This invention is directed to a method for preventing or treating bipolar disorder comprising administering to a subject in need thereof a therapeutically effective amount of an enantiomer of Formula (I) or enantiomeric mixture wherein one enantiomer of Formula (I) predominates: ##STR00001## wherein phenyl is substituted at X with one to five halogen atoms selected from the group consisting of fluorine, chlorine, bromine and iodine; and, R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen and C.sub.1 C.sub.4 alkyl; wherein C.sub.1 C.sub.4 alkyl is optionally substituted with phenyl (wherein phenyl is optionally substituted with substituents independently selected from the group consisting of halogen, C.sub.1 C.sub.4 alkyl, C.sub.1 C.sub.4 alkoxy, amino, nitro and cyano).