- Treating a cold: zinc started early may shorten a cold by about 2 days on average. A 2024 Cochrane review rated this low-certainty evidence.
- Preventing colds: daily zinc made little or no difference to whether people caught a cold (Grade D for prevention).
- Zinc deficiency: correcting a true deficiency matters, especially in older adults. That is a different question from “boosting” a normal immune system.
- Safety: nausea and a bad taste are common. Never use zinc nasal sprays or gels. Long-term high doses can cause copper deficiency.
Last reviewed: 5 October 2026 · Written by SD, pharmacist · No products were supplied and no commission is earned from this review.
The short answer
Zinc is one of the few cold remedies with a real body of randomised trials. The results are more mixed than “take zinc at the first sniffle” suggests. Across trials, people who started zinc soon after symptoms began got better roughly two days sooner on average. But the trials vary hugely in dose, form and quality, so the size of that benefit is uncertain. Taking zinc every day to avoid catching colds does not appear to work in people who aren’t deficient.
The trade-off is side effects. Zinc lozenges commonly cause a bad taste and nausea, and about 1 extra person in 7 has a side effect compared with placebo. If you try zinc, do it as a short course of lozenges started early, not as a long-term “immune booster”.
How might it work?
- A local effect in the throat. The leading theory is that zinc ions released from a lozenge act locally in the throat and nose. In laboratory studies, zinc ions interfere with rhinoviruses (the main cause of colds) and with inflammation in the airway lining. This is why most positive trials used lozenges dissolved slowly in the mouth, not swallowed tablets.
- Immune function. Zinc is essential for many immune cells. People who are deficient have weaker immune responses, and correcting the deficiency helps. That does not mean extra zinc pushes a normal immune system above normal.
The local mechanism explains why the form matters. Some lozenges contain ingredients such as citric acid that bind zinc, so they may release little free zinc in the mouth. This is one suggested reason why some trials found nothing.[4]
What the human trials show
Treating a cold that has already started
| Review | What was pooled | Main finding | Certainty |
|---|---|---|---|
| Cochrane, Nault 2024[1] | 8 treatment trials, 972 people. All zinc forms (lozenges, syrups, tablets, nasal). | Colds about 2.4 days shorter (95% CI 0.5 to 4.2 days). No clear effect on symptom severity. | Low |
| Hunter 2021, BMJ Open[2] | 28 RCTs in adults with viral respiratory infections. | Symptoms resolved about 2 days earlier with zinc lozenges or nasal zinc. Day 7: 19 more people per 100 still had symptoms without zinc. | Very low to low |
| Hemilä 2017[3] | 7 lozenge trials, 575 people, zinc >75 mg/day. | Colds 33% shorter. Doses above 100 mg/day did not work better. | Not GRADE-rated |
| Hemilä 2016, individual patient data[5] | 3 zinc acetate lozenge trials, 199 people. | Colds about 2.7 days shorter, against a 7-day average cold. | Not GRADE-rated |
Pharmacist’s take: the direction of the evidence is consistent: zinc started early seems to shorten colds. But the Cochrane analysis shows very high heterogeneity between trials (I² = 97%). In other words, individual trials gave very different answers, from no effect to large effects. Some researchers argue that pooling weak formulations with well-designed high-dose acetate lozenges hides a real effect.[4] Others say the overall evidence simply isn’t strong enough yet. Both views are reasonable. Our grade reflects that uncertainty.
Preventing colds
The Cochrane review pooled 9 prevention trials with 1,449 people. Daily zinc made little or no difference to the risk of catching a cold (risk ratio 0.93, 95% CI 0.85 to 1.01; low certainty). When colds did occur, they were probably not meaningfully shorter (about 0.6 days, not statistically significant; moderate certainty).[1] The BMJ Open review was slightly more positive, estimating around 5 fewer infections per 100 person-months.[2] The trials it included vary in population and quality.
