Could this supplement help you shake off a cold sooner? The evidence is “promising”, says this registered dietitian

If participants in my exercise classes are anything to go by then cold season is already upon us. Many are nursing sore throats, coughs and congestion that barely clear before symptoms return. This led me to research whether anything could help a cold end sooner.

While there is currently no cure for the common cold, registered dietitian Johannah Katz RD says studies indicate that zinc could shorten a cold, potentially by two days.

“Zinc is interesting because the evidence suggests it may be more useful once a cold starts than as a general immune supplement,” says Katz. “A 2024 Cochrane review found it may shorten symptoms by around two days, although the evidence isn't conclusive.”

She says the strongest evidence supports starting zinc very early, “ideally within 24 hours of the first symptoms.”

What is zinc and how might it shorten a cold?

Zinc is a mineral that the immune system needs to work properly.

Think of your immune cells as a team defending your body—zinc helps them work properly, communicate and respond to germs. It also helps regulate inflammation (the body’s response to infection) so that it doesn’t become excessive.

“The certainty of that [Cochrane review] evidence was rated low because the studies varied substantially in dose, formulation and design.

“I’d describe the research as promising rather than definitive. The same review did not find convincing evidence that zinc meaningfully reduces overall symptom severity.”

A 2027 meta-analysis of seven trials found that zinc lozenges containing more than 75mg of zinc, shortened colds by an average of 33% compared with placebo. Zinc lozenges dissolve slowly, releasing zinc around your mouth and throat.

Researchers suggested that zinc might make it harder for cold viruses to spread and make copies of themselves. Releasing the zinc locally in the mouth and throat may also be a contributing factor, although scientists haven’t confirmed this.

Katz agrees there is “better evidence” for zinc lozenges than a swallowed tablet.

“Both zinc acetate and zinc gluconate lozenges have shown benefit, and a meta-analysis did not find a significant difference between the two.

“I’d look at the amount of elemental zinc [actual weight of zinc mineral] rather than the total weight of the zinc compound [with its carrier elements].

“Intranasal zinc sprays or gels should be avoided because they have been linked with potentially permanent loss of smell.”

What doses have researchers studied and are they safe?

“Trials showing benefits have commonly used roughly 75-90 mg of elemental zinc per day, often around 80-92 mg/day, for the duration of the cold and generally for less than two weeks,” says Katz.

“There’s no evidence that going above about 100 mg/day works better. However, these amounts exceed the usual adult tolerable upper intake level of 40 mg/day, so I wouldn’t recommend routinely self-supplementing at those doses without checking with a pharmacist or healthcare professional.”

This is the US adult upper limit, covering zinc from food and supplements. NHS guidance advises taking no more than 25mg of zinc supplements daily unless advised by a doctor.

Zinc also comes with some side effects, says Katz. “The most common problems are nausea, stomach upset and an unpleasant or metallic taste. Long-term high-dose zinc can interfere with copper absorption and can actually impair immune function.

“Zinc can also interact with tetracycline and quinolone antibiotics and with penicillamine, so anyone taking medications should check with their pharmacist.”

Katz points out that taking zinc as a preventative measure is probably not worth it. “The latest Cochrane review found that preventive zinc supplementation may have little or no effect on the likelihood of developing a cold,” she says. “Its potential usefulness appears stronger as a short-term intervention started once symptoms begin.”

While zinc isn’t guaranteed to stop a cold in its tracks, Katz’s advice is to weigh the possible benefit against the risks. “The evidence suggests that the right formulation, started early, may modestly shorten how long someone is sick and that potential benefit has to be weighed against the dose and side effects,” she says.