Effects of green tea gargling on Coronavirus Disease-2019: A multi-center randomized controlled trial

Kawai et al., AJPM Focus, doi:10.1016/j.focus.2026.100517, May 2026
Hospitalization 67% improvement lower risk ← → higher risk Pneumonia 67% Case, FAS 1% Case, PPS, Cox 18% Case, PPS, multivaria.. 18% Green tea gargling  Kawai et al.  PROPHYLAXIS RCT Is prophylaxis with green tea gargling beneficial for COVID-19? RCT 1,003 patients in Japan (April 2024 - August 2025) Lower hospitalization (p=0.5) and progression (p=0.5), not sig. c19early.org Kawai et al., AJPM Focus, May 2026 0 0.5 1 1.5 2+ RR
RCT 1,012 adults in Japan showing no statistically significant reduction in COVID-19 incidence with green tea gargling compared to water gargling. In the full analysis set, incidence was 5.4% in both groups. In the per-protocol set (PPS, gargling adherence ≥80%), green tea gargling showed a 23% relative risk reduction, without statistical significance. One hospitalization due to COVID-19 pneumonia occurred in the water gargling group.
No adverse events related to gargling were observed. The study was open-label, which may have introduced performance bias. The study was likely underpowered, as the observed control incidence (5.4%) was lower than the assumed 7.8% used for sample size calculations. Additionally, ~64-67% of participants in both groups reported habitual green tea consumption, which may have attenuated any detectable difference between groups.
Authors hypothesize that higher gargling frequency and catechin concentrations may be needed to achieve sufficient pharyngeal exposure to block ACE2 receptor binding by SARS-CoV-2.
Standard of Care (SOC) for COVID-19 in the study country, Japan, is very poor with very low average efficacy for approved treatments1. Only expensive, high-profit treatments were approved for early treatment. Low-cost treatments were excluded, reducing the probability of early treatment due to access and cost barriers, and eliminating complementary and synergistic benefits seen with many low-cost treatments.
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risk of hospitalization, 66.7% lower, RR 0.33, p = 0.50, treatment 0 of 503 (0.0%), control 1 of 500 (0.2%), NNT 500, relative risk is not 0 because of continuity correction due to zero events (with reciprocal of the contrasting arm).
pneumonia, 66.7% lower, RR 0.33, p = 0.50, treatment 0 of 503 (0.0%), control 1 of 500 (0.2%), NNT 500, relative risk is not 0 because of continuity correction due to zero events (with reciprocal of the contrasting arm).
risk of case, 0.6% lower, RR 0.99, p = 1.00, treatment 27 of 503 (5.4%), control 27 of 500 (5.4%), NNT 3105, FAS population.
risk of case, 17.6% lower, HR 0.82, p = 0.56, treatment 386, control 403, PPS population, Cox proportional hazards.
risk of case, 18.2% lower, OR 0.82, p = 0.56, treatment 386, control 403, adjusted per study, PPS population, multivariable, RR approximated with OR.
Effect extraction follows pre-specified rules prioritizing more serious outcomes. Submit updates
Kawai et al., 31 May 2026, Randomized Controlled Trial, Japan, peer-reviewed, 19 authors, study period 1 April, 2024 - 28 August, 2025. Contact: ykawai@u-shizuoka-ken.ac.jp.
$0 $500 $1,000+ Efficacy vs. cost for COVID-19 treatment protocols c19early.org June 2026 Japan USA Angola Colombia Kenya Mozambique Myanmar South Africa Peru Philippines Vietnam China Uzbekistan Iran Bangladesh Ethiopia Ghana Germany Mexico South Korea Saudi Arabia Algeria Morocco Yemen Poland India Venezuela DR Congo Madagascar Thailand Uganda Egypt Nigeria Taiwan Zambia Bolivia Fiji Bosnia-Herzegovina Ukraine Côte d'Ivoire Bulgaria Greece Slovakia Singapore Iceland New Zealand Trinidad and Tobago Mongolia Czechia Israel Belarus North Macedonia Hong Kong Qatar Panama Serbia CAR Syria Japan favored high-profit treatments.The average efficacy of treatments was very low.High-cost protocols reduce early treatment, andforgo complementary/synergistic benefits. More effective More expensive 75% 50% 25% ≤0%
$0 $500 $1,000+ Efficacy vs. cost for COVID-19treatment protocols worldwide c19early.org June 2026 Japan USA Angola Colombia Kenya Mozambique Myanmar South Africa Peru Philippines Vietnam China Uzbekistan Iran Bangladesh Ethiopia Ghana Germany Mexico South Korea Saudi Arabia Algeria Morocco Yemen Poland India Venezuela DR Congo Madagascar Thailand Uganda Egypt Nigeria Taiwan Zambia Bolivia Fiji Ukraine Côte d'Ivoire Eritrea Bulgaria Greece Slovakia Singapore Iceland New Zealand Mongolia Czechia Israel Belarus North Macedonia Hong Kong Qatar Panama Serbia CAR Japan favored high-profit treatments.The average efficacy was very low.High-cost protocols reduce early treatment,and forgo complementary/synergistic benefits. More effective More expensive 75% 50% 25% ≤0%
EGCG (epigallocatechin gallate) is a small molecule polyphenol derived from Camellia sinensis that exhibits antiviral activity against SARS-CoV-2 via dual mechanisms: blocking viral entry by interfering with the Spike-ACE2 receptor interaction and inhibiting the viral 3CL protease (Mpro). Additionally, EGCG provides anti-inflammatory effects by modulating cytokine production, potentially mitigating the cytokine storm associated with severe COVID-19.
