannitol bind zinc and appear not to work, which explains some of the inconsistency between trials.
Studied for Childhood diarrhoea in low-income settings
10–20 mg
Strong
Daily, alongside oral rehydration · 10–14 days
A WHO-recommended protocol supported by multiple trials in populations where zinc deficiency is common.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
Each timing below was actually compared against an alternative in a trial, which is unusual.
⏳On an empty stomach
Moderate
Zinc absorption is higher without food, but taking it fasted commonly causes nausea, so many people take it with a meal and accept lower absorption. Phytate-rich meals reduce absorption substantially — this has been measured directly.
Timing was tested. A trial compared this window against another and reported a difference.
🕐Any time
Moderate
Zinc and copper compete for the same intestinal transport, and high zinc induces metallothionein which traps copper in intestinal cells. Separating zinc from copper-containing supplements is standard practice, though the interaction depends more on total zinc dose than on timing.
Timing was tested. A trial compared this window against another and reported a difference.
The evidence in depth
Best supported: Moderate
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
Zinc lozenges started within a day of symptom onset shortened common cold duration in meta-analyses, by roughly a couple of days in the more favourable analyses. A 2024 Cochrane update graded the certainty of this evidence as low, citing heterogeneous formulations and doses, so the effect is plausible but less settled than popular accounts suggest. Zinc for childhood diarrhoea in deficient populations is on much firmer ground.
What may be going on: Zinc ions inhibit rhinovirus replication and receptor binding in laboratory work, and zinc is required for the development and function of several immune cell lines.
Moderate evidence. Several human studies point the same way, with real caveats.
The AREDS formulation, which contained 80 mg of zinc with copper and antioxidants, slowed progression to advanced age-related macular degeneration in people with intermediate disease. That result belongs to the combination at a specific high dose in a specific population, not to zinc supplements generally.
Moderate evidence. Several human studies point the same way, with real caveats.
Oral zinc has been studied in acne, with meta-analyses reporting modest improvement in inflammatory lesion counts but less than standard treatments. Zinc deficiency also causes a characteristic rash that resolves on repletion.
Limited evidence. Early human work, or mostly lab and animal research.
Zinc is concentrated in prostate tissue, which is why it appears in most prostate formulas, but no trial has shown supplementation benefits prostate symptoms. A large cohort study found long-term supplemental zinc above 100 mg/day associated with a higher rate of advanced prostate cancer, which is a reason for restraint rather than enthusiasm. The related testosterone claim is equally unsupported in men with normal zinc status.
Not enough evidence. Not enough human research to say anything useful yet.
Deep research mode adds each paper’s own conclusion and stated limitations.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Too much
Copper deficiency and irreversible myelopathy with chronic high doses
Sustained zinc intake around 50 mg/day or above depletes copper, causing anaemia, low white cell counts and — in a well-documented pattern — a myelopathy resembling subacute combined degeneration, with numbness, weakness and unsteady walking that often does not fully resolve after stopping. Cases have followed both supplements and excessive use of zinc-containing denture adhesives. Long-term zinc above the upper limit should include copper, and ideally medical monitoring.
Too much
Intranasal zinc and permanent loss of smell
Zinc gels and swabs applied inside the nose have caused anosmia, in some cases permanent. The FDA warned consumers and products were withdrawn. Nothing about oral lozenges implies the nasal route is safe.
Interaction
Reduces absorption of antibiotics, and is reduced by several drugs
Zinc binds tetracyclines and fluoroquinolones in the gut and reduces penicillamine absorption; separation by two to four hours is standard. Thiazide diuretics increase urinary zinc loss, and long-term proton pump inhibitor use may reduce zinc absorption.
Too much
Nausea, metallic taste and gastrointestinal upset
Zinc on an empty stomach frequently causes nausea and vomiting, and lozenges commonly cause a persistent metallic taste and mouth irritation, which is the main reason people abandon the cold regimen.
Worth knowing
Total zinc adds up across products
Multivitamins, cold remedies, prostate formulas and immune blends all contain zinc. Taking several at once can quietly reach the copper-depleting range, and the products rarely warn about each other.
In the food catalogue
The whole-food form, where one exists. The evidence for a concentrated extract rarely transfers to the food, or the other way round — these are cross-links, not equivalents.