Several traditional Japanese
Kampo formulas are known to have inhibitory effects on
infections with viruses that cause respiratory symptoms. Although some herbs and their components have been reported to suppress SARS-CoV-2 replication in vitro, it is difficult to compare effective
Kampo formulas because of the different methods used in studies. Thus, we carried out in vitro experiments on the suppression of
SARS-CoV-2 infection by
Kampo formulas and crude drugs used for the
common cold to compare their suppressive effects on
virus infection. After infecting VeroE6/TMPRSS2 cells with SARS-CoV-2, lysates of the
Kampo formulas and crude drugs were added, and after 24 h, the infectious titer in the medium was measured by the TCID50 method.
Maoto was the most effective among the
Kampo formulas, and
Ephedrae herba was the most effective among the constituent crude drugs. However, a comparison of the suppressive effects of
Ephedrae herba and
Kampo formulas containing
Ephedrae herba showed that the suppressive effect on
virus infection did not depend on the content of
Ephedrae herba. Based on the results, we believe that the use of
Maoto among
Kampo formulas is suitable as a countermeasure against
COVID-19.