This prospective study examined the incidence of mania or hypomania in
230 patients with recurrent depression treated with imipramine. Overall,
only six individuals (2.6%) developed hypomania, representing 0.9% of those
in the acute phase and 2.5% of those in the continuation phase of drug
treatment. Patients with a history of bipolar II depression (N = 33) did
not have a greater incidence of hypomania than those with unipolar
depression (N = 197). Younger patients did not switch to hypomania more
rapidly than older ones, and women were not more likely to switch than men.
Systematic assessment of mania, stringent diagnostic criteria, and the
recurrent nature of the sample may account for this low incidence of
hypomania compared to that reported by other investigators.