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Effects of Green Tea Gargling on COVID-19: A Multicenter RCT
Yasue Kawai1, Yoshihiko Ito2, Takahiro Nakamura3
1Department of Tea & Health Sciences, Graduate School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
AJPM Focus
|August 4, 2026
Summary
Green tea gargling showed a potential 22.8% relative reduction in COVID-19 incidence, though not statistically significant. Further research is needed to confirm the preventive effects of green tea for COVID-19 prevention.
Area of Science:
- Medical Research
- Public Health
- Infectious Diseases
Background:
- Catechins from green tea are investigated for COVID-19 prevention.
- Clinical evidence for green tea's preventive effects against COVID-19 is lacking.
- This study evaluates green tea gargling as a preventive measure for COVID-19.
Purpose of the Study:
- To assess the preventive efficacy of green tea gargling against COVID-19.
- To compare COVID-19 incidence between green tea and water gargling groups.
- To identify potential benefits of green tea components like catechins.
Main Methods:
- A multicenter randomized controlled trial (RCT) involving 1,012 adults.
- Participants gargled three times daily for 12 weeks with either green tea or water.
- Data analyzed using multivariate logistic regression and Cox proportional hazards models.
Main Results:
- COVID-19 incidence was 5.4% in both green tea and water gargling groups (full analysis).
- In the per-protocol set (adherence ≥80%), green tea showed a 22.8% relative reduction in incidence (4.4% vs. 5.7%).
- No statistically significant difference was found; no gargling-related adverse events occurred.
Conclusions:
- Green tea gargling did not demonstrate a statistically significant preventive effect against COVID-19.
- A trend towards reduced incidence was observed, warranting further investigation.
- Optimizing gargling frequency and catechin concentration may be key for future studies.
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