Asked on Healicus
Do zinc lozenges actually shorten a cold?
Answer published by a reader on . AI-generated from the sources below; general educational information, not medical advice.
Yes, probably by about 2 days — but the evidence is low-certainty and the side effects are real.
A 2024 Cochrane review of 34 randomised trials (8,526 people) found that zinc taken during a cold may shorten it by around 2.4 days on average 1Nault D et al., Zinc for prevention and treatment of the common cold, Cochrane Database Syst Rev 2024Source of the Zinc lozenges cardNault 2024 Cochrane review (34 RCTs, n=8,526): used as treatment, zinc may shorten a cold by about 2.4 days (mean difference -2.37 days; 8 trials, n=972; low-certainty evidence, I² 97%), with more non-serious adverse events (RR 1.34, moderate certainty) such as nausea and bad taste. For prevention, zinc may make little or no difference to the risk of catching a cold (low certainty). Forms and doses varied widely, so no single lozenge regimen is established.Open on pubmed.ncbi.nlm.nih.gov ↗. That's meaningful when you're miserable. The catch: results varied enormously between trials (different forms, different doses, different timing), so the "2 days" figure is a rough central estimate, not a reliable guarantee 1Nault D et al., Zinc for prevention and treatment of the common cold, Cochrane Database Syst Rev 2024Source of the Zinc lozenges cardNault 2024 Cochrane review (34 RCTs, n=8,526): used as treatment, zinc may shorten a cold by about 2.4 days (mean difference -2.37 days; 8 trials, n=972; low-certainty evidence, I² 97%), with more non-serious adverse events (RR 1.34, moderate certainty) such as nausea and bad taste. For prevention, zinc may make little or no difference to the risk of catching a cold (low certainty). Forms and doses varied widely, so no single lozenge regimen is established.Open on pubmed.ncbi.nlm.nih.gov ↗.
A few things worth knowing:
- Start early — trials dosed within 24 hours of the first symptom; waiting longer likely reduces any benefit 1Nault D et al., Zinc for prevention and treatment of the common cold, Cochrane Database Syst Rev 2024Source of the Zinc lozenges cardNault 2024 Cochrane review (34 RCTs, n=8,526): used as treatment, zinc may shorten a cold by about 2.4 days (mean difference -2.37 days; 8 trials, n=972; low-certainty evidence, I² 97%), with more non-serious adverse events (RR 1.34, moderate certainty) such as nausea and bad taste. For prevention, zinc may make little or no difference to the risk of catching a cold (low certainty). Forms and doses varied widely, so no single lozenge regimen is established.Open on pubmed.ncbi.nlm.nih.gov ↗
- Nausea and bad taste are common — zinc users had significantly more of these side effects 1Nault D et al., Zinc for prevention and treatment of the common cold, Cochrane Database Syst Rev 2024Source of the Zinc lozenges cardNault 2024 Cochrane review (34 RCTs, n=8,526): used as treatment, zinc may shorten a cold by about 2.4 days (mean difference -2.37 days; 8 trials, n=972; low-certainty evidence, I² 97%), with more non-serious adverse events (RR 1.34, moderate certainty) such as nausea and bad taste. For prevention, zinc may make little or no difference to the risk of catching a cold (low certainty). Forms and doses varied widely, so no single lozenge regimen is established.Open on pubmed.ncbi.nlm.nih.gov ↗
- It doesn't seem to prevent colds — for that purpose, zinc showed little or no effect 1Nault D et al., Zinc for prevention and treatment of the common cold, Cochrane Database Syst Rev 2024Source of the Zinc lozenges cardNault 2024 Cochrane review (34 RCTs, n=8,526): used as treatment, zinc may shorten a cold by about 2.4 days (mean difference -2.37 days; 8 trials, n=972; low-certainty evidence, I² 97%), with more non-serious adverse events (RR 1.34, moderate certainty) such as nausea and bad taste. For prevention, zinc may make little or no difference to the risk of catching a cold (low certainty). Forms and doses varied widely, so no single lozenge regimen is established.Open on pubmed.ncbi.nlm.nih.gov ↗
- Lozenge doses in trials (around 45–276 mg/day) are well above the EU's tolerable upper intake level of 25 mg/day, so these are short-course therapeutic doses, not something to take indefinitely
For comparison, regular vitamin C (200 mg/day year-round) has better-certainty evidence for modest cold shortening (~8% in adults), but also shows little effect when started after symptoms begin.
Bottom line: zinc lozenges are one of the better-studied natural options for cold duration, but "low certainty" means the effect could be smaller — or larger — than the average suggests.
Sources
In this answer
Have a follow-up, or a question of your own? Every answer cites Cochrane, EU regulators, guideline bodies or trials in leading journals.