Marrubiin, a furane labdane diterpene, is the main analgesic compound present in Marrubium vulgare, a medicinal plant used in Brazil and other countries to treat several ailments. Considering its important pharmacological action, as well as its high yield, some structural modifications were performed in order to obtain more active compounds. Success was obtained in reducing the lactonic function, in the formation of marrubiinic acid and two esterified derivatives, which exhibited significant analgesic effect against the writhing test in mice. Marrubiinic acid showed better activity and excellent yield, and its analgesic effect was confirmed in other experimental models of pain in mice, suggesting its possible use as a model to obtain new and potent analgesic agents.