Provided herein are compounds of the formula (I): ##STR00001## wherein R.sup.1-R.sup.8 are as described herein, R.sup.4 being phthalazinyl, pyrazinyl, pyridazinyl, or quinoxalinyl. Such compounds are particularly useful in the treatment of a disorder which is created by or is dependent upon decreased availability of serotonin, norepinephrine, or dopamine.