Despite important progress, the results of pharmacological treatment of schizophrenia are frequently unsatisfactory. Therefore some patients use natural medicines although it is unclear whether natural medicines are effective and safe. We assessed the evidence for natural medicines with and without antipsychotics in treating symptoms or reducing side effects of antipsychotics in schizophrenia.

A systematic review until April 2013. Only RCTs with a Jadad score of 3 or higher, were included.

105 RCTs were identified. Evidence was found for glycine, sarcosine, NAC, some Chinese and ayurvedic herbs, ginkgo biloba, estradiol and vitamin B6 for improving symptoms of schizophrenia when added to antipsychotics. Inconclusive or no evidence was found for omega-3, Dserine, D-alanine, D-cycloserine, B vitamins, vitamin C, dehydroepiandrosteron (DHEA), pregnenolone (PREG), inositol, gamma-hydroxybutyrate (GHB) and des-tyr-gamma-endorphin when added to antipsychotics. Omega-3 without antipsychotics might be beneficial in the prevention of schizophrenia. Only ayurvedic herbs (in one study), no other agents, seemed effective without antipsychotics. Ginkgo and vitamin B6 seemed to be effective in reducing side effects of antipsychotics. All natural agents produced only mild or no side-effects.

High quality research on natural medicines for schizophrenia is scarce. However, there is emerging evidence for improved outcome for glycine, sarcosine, NAC, some Chinese and ayurvedic herbs, ginkgo biloba, estradiol and vitamin B6, all with only mild or no side effects. Most study samples are small, the study periods are generally short, the studies only cover a modest part of the world's population and most results need replication.