Updated: Sep 28, 2019
A colleague told me that lithium only prevents suicide in bipolar illness, while clozapine prevents suicide in schizophrenia. Is that true?
Lithium was shown to prevent completed suicide in four randomized clinical trials versus placebo in both bipolar illness and unipolar depression, so its benefit is not limited to bipolar illness, but applies to all mood illnesses. Further, the epidemiological water studies, though not randomized, provide reasonable evidence that lithium likely prevents completed suicide in all human beings, irrespective of diagnosis.
In contrast, clozapine was studied in one randomized clinical trial versus olanzapine, and it did not prevent completed suicide at all, because there were no completed suicides in that trial. Clozapine did reduce suicide attempts versus olanzapine in that study of schizophrenia.
Thus, overall, there are randomized data for prevention of completed suicide with lithium, but not clozapine, and lithium's benefit extends to all mood illnesses, not just bipolar illness, and in fact appears to be generalizable to the entire population. Clozapine's benefit is limited to schizophrenia based on the available data, and reflects on suicide attempts, but has not been shown to reduce actual suicide.