Determination of the optimal concentration of lithium for the prophylaxis of manic-depressive disorder.

A group of 29 bipolar manic-depressives completed a 12-month double-blind cross-over trial of low-dose and high-dose lithium prophylaxis. Twelve patients relapsed, and significantly more of the relapses occurred during the low-dose 6-month phase of the trial. There was a trend for relapse to occur within 2 months of an abrupt drop in plasma lithium level, and to occur more often in women than in men. The efficacy of low-dose lithium prophylaxis and the significance of rebound relapse are discussed.