What is it about?

Carrageenan is a sulfated polysaccharide extracted from red seaweed. Since the 1980s, carrageenan has been shown to prevent infections due to several viruses. Recent studies found that it can inhibit the replication of the SARS-CoV-2 virus. We analyzed the findings of 2 RCTs with a total of 254 common cold patients, who were treated with nasal carrageenan. The recovery rate from all colds was increased by 54% in the carrageenan patients. The increase in recovery rate was 139% for coronavirus infections, 119% for influenza A infections, and 70% for rhinovirus infections. The effect of carrageenan on long colds was analyzed as the risk of the cold lasting for over 20 days. Nasal carrageenan reduced the risk of such long colds by 71%.

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Why is it important?

Nasal carrageenan is a safe and cheap treatment, and does not need a prescription. Therefore even moderate effects on the duration and severity of respiratory virus infections may be worth exploring. The common cold is ubiquitous and therefore potential treatments are important.


All 4 RCTs published on nasal iota-carrageenan used 3–4 daily doses. In future research the dose–response relationship should be investigated to identify the optimum dose and frequency of administration. It is also possible that the length of time between the onset of symptoms and the start of treatment has an impact on the effectiveness. The 2 RCTs included in our meta-analysis started treatment within 36–48h of symptom onset. In comparison, the corresponding time limit in several zinc lozenge trials was usually 24 h. The effect of the time between the onset of symptoms and the start of carrageenan treatment should therefore be investigated in further trials. Given the particular concern around long cases of COVID-19, and the demonstrated effect of carrageenan on the old coronaviruses, the proportionally greater effect of carrageenan on long common cold infections seems particularly important and encourages further study.

Dr Harri Hemila
Helsingin Yliopisto

Read the Original

This page is a summary of: Carrageenan nasal spray may double the rate of recovery from coronavirus and influenza virus infections: Re‐analysis of randomized trial data, Pharmacology Research & Perspectives, June 2021, Wiley,
DOI: 10.1002/prp2.810.
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