When zinc clearly matters: deficiency
In nursing-home residents, those with low blood zinc had more pneumonia and used more antibiotics than those with normal levels.[6] This was an observational study, so it can’t prove that zinc prevents pneumonia. A 2026 randomised trial in zinc-deficient nursing-home residents found that 60 mg a day reliably corrected deficiency over several months, while 30 mg a day often did not.[7] That trial was not designed to show fewer infections. We covered it in our Evidence Update of 2 October 2026. Deficiency should be identified and treated under medical supervision, not guessed at with high-dose supplements.
Lozenges, tablets or sprays: does the form matter?
| Form | Approx. elemental zinc | Evidence for colds | Notes |
|---|---|---|---|
| Zinc acetate lozenges | ~30% | Most consistent positive trials[3][5] | Releases zinc ions readily in the mouth |
| Zinc gluconate lozenges | ~14% | Mixed; well-formulated ones may work about as well[3] | Most studied form; formulation matters |
| Swallowed tablets/capsules (sulfate, citrate, picolinate) | ~20–30% | Little direct evidence for treating colds | Suitable for correcting deficiency |
| Zinc oxide | ~80% | Little evidence | Poorly suited to lozenges |
| Nasal sprays / gels | — | Some trials, but… | Avoid: linked to permanent loss of smell[8] |
Label trap: labels may show the weight of the zinc compound rather than the zinc itself. For example, “50 mg zinc gluconate” contains only about 7 mg of elemental zinc. Always look for the elemental zinc figure.
Safety and interactions: a pharmacist’s checklist
- Daily needs: Australian adults need about 14 mg a day (men) and 8 mg a day (women). The upper limit for long-term intake is 40 mg a day.[9] Cold trials used higher doses, but only for days to two weeks.
- Common side effects: bad or metallic taste, nausea, and mouth irritation. These were more common with zinc than placebo (risk ratio about 1.3–1.4).[1][2] Taking zinc on an empty stomach makes nausea more likely.
- Copper deficiency: taking 50 mg a day or more for weeks to months can block copper absorption. Prolonged excess has caused anaemia, low white cell counts and nerve damage, which may not fully recover.[10][11] Watch for hidden zinc in multivitamins and in some denture adhesives.
- Loss of smell: zinc nasal gels and sprays have been linked to sudden, sometimes permanent, loss of smell.[8] Don’t use them.
- Pregnancy and breastfeeding: normal dietary-level intakes are fine. Avoid high-dose cold courses unless a doctor or pharmacist advises them.
| Medicine | Problem | What to do |
|---|---|---|
| Quinolone antibiotics (e.g. ciprofloxacin) Tetracycline antibiotics (e.g. doxycycline) | Zinc binds the antibiotic and reduces its absorption | Take the antibiotic at least 2 h before or 4–6 h after zinc[10] |
| Penicillamine | Reduced absorption of both | Separate by at least 1 h[10] |
| Thiazide diuretics (e.g. hydrochlorothiazide) | Increase zinc loss in urine | Long-term users may have lower zinc levels; ask your doctor[10] |
| Iron supplements (25 mg or more) | Can reduce zinc absorption | Take at different times of day[10] |
| Magnesium and calcium supplements | High doses compete with zinc for absorption | Space them apart if taking high doses. See our magnesium glycinate review for magnesium’s own interactions. |
Who might reasonably try it?
- Worth considering: healthy adults who want to shorten a cold, if they can tolerate the taste. Most positive trials used this approach:
- Zinc acetate or gluconate lozenges, dissolved slowly in the mouth.
- Started within 24 hours of symptoms.
- Roughly 75–100 mg of elemental zinc a day, split across lozenges every 2–3 hours while awake.
- Stopped when the cold resolves, and not taken for more than about a week or two.
- Probably not worth it:
- Taking zinc daily “for immunity” if you eat a varied diet. Zinc-rich foods include meat, seafood (especially oysters), dairy, legumes, nuts and wholegrains.
- Starting zinc several days into a cold.
