Domperidone monomaleate (R33812 monomaleate) is a potent antagonist of dopamine D2 receptor that acts as an antiemetic and prokinetic agent by targeting the chemoreceptor trigger zone and motor function of the stomach and small intestine. It also inhibits cardiac Na⁺ channels such as Nav1.5, suggesting a potential molecular mechanism for cardiovascular side effects like malignant arrhythmias.