• The efficacy of lithium carbonate as a prophylactic drug against depression in bipolar manic depressive patients was assessed through a double-blind, placebo-controlled study of patients who had histories of recurrent depressions and hypomanias ("bipolar II"). The results revealed that treatment with lithium carbonate resulted in a reduction in the frequency of hypomanic episodes. However, no reduction in the frequency of depressive attacks was observed with lithium carbonate treatment during the study (mean length of study, approximately 16 months), although there was a suggestion that the depressive attacks that occurred during treatment with lithium carbonate might be less severe than with placebo treatment.
Dunner DL, Stallone F, Fieve RR. Lithium Carbonate and Affective DisordersV: A Double-Blind Study of Prophylaxis of Depression in Bipolar Illness. Arch Gen Psychiatry. 1976;33(1):117-120. doi:10.1001/archpsyc.1976.01770010073014