(+)-Menthol (D-Menthol) is one of the optical isomers of Menthol. (+)-Menthol can reduce the electrically evoked contractions of rat phrenic hemidiaphragm in vitro. Local anaesthetic activity. (+)-Menthol can also inhibit the growth of Microcystis aeruginosa cells[2].In Vitro: (+)-Menthol (0.0001-0.1 μg/ml) reduces the electrically evoked contractions of rat phrenic hemidiaphragm dose-dependently in vitro, up to complete abolishment of contractions. .