It's produced from tryptophan, same as serotonin, also melatonin. Niacin deficiency causes pellegra, some of the symptoms are schizophrenic-like. Leading to the theory of niacin as a schizophrenia therapy--which I'm very skeptical of, all you have to do is come across a particular cohort of "schizophrenics" who are actually niacin deficient, and you have evidence of niacin as a therapy. Then again, there have been cases of mania and depression that turned out to be symptoms of thyroid disorders, so it's probably worth looking out for, all the same.