When you are looking for studies, make sure they are double-blind, placebo controlled studies. Preferably from a reputable source, like nimh.gov. Some journals will publish shady studies just to make a quick buck.
I don't have time to link them right now, but studies have shown Sarcosine helps to treat negative symptoms, and works best along with antipsychotics. Fish oil has been shown to help prevent somebody in the prodromal stage of schizophrenia from progressing into full-blown symptoms. If you use the search bar on this site, you will find links to those studies.