Schizophrenia is a devastating and complex disease that can include a variety of specific clinical conditions. Drugs to treat schizophrenia have not advanced much beyond the 1960s; in many cases they are not very effective, and they have severe side-effects. The problem is that the cause of schizophrenia is unknown, and precisely how the drugs affect brain circuitry is also unknown. Schizophrenia is thought to have a substantial environmental component (toxins, culture, upbringing, lifestyle, diet, etc.), but its onset is likely to be predisposed by genetic factors. Genetic analysis has recently made great progress in identifying genes that cause diseases. Many diseases that strike young adults, as schizophrenia often does, have been shown to be caused by one or just a few specific mutations. For example, some diseases that cause blindness are now known to be caused by a mutation in one or more of the genes that code for molecules in the brain essential for sight. In one recent case, gene therapy approved by the FDA to correct the mutation has restored sight in blind people. 
Pessimism about schizophrenia
However, research into the possible genetic cause of schizophrenia has not found any obvious candidate gene mutations. Part of the problem is that schizophrenia is not just one disease; it comprises a family of interrelated conditions and is diagnosed by several criteria, which implies that a variety of causes may contribute. Apparently, many gene mutations may contribute to schizophrenia, but none yet found have an influence strong enough to be the exclusive cause.
A recent presentation on solving the puzzle of schizophrenia at the Society for Neuroscience (SfN) conference in Washington DC had a pessimistic tone, explaining that there are no easy answers in the search for better treatment. No helpful novel drug treatments for schizophrenia have been found in recent years, and the lack of obvious genetic markers that are correlated with the disease presents a severe challenge. The SfN presentation, however, didn't mention recent research into dietary causes and treatments for schizophrenia. Niacin cures many schizophrenics
In the early 1960s, Hoffer and Osmond published studies showing that niacin (also known as nicotinic acid or vitamin B3) given at sufficiently high doses could effectively treat some schizophrenia patients.[3-7] Although Hoffer and Osmond's theories about how niacin could treat schizophrenia were never proven sufficiently to convince the rest of the field, their results in treating thousands of patients with niacin therapy and curing many were striking. The term "orthomolecular" was coined by Linus Pauling for the use of essential nutrients such as niacin in preventing disease, and in particular, schizophrenia. Looking for more recent studies, a search on PubMed of the terms "schizophrenia niacin" returns several dozen articles. One of them asserts that some schizophrenics can be well treated with niacin, and refers to Hoffer and Osmond's early studies, reviewing several theories about likely mechanisms. "Abram Hoffer backed up his treatment with clearly explained biochemistry, as he had a degree in biochemistry before obtaining his MD. I personally found his presentation fascinating as well as convincing."
Niacin skin test
Most people get a "niacin flush" on their skin for a few minutes when a large dose of niacin is taken orally. This is a normal consequence of niacin activating prostaglandin pathways that cause vasodilation in the skin and is not harmful. Niacin is utilized by several hundred metabolic pathways in the body, so oral niacin is taken by many to treat illness and maintain good health. To avoid the skin flush, one starts with small doses [typically 25 mg/day] and gradually increases the dose over several days to achieve a therapeutic effect. However, some schizophrenics don't get a niacin flush with the normal doses, suggesting that they have a deficiency of niacin and likely other essential nutrients. Therefore, niacin applied to the skin or taken orally has been used as a test for predisposition to schizophrenia. Hoffer noted that in some cases where schizophrenics recovered, they reverted to a normal skin flush. A flurry of recent studies show that about one third of schizophrenics have a blunted niacin skin flush, suggesting that this test can be used as a diagnostic tool. [12-21] Several of these recent studies attempt to determine from those results what aspect of the metabolic disturbance might cause problems for the brain. Although most of these studies don't explicitly discuss the use of niacin as a treatment, the underlying theme is that niacin treatment can help many schizophrenics.
"Dr. Abram Hoffer observed a recovery to a normal niacin-flush response in an otherwise previously flush-resistant schizophrenic. Dr. Hoffer used either niacinamide or niacin, although he favored the lipodystrophy-correcting/flush-causing niacin form more. He also recommended essential fatty acids."
Many schizophrenic patients have severe nutrient dependencies that can be treated with niacin and other vitamins and nutrients. Several recent studies review the evidence for a benefit from good nutrition (niacin, other B vitamins, vitamin C and D, omega-3 fatty acids, etc.) on brain function. [22-29] The use of niacin therapy for testing and treatment of schizophrenia and many other conditions appears to be rapidly expanding. It is inexpensive and widely used for health, but can also help those in desperate need of treatment. For a therapeutic effect, Hoffer recommended gradually increasing doses up to 3,000 mg/day of niacin in divided doses, along with 2,000 mg/day or more of vitamin C and other essential nutrients. For some people, high doses can cause temporary side effects, so many people take niacin for its health benefit at lower doses (500 - 1,000 mg/day). Niacinamide has similar benefits but does not cause the skin flush. For more on the benefits of niacin, dosing, and possible contra-indications please refer to Hoffer's book "Niacin: the Real Story" .
It is straightforward to understand the historical bias against niacin therapy for schizophrenia. Niacin is inexpensive and can't be patented. And it is known to be effective at preventing heart disease. One can imagine that the drug industry is working to make a form of niacin or a niacin-like drug that can produce profits.