Abstract: ELSEVIER AJPM FOCUS Journal Pre-proof Effects of green tea gargling on Coronavirus Disease-2019: A multi-center randomized controlled trial BGOM Yasue Kawai , Yoshihiko Ito , Takahiro J. Nakamura , Daisuke Furushima , Yuina Nakai , Motoyasu Miura , Shinya Uchida , Keiko Unno , Yoriyuki Nakamura , Norikata Takuma , Takatsugu Ikukawa , Mitsuo Kimata , Chika Tagata , Makoto Kobayashi , Masaki Ichitani , Takanobu Takihara , Hitoshi Kinugasa , Ichiro Kato , Hiroshi Yamada PII: S2773-0654(26)00043-X DOI: https://doi.org/10.1016/j.focus.2026.100517 Reference: FOCUS 100517 To appear in: AJPM Focus Received date: 22 December 2025 Revised date: 18 May 2026 Accepted date: 18 May 2026 Please cite this article as: Yasue Kawai , Yoshihiko Ito , Takahiro J. Nakamura , Daisuke Furushima , Yuina Nakai , Motoyasu Miura , Shinya Uchida , Keiko Unno , Yoriyuki Nakamura , Norikata Takuma , Takatsugu Ikukawa , Mitsuo Kimata , Chika Tagata , Makoto Kobayashi , Masaki Ichitani , Takanobu Takihara , Hitoshi Kinugasa , Ichiro Kato , Hiroshi Yamada , Effects of green tea gargling on Coronavirus Disease-2019: A multi-center randomized controlled trial, AJPM Focus (2026), doi: https://doi.org/10.1016/j.focus.2026.100517 This is a PDF of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability. This version will undergo additional copyediting, typesetting and review before it is published in its final form. As such, this version is no longer the Accepted Manuscript, but it is not yet the definitive Version of Record; we are providing this early version to give early visibility of the article. Please note that Elsevier's sharing policy for the Published Journal Article applies to this version, see: https://www.elsevier.com/about/ policies-and-standards/sharing#4-published-journal-article. Please also note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. - © 2026 Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Highlights - This study evaluated green tea gargling vs water in Japan - 22.8% lower COVID-19 incidence was observed with green tea use - Gargling with green tea may help prevent COVID-19 - Results lack statistical significance; more research needed to confirm effects Effects of green tea gargling on Coronavirus Disease-2019: A multi-center randomized controlled trial Authors: Yasue Kawai a , Yoshihiko Ito b , Takahiro J. Nakamura c , Daisuke Furushima d Yuina Nakai e , Motoyasu Miura e , Shinya Uchida e , Keiko Unno f , Yoriyuki Nakamura f Norikata Takuma g Takatsugu Ikukawa h , Mitsuo Kimata i , Chika Tagata j Makoto Kobayashi j , Masaki Ichitani j , Takanobu Takihara j , Hitoshi Kinugasa j Ichiro Kato j , Hiroshi Yamada a Affiliations: | a Department of Tea & Health Sciences Graduate School of Pharmaceutical Sciences, | |---------------------------------------------------------------------------------------------------| | University of Shizuoka, 52-1, Yada Suruga-ku, Shizuoka 422-8526, Japan | | b Department of Drug Evaluation & Informatics School of Pharmaceutical Sciences, | | University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan | | c Laboratory of..
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