Lithium level and inter-episode symptoms in affective disorder.

Forty-two patients with a history of affective disorder on lithium prophylaxis alone participated in a prospective 1-year study of inter-episode symptoms. Despite expected significant differences in mean plasma lithium level in patients, those with mean levels above the median (0.82 +/- 0.10 mEq/l) did not differ in incidence of major symptoms per visit, in mood shift per visit, or in rate of subclinical symptoms on the General Behavior Inventory from those patients with mean level below the median (0.52 +/- 0.09 mEq/l).