The invention concerns dihydroimidazo[5,1-a]-.beta.-carboline compounds of general formula (I) ##STR00001## wherein in particular, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.6 and R.sub.7, identical or different, independently of one another, present a hydrogen, halogen atom, an alkyl, hydroxyl, alkoxy, trihalogenoalkyl, alkylamino, dialkylamino, aryl, arylalkyl, carboxy, alkylcarbonyloxy, acyl, aryloxy or arylalkoxy group; R.sub.5 represents a hydrogen atom, an alkyl or arylalkyl group; and their isomers as well as their addition salts to a pharmaceutically acceptable acid. The inventive compounds are for use in medicine, in particular as hypnotics.