- Talk to your doctor or pharmacist first if you:
- Take antibiotics, penicillamine or diuretics.
- Have a gut condition that affects absorption, or have had bariatric surgery.
- Are pregnant.
- Are buying zinc for a child.
- Have been taking zinc for months.
- See a doctor: if cold symptoms last more than 10 days or get worse. Also see a doctor for high fever, chest pain or shortness of breath.
How to judge a zinc lozenge
We don’t recommend specific brands. Instead, check any product against these criteria:
- Form: zinc acetate or zinc gluconate, made to dissolve in the mouth, not to be swallowed.
- Elemental zinc stated clearly per lozenge, typically around 10–15 mg.
- Few zinc-binding additives: avoid citric acid, tartaric acid and similar acids high on the ingredient list.
- No nasal zinc products of any kind.
- Independent testing: look for USP Verified, NSF or a published certificate of analysis. In Australia, check for an AUST L number on the pack.
- Check your total intake from multivitamins so you don’t exceed safe limits once the course is over.
Our evidence grade
| Claim | Grade | Why |
|---|---|---|
| Zinc lozenges shorten a cold if started early | C: limited but promising | Multiple RCTs and meta-analyses point the same way, but certainty is low and results are highly inconsistent |
| Daily zinc prevents colds (non-deficient people) | D: weak or inconsistent | The Cochrane review found little or no effect |
| Correcting diagnosed zinc deficiency | Standard medical care | Not a supplement claim: get tested and treat under supervision |
The cold-treatment grade could rise to B if large, well-designed trials of properly formulated lozenges confirm the benefit.
References
- Nault D, Machingo TA, Shipper AG, et al. Zinc for prevention and treatment of the common cold. Cochrane Database Syst Rev. 2024;5:CD014914. doi:10.1002/14651858.CD014914.pub2
- Hunter J, Arentz S, Goldenberg J, et al. Zinc for the prevention or treatment of acute viral respiratory tract infections in adults: a rapid systematic review and meta-analysis of randomised controlled trials. BMJ Open. 2021;11:e047474. doi:10.1136/bmjopen-2020-047474
- 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;8(5):2054270417694291. doi:10.1177/2054270417694291
- Hemilä H, Chalker E. Shortcomings in the Cochrane review on zinc for the common cold (2024). Front Med. 2024;11:1470004. doi:10.3389/fmed.2024.1470004
- Hemilä H, Petrus EJ, Fitzgerald JT, Prasad A. Zinc acetate lozenges for treating the common cold: an individual patient data meta-analysis. Br J Clin Pharmacol. 2016;82(5):1393–1398. doi:10.1111/bcp.13057
- Meydani SN, Barnett JB, Dallal GE, et al. Serum zinc and pneumonia in nursing home elderly. Am J Clin Nutr. 2007;86(4):1167–1173. doi:10.1093/ajcn/86.4.1167
- Zinc dose-comparison trial in zinc-deficient nursing-home residents. Front Nutr. 2026. doi:10.3389/fnut.2026.1935770
- Alexander TH, Davidson TM. Intranasal zinc and anosmia: the zinc-induced anosmia syndrome. Laryngoscope. 2006;116(2):217–220. doi:10.1097/01.mlg.0000191549.17796.13
- NHMRC. Nutrient Reference Values for Australia and New Zealand: Zinc. eatforhealth.gov.au
- NIH Office of Dietary Supplements. Zinc: fact sheet for health professionals. ods.od.nih.gov
- Greenberg SA, Briemberg HR. A neurological and hematological syndrome associated with zinc excess and copper deficiency. J Neurol. 2004;251(1):111–114. doi:10.1007/s00415-004-0263-0
This article is general educational information, not personal medical advice. Talk to your doctor or pharmacist before starting a supplement, especially if you take regular medicines, are pregnant or breastfeeding, or are buying for a child. Evidence for Supplements does not accept payment or free products from supplement manufacturers for reviews.