Switch from depression to mania, or from mania to depression.

By means of two retrospective record studies of 300 patients hospitalized for mania, and 906 patients hospitalized for depression, the rate and point of switch from mania to depression and from depression to mania between 1920 and 1981 were investigated. The switch rate is mainly explained by polarity; patients with a previous history of mania/ hypomania have switch rates of 21 per cent (mania to depression) to 29 per cent (depression to mania)-in prospective studies the rates are around 30 per cent. Unipolar depressive patients have a switch rate of 2.7-4.6 per cent, which may be due to potential bipolars. The switches occur about 4 months after onset of the episodes and about 7 weeks after hospital admission (medians). The lack of any significant change within this time period does not support the existence of a substantial drug-induced switch. The majority of switches seem to occur as a consequence of the spontaneous course of bipolar illness.