There has been quite a bit of good research over the past 8 years on a dietary supplement called Sarcosine (or N-methyl Glycine). It is a natural amino acid that you have already in your body.
Sarcosine seems to be the only thing that has some good clinical research data showing that it can help people who have schizophrenia and who suffer from some negative symptoms (the cognitive/focus issues, lack of motivation, and negative mood/depression issues that are common with schizophrenia.
We have a new summary of this research here that we encourage you to read:
It is available from a number of online stores at different prices. BrainVitaminz and Profrontal are companies focused on brain vitamins and are run by scientists, medical people and PHDs. Smartpowders is primarily a supplement company for body builders. We would trust the companies that are focused on brain supplements more than a company focused on bodybuilders.
$13.99 from http://brainvitaminz.com/
$25.99 for 180 Grams (Best value) - http://brainvitaminz.com/products/sarcosine-180-gram
$49.99 from http://profrontal.com/
Here is a summary view of the results from a double blind, placebo-controlled study: