Depression
Eat Vitamin B complex, folic acid, S-adenosylmethionine, and Selenium. Fresh air and sunlight help too.
Schizophrenia
Eat folic acid, Vitamin-C, and Vitamin-E. There are some reports that Zinc, Manganese, and Niacin can help.
ADHD
Try a high protein, low carb, sugar free diet, with supplements of Omega-3, Vitamin B3, B6, and B1. Small amounts of caffeine (150-300 mg) may help. Avoid Red-40