Compounds of formula (I): wherein A is S or O; R is H; Ar is an optionally substituted phenyl group; X is an optionally substituted phenyl group, a C1-C4 alkyl, a C3-C6 cycloalkyl group or a CH2(C3-C6 cycloalkyl) group; R′ is H or C1-C4 alkyl; and each R1 is independently H or C1-C4 alkyl; and pharmaceutically acceptable salts thereof are selective inhibitors of norepinephrine reuptake.