The invention relates to 1,3,4,16b-tetrahydro-2H,10H-indolo[2,1-c]pyrazino[1,2-a][1,4]benzodiaz epine derivatives of the formula I, IMAGE (I) wherein R1 is hydrogen, lower alkyl, C3-7-alkenyl, C3-7-alkynyl, 3 to 7 ring-membered cycloalkyl, C2-7-alkyl substituted by a substituent selected from hydroxy, amino, N-mono-lower alkyl-amino and N,N-di-lower alkyl-amino; or R1 is lower alkyl substituted by a substituent selected from 3 to 7 ring-membered cycloalkyl, carboxy, lower alkoxycarbonyl, carbamoyl, N-mono-lower alkyl-carbamoyl, N,N-di-lower alkyl-carbamoyl and lower alkanoyl; or R1 is lower alkyl substituted by either phenyl or benzoyl each of said phenyl or benzoyl radicals being unsubstituted or substituted by up to three members selected from lower alkyl, lower alkoxy, lower alkylthio, halogen and trifluoromethyl; R2 and R3 represent hydrogen, lower alkyl, hydroxy, lowr alkoxy, halogen or trifluoromethyl; and R4 represents hydrogen, lower alkyl, hydroxy-lower alkyl, carboxy, lower alkoxycarbonyl, carbamoyl, N-mono- or N,N-di-lower alkyl-carbamoyl, or formyl; salts and 2N-oxides; which are useful as serotonin-2 receptor antagonists.
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