Dibenzosuberanyl piperazine derivatives represented by the following formula (I): ##STR1## wherein R represents an aliphatic hydrocarbon group, which may contain one or more heteroatom-containing substituent groups and may preferably contain 2 to 30 carbon atoms, and physiologically acceptable salts thereof; and medicinal compositions containing these dibenzosuberanyl piperazine derivatives and/or physiologically acceptable salts thereof. These compounds show effectiveness in allowing resistance-acquired causes of diseases to restore sensitivity to drug, that is, a resistance overcoming effect.
