Orthomolecular medicine debunked:
The human body has limited capacity to use vitamins in its metabolic activities. When vitamins are consumed in excess of the body's physiological needs, they function as drugs rather than vitamins. A few situations exist in which high doses of vitamins are known to be beneficial, but they must still be used with caution because of potential toxicity. For example, large doses of niacin can be very useful as part of a comprehensive, medically supervised program for controlling abnormal blood cholesterol levels. "Orthomolecular" practitioners go far beyond this, however, by prescribing large amounts of supplements to all or most of the patients who consult them. This approach can result in great harm to psychiatric patients when used instead of effective medications.
http://www.quackwatch.org/01QuackeryRelatedTopics/ortho.html
Here's an interesting article on Dr. Abram Hoffer, the originator of the pyroluria hypothesis and advocate for vitamin treatment of schizophrenia.
http://www.sciencebasedmedicine.org/index.php/pyroluria-and-orthomolecul...