Estimating the per-protocol effect of lithium on suicidality in a randomized trial of individuals with depression or bipolar disorder.

With one-third of the targeted sample size, lithium effects (compared with placebo) ranging between a 17.5% reduction and a 5.5% increase in the risk of suicidality were highly compatible with the data. Thus, a protective effect of lithium on suicidality among patients with bipolar disorder or major depressive disorder cannot be ruled out. Trials should incorporate adequate per-protocol analyses into the decision-making processes for stopping trials for futility.