Zinc for Colds and Flu – and Covid 19

By Robert H. Shmerling, M.D., Harvard Health Publishing | January 13th, 2023

Sure, but does it work?

Hand holding pills. Over-the-counter zinc supplements could be one way to make cold and flu season a bit easier. What can we do to prevent and treat seasonal illnesses? We look at zinc for colds and flu and Covid. Does it really work?

Taking measures to prevent and treat seasonal illnesses can give us more agency over our health, but which measures really work? Dr. Robert H. Shmerling of Harvard Health Publishing looks at zinc for colds and flu and for Covid, examining whether it’s useful for prevention and treatment.


Does zinc really work for colds and flu?


This question is timely with cold and flu season upon us.

For many years, there’s been interest in the possibility that zinc, or other supplements, could help prevent or treat colds and flu. A recent analysis reviewed available research and suggested that over-the-counter zinc supplements could be one way to make cold and flu season a bit easier.

Published in November 2021 in BMJ Open, the study looks at zinc for preventing or treating colds and flu-like illness. Researchers reviewed more than 1,300 studies and narrowed the analysis down to 28 well-designed trials, which included more than 5,000 study subjects. Here’s what they found.

For preventing colds and flu-like illness:

  • Zinc therapy was associated with fewer upper respiratory infections compared with placebo. The effect was modest: about one infection was prevented for every 20 people using zinc. The strength of the evidence was considered low.
  • A few studies suggest preventive effects were largest for reducing severe symptoms, such as high fever.
  • Small studies of intentional exposure to a cold virus found that zinc did not prevent colds.

For treating colds and flu-like illness:

  • Those who took zinc had symptoms go away about two days sooner than those in the placebo group. Of 100 people with upper respiratory infections, an estimated 19 additional people would have completely recovered by day seven with zinc treatment. The strength of the evidence was considered low.
  • On day three of the infection, those taking zinc had milder symptoms. Further, there was an 87% lower risk of severe symptoms among those taking zinc. However, the daily average symptom severity was similar between those taking zinc and those taking placebo. The data quality and certainty of these findings were low to moderate.

Spirulina as a supplement: benefits and warnings

Before taking zinc, keep these other points in mind:

Side effects of zinc for colds

Zinc-related side effects were mild. These included nausea and mouth or nose irritation.


Zinc supplements are generally inexpensive. A daily dose of zinc lozenges for a month may cost less than $2/month.

Different doses or types

Additional research is needed to determine the best dose and ideal way to take zinc.

Zinc and COVID-19

None of the studies in this analysis assessed the impact of zinc on the virus causing COVID-19.

Other ways to fight seasonal illnesses

Whether you decide to take zinc or not, keep in mind the following tried and true preventive measures and treatments:

  • Get a flu shot.
  • Wash your hands frequently.
  • Avoid contact, maintain physical distance, and wear a mask around people who are sick.
  • Get plenty of sleep.
  • Choose a healthy diet.

For additional consumer health information, please visit www.health.harvard.edu.

© 2022 Harvard University

For terms of use, please see www.health.harvard.edu. Distributed by Tribune Content Agency, LLC.

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