Crude extracts of the aerial parts of Marrubium vulgare show a potent in vitro inhibition of KCl-induced contraction of rat aorta. Bio-guided fractionations, spectroscopic analysis and chemical derivatization revealed the furanic labdane diterpenes marrubenol and marrubiin as the most active compounds.
El Bardai, S., Morel, N., Wibo, M., Fabre, N., Llabres, G., Lyoussi, B., & Quetin-Leclercq, J. (2003). The vasorelaxant activity of marrubenol and marrubiin from Marrubium vulgare. Planta Medica : natural products and medicinal plant research, 69(1), 75-77. https://doi.org/10.1055/s-2003-37042 (Original work published 2003)