Does Zinc Help With Colds? What 34 Trials Found About Lozenges

Zinc may make a cold a little shorter once it has started, and it has not been shown to stop you catching one. The 2024 Cochrane review of 34 trials in 8,526 people found that zinc "may have little or no effect on the prevention of colds but may reduce the duration of ongoing colds", by about 2.4 days, at low certainty and with more side effects such as an unpleasant taste and stomach upset.¹ Zinc gluconate in those trials was given at 45 to 276 mg a day. The NHS puts the zinc an adult needs at 9.5 mg a day for men aged 19 to 64 and 7 mg a day for women, and says of supplements: "Do not take more than 25mg of zinc supplements a day unless advised to by a doctor."²

What does zinc do for the immune system?

Zinc contributes to the normal function of the immune system.² That is the register wording authorised for zinc in Great Britain; no cold wording is authorised. Getting ill more often is one of the signs of zinc deficiency. In one small trial, 50 adults aged 55 to 87 on 45 mg a day for a year recorded fewer infections than the placebo group; the dose is above the NHS supplement line, and the group began with lower plasma zinc than younger adults.³ The Wellgard zinc guide covers the rest; the vitamins and minerals guide sets it among the other nutrients.

Does zinc prevent colds?

Not in the trials so far. Across nine prevention studies with 1,449 participants, people taking zinc were about as likely to catch a cold as people taking a placebo (risk ratio 0.93, 95% confidence interval 0.85 to 1.01), a low-certainty result the reviewers summarised as "little or no reduction in the risk of developing a cold".¹ When they did catch one, it lasted about as long: 0.63 days shorter, not significant.¹ A daily supplement closes a dietary gap; keeping colds away is a purpose the trials have not shown.

How many days does zinc shorten a cold?

About two and a half on the Cochrane average. Eight treatment trials with 972 participants gave a mean difference of 2.37 days (0.53 to 4.21 days shorter), at low certainty, and the trials disagreed widely (I² 97%).¹ A 2011 analysis of 13 lozenge comparisons found that the five trials using under 75 mg of zinc a day "uniformly found no effect", while trials above 75 mg a day reported colds 20% to 42% shorter;⁴ a 2017 meta-analysis of seven trials above 75 mg a day (575 people) put the average at 33% shorter, with no extra effect at 192 to 207 mg.⁵ The most recent trial points the other way: 87 Finnish adults on 13 mg zinc acetate lozenges six times a day (78 mg) for five days recovered no faster than the placebo group (rate ratio 0.68, 0.42 to 1.08).⁶

What were the lozenge trials actually like?

Short and high-dose. Half the trials (17 of 34) used lozenges, mostly zinc gluconate or zinc acetate dissolved slowly in the mouth from the first symptoms; gluconate was given at 45 to 276 mg a day for 4.5 to 21 days.¹ Acetate and gluconate did not differ significantly (40% against 28% shorter).⁵

The trial doses are three times the NHS supplement line and more, and the NHS gives its reason for the line: "Taking high doses of zinc reduces the amount of copper the body can absorb. This can lead to anaemia and weakening of the bones."² This describes trial conditions, not a regimen. A lozenge's zinc counts towards the day's total along with every other product carrying zinc, so a lozenge on top of a multivitamin can pass 25 mg quickly: add the labels up (how much zinc a day and can you take too much zinc set out the line), and ask a pharmacist or GP before any high-dose course.

Why do some pages still quote a 2013 review?

Because the earlier Cochrane review on zinc for the common cold, published in 2013, was widely reported and then withdrawn in 2015, and many pages written in between were never updated.⁷ A figure of "a day shorter" with no date on it may trace back to it. The 2024 review replaced it.

Did zinc help in COVID-19 trials?

Not in the two randomised trials: 50 mg zinc gluconate a day for ten days made no significant difference to symptom duration in 214 outpatients, and the trial stopped early for futility;⁸ 40 mg a day for eight weeks had no effect on time to symptom resolution in 181 adults in India (hazard ratio 0.94, 0.67 to 1.33).⁹ Neither dose is within UK supplement guidance.

What are the side effects of zinc lozenges?

An unpleasant taste, stomach cramps and vomiting were the events the review counted. Across 16 treatment trials with 2,084 participants, non-serious side effects were more likely with zinc than with placebo (risk ratio 1.34, 1.15 to 1.55, moderate certainty);¹ in the Finnish trial, 63% of the zinc group reported adverse effects against 31% on placebo.⁶ The UK Expert Group on Vitamins and Minerals found nausea and cramps from zinc supplements "particularly apparent when the supplements were taken with little or no food", so zinc is usually taken with a meal.¹⁵ Zinc applied inside the nose is a separate matter: a clinic series described 17 people who lost their sense of smell within 48 hours of using an intranasal zinc gluconate gel sold for colds, after a burning sensation on application,¹⁰ and a later analysis of 25 such patients concluded that intranasal zinc gluconate causes loss of smell.¹¹ Avoid zinc nasal sprays and gels.

