Neuropsychiatric diseases like schizophrenia, depression, Alzheimer’s disease, Parkinson’s disease and more cost billions per year and account for 13% of the global burden of disease (a measure of years of life lost due to premature mortality and living in a state less than full health), according to the World Health Organization.
However, pharmaceutical companies have decided that generating new drugs to treat these disorders are simply too costly to pursue, and are pulling the plug on research and development in this area.
Read more here: http://www.scientificamerican.com/article.cfm?id=a-dearth-of-new-meds
It's Interesting 
Namenda did help my Uncle’s aetlrness, but he became very agitated while using the drug so we stopped using it.