Does B9 deficiency make people psychotic?

Good question. Vitamin B9 is commonly referred to as Folic Acid or just folate (folic acid). It has been studied extensively. Currently, there is evidence that a folate (folic acid) deficiency during pregnancy can result in the baby having what is called a neuro tube defect. That means, that the central nervous system, can develop abnormally, if there is not enough folate (folic acid) while in utero (in the womb). The jury is out about psychosis.
B9 or folic acid. B9 or Folic Acid deficiency can cause mental depression, confusion, and irritability. I suppose some of these affects could be interpreted as psychosis by the lay public.