Is zinc or vitamin C better for a cold?

Neither prevents colds in the general population. Regular vitamin C did not reduce the number of colds in community trials of 10,708 people (risk ratio 0.97, 0.94 to 1.00) and shortened them by 8% in adults and 14% in children; starting it once a cold had begun showed no consistent effect.¹² Zinc's is the reverse: nothing on prevention, a possible effect on duration. Both contribute to the normal function of the immune system. Can you take vitamin C and zinc together covers the pairing, and what is vitamin C good for the vitamin alone.

When should you see a GP about a cold?

The NHS says: "You can often treat a cold without seeing a GP. You should begin to feel better in about 1 to 2 weeks." It notes: "There's little evidence that supplements such as vitamin C, echinacea or garlic prevent colds or help you get better more quickly." Its see-a-GP list: "you have a high temperature for more than 3 days", "your cold symptoms get worse", "your temperature is very high, or you feel hot, cold or shivery", "you feel short of breath or have chest pain", "you're worried about your child's cold symptoms", "your cold symptoms do not get better after 10 days", "you have a cough for more than 3 weeks", and cold symptoms alongside a long-term medical condition or a weakened immune system.¹³ Call 111 if you're not sure what to do, and 999 for severe difficulty breathing.

Frequently asked questions

What is the best form of zinc for a cold?

In the lozenge trials above 75 mg a day, zinc acetate and zinc gluconate did not differ significantly (40% against 28% shorter colds); the effect, where it appeared, came from a high-dose lozenge dissolving slowly in the mouth rather than from the salt.⁵ Which type of zinc is best covers everyday forms.

Is it normal to feel sick after taking zinc?

Feeling sick is a known effect of zinc at high doses, more so on an empty stomach.¹⁵ Take zinc with a meal and keep to the label dose; vomiting, cramps or a metallic taste after a high dose are reasons to stop and speak to a pharmacist.

Can zinc calm a bacterial infection?

No. The trials here are in viral colds, and zinc has no evidence and no authorised wording for bacterial illness; a suspected bacterial infection needs a GP. If you are prescribed an antibiotic, tell the pharmacist about any zinc you take: for ciprofloxacin the NHS says "Leave 2 hours in between taking supplements and your dose of ciprofloxacin tablets or liquid", and it lists "medicines or supplements that contain iron or zinc" among those that "may not mix well" with doxycycline.¹⁴ What should you not take with zinc covers spacing.

Sources

1. Nault D, et al. Zinc for prevention and treatment of the common cold. Cochrane Database Syst Rev, 2024. PubMed 38719213.
2. NHS. Vitamins and minerals: others. nhs.uk; Great Britain nutrition and health claims register. gov.uk.
3. Prasad AS, et al. Zinc supplementation decreases incidence of infections in the elderly. Am J Clin Nutr, 2007. PubMed 17344507.
4. Hemilä H. Zinc lozenges may shorten the duration of colds: a systematic review. Open Respir Med J, 2011. PubMed 21769305.
5. Hemilä H. Zinc lozenges and the common cold: zinc acetate against zinc gluconate, and dosage. JRSM Open, 2017. PubMed 28515951.
6. Hemilä H, et al. Zinc acetate lozenges for the treatment of the common cold: a randomised controlled trial. BMJ Open, 2020. PubMed 31980506.
7. Singh M, Das RR. Zinc for the common cold. Cochrane Database Syst Rev, 2013, PubMed 23775705; withdrawn 2015, PubMed 25924708.
8. Thomas S, et al. High-dose zinc and ascorbic acid vs usual care in ambulatory patients with SARS-CoV-2 infection. JAMA Netw Open, 2021. PubMed 33576820.
9. Partap U, et al. Vitamin D and zinc supplementation among COVID-19 patients in India: a double-blind randomised trial. Curr Dev Nutr, 2023. PubMed 37560461.
10. Alexander TH, Davidson TM. Intranasal zinc and anosmia: the zinc-induced anosmia syndrome. Laryngoscope, 2006. PubMed 16467707.
11. Davidson TM, Smith WM. The Bradford Hill criteria and zinc-induced anosmia. Arch Otolaryngol Head Neck Surg, 2010. PubMed 20644061.
12. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev, 2013. PubMed 23440782.
13. NHS. Common cold. nhs.uk.
14. NHS. Ciprofloxacin with other medicines and supplements, nhs.uk; doxycycline with other medicines and supplements, nhs.uk.
15. Expert Group on Vitamins and Minerals. Safe Upper Levels for Vitamins and Minerals, 2003: zinc. UK Government Web Archive.

This article is general information, not medical advice; do not take zinc above 25 mg a day without medical advice.