Here is a though: if anti-psychotic drugs are effective against type two diabetes, then perhaps a diet that reduces carb intake and insulin production would help with psychotic issues.
Not that very many will be interested in researching that as there is no money to be made by recommending dietary changes but lots to be made off of medications.
The old double-think. Sometimes playing devils advocate and transposing known treatments does result in new breakthroughs. I have also read that ECT (electro shock therapy) for depression is making a modest comeback as a treatment option for severe depression that proves resistant to drug therapy. Following.
As a diabetic and a sufferer of Bi-polar, I can tell you that letting your blood sugar get out of control will f**k